| Station | Phraseology |
| **Pilot** | München Apron good day, DLH5KC, stand 205A, request pushback. |
| **ATC** | DLH5KC, München Apron good day, pushback approved, facing south. |
| **Pilot** | Pushback approved, facing south, DLH5KC. |
| Station | Phraseologie |
| **Pilot** | DLH5KC, request taxi. |
| **ATC** | DLH5KC, taxi to entry S8 via W2 D2 O2. |
| **Pilot** | Taxi to entry S8 via W2 D2 O2, DLH5KC. |
| **ATC** | TUI4PH taxi to holding point runway 18 via L N1 N, hold short of N5. |
| **ATC** | TUI4PH continue taxi via N. |
| **ATC** | RYR1ME taxi to holding point runway 24 via B A A3, hold short of runway 14L. |
| **ATC** | DLH5KC give way to company A320 crossing right to left on D3. |
| **Pilot** | München Ground hallo, DLH5KC Entry S8, able B12. |
| **ATC** | DLH5KC, hallo, taxi to holding point runway 26L, intersecton B12, via B12. |
| **ATC** | DLH5KC, hallo (no benefit), taxi to holding point runway 26L via S and B13. |
| **ATC** | DLH5KC, advise able to depart from runway 26L, intersection B10. |
| **ATC** | DLH5KC revision, continue via W2, hold short of D4. |
| **ATC** | DLH123, pushback approved, then pull foreward, disconnect (tug) short of D2 / abeam stand 217. |
| **ATC** | DLH123, when clear of outbound company A320 behind, pushback approved. |
| **ATC** | DLH123, when space permits, pushback approved. |
| **ATC** | DLH123, when clear of the inbound British Airways A319 for V117, pushback approved, orange line, facing west. |
| **ATC** | DLH123 give way to the vacating Condor A320 from runway 25C. |
| **Pilot** | Giving way to the vacating traffic, DLH123. |
| **ATC** | CFG789 number one, taxi right via L, hold short of N8. |
| **ATC** | DLH123, taxi right on L, hold short N8. |
| Backtrack | |
| DLH5EJ, backtrack approved, line up runway 03 | DEEZU, Zurückrollen genehmigt, rollen Sie zum Abflugpunkt Piste 03 |
In short, remember: "Flying before taxiing before standing".
Priorities are particularly important for time-critical instructions where a few seconds can be crucial (e.g. landing clearance on short final). These priorities also help to ensure your own efficiency, a good use of the airport’s capacity and to avoid frequencies that are too full. ##### Giving and labeling standbys When there is a lot of traffic, for the reasons mentioned above, it is no shame at all if the less important things such as enroute clearances are put on standby for a few minutes. In cases like this, you can say something like "DLH123, standby, number 2 for clearance" to the pilot. A standby can also be useful for other reasons, e.g. because the pushback cannot yet be given due to other traffic: "DLH123, standby for pushback due to traffic". To keep an overview of which aircraft have been given a standby, you can use the request column in the startup or departure list, at least for the outbounds, to highlight standbys so that you don't have to remember them. If, for example, a plane calls in for pushback or enroute clearance and this cannot yet be given for whatever reason, you go to the corresponding line, click on the REQ column and then go to the fitting clearance. You will then see "R1P" in yellow, for example. The "R" stands for request, the number for the number of the aircraft's turn (e.g. 2 if another aircraft before it has the same standby) and the "P" for the type of request (C = clearance, P = pushback, T = taxi, etc.). Optionally, you can also show the timer column by right-clicking on the "O" in the top left of the list and then activating "Timer". You can then see how long a plane has been waiting. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2024-03/screenshot-8.png) Finally, you should get into the habit of checking the REQ column regularly so you never forget standbys again. # Tower EfficiencyThis procedure is not a mandatory part of S1 training.
#### IntroductionUnder certain circumstances, a take-off or landing clearance can be issued even if the runway is not clear yet. However, there must be **reasonable assurance** that the **runway will be clear** as soon as the **inbound aircraft crosses the runway threshold** or the **outbound aircraft begins its take-off run**.
This procedure can reduce the frequency load and increase efficiency on the frequency, especially when traffic volumes are high. However, applying it appropriately requires a high level of knowledge and experience. The crux of the matter is the requirement of "*reasonable assurance*" for a clear runway as soon as the take-off or landing clearance takes effect. Of course the term "reasonable assurance" allows for a wide variety for interpretation. Because flight safety is nevertheless the top priority in all procedures, it is advisable to delete the word "reasonable" from your own mindset if possible and only apply the procedure if there is "assurance" that the relevant conditions will be met at the necessary time. #### Takeoff clearance **Situation (A)**: Without the procedure described in this article, I may not issue a take-off clearance at this time, as GREEN has not yet crossed the runway end and the runway is therefore still occupied. But considering "reasonable assurance", a controller can issue the take-off clearance at the time of situation A if they have "reasonable assurance" that GREEN will have already flown over the end of the runway and the runway will be clear when BLUE begins the take-off run. This situation is illustrated in **situation (B)**. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2022-11/atd-nichtzuruckhalten-start-v2.png) This procedure can also be used under reduced runway separation (RRS). Wake turbulence and/or radar separation must still be ensured if necessary. #### Landing clearance **Situation (A):** Without the procedure described in this article, a landing clearance would not be possible as the runway is still blocked by the landing aircraft GREEN. As controller, however, I can clear the landing by "not holding back a landing clearance" if I have "reasonable assurance" that GREEN will already have left the runway and the runway will therefore be clear when BLUE crosses the runway threshold. In **situation (B)**, the above has occurred and the procedure has been applied correctly. However, for the reasons mentioned under "Take-off clearance", it is difficult to predict the speed when an aircraft leaves the runway and thus to achieve "reasonable assurance". [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2022-11/atd-nichtzuruckhalten-landung-v2.png) The procedure can also be used if a departure takes place before the landing traffic. Once this has taken off, it is relatively easy to predict with "reasonable assurance" whether the runway will be clear when the approach crosses the runway threshold. In this case, the landing clearance may be given before the departure has flown over the runway end, provided that the runway will be clear when the approach flies over the runway threshold. This procedure can also be used under [reduced runway separation](https://knowledgebase.vatsim-germany.org/books/separation/page/reduced-runway-separation-rrs "Reduced runway separation (RRS)") (RRS). Wake turbulence and/or radar separation must still be ensured if necessary. #### Phraseology The phraseology does not change compared to the "normal" take-off and landing clearances. Traffic information is **not** mandatory when using this procedure. However, as always, traffic information can contribute to better situational awareness on the part of pilots and controllers. #### Examples The main purpose of this procedure is to use the frequency more efficiently, especially when there is a lot of traffic, by for example avoiding a second unnecessary radio call. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2024-03/screenshot-9.png) Example 1 (see picture): DLH9AX is at the holding point and reports ready. The previous departure is airborne and will have flown over the end of the runway in approx. 10 seconds. Thanks to this procedure, I can give the takeoff clearance directly, even though there is no runway separation at this point. I have reasonable assurance that the runway separation will exist at the time when the following aircraft begins its takeoff run, as certainly there will be more than 10 seconds between the lineup instruction and the start of the takeoff run. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2024-03/screenshot-10.png) Example 2 (see picture): TAM8070 reports on 8 NM final approach. The previous inbound has landed and is slowing down on the runway. Thanks to this procedure, I can give the inbound caller their landing clearance directly with the initial call, even though there is no runway separation at that time. I have reasonable assurance that the runway separation will exist at the time when the following inbound flies over the runway threshold, as it still needs approx. 3 minutes to reach the runway and the leading inbound is about to leave the runway. Of course, as the controller I still have to monitor the situation and if for any reason the separation is not given, I have to withdraw the clearance. The procedure should **not be used in close situations** (e.g. if the following inbound is already on short final and the leading inbound has not yet completely left the runway). In this case there is **no** reasonable assurance about the separation at the time of the threshold overflight. Instead, you should delay the landing clearance until the runway has actually been cleared. # Conditional Lineup ##### Introduction At all controller stations, it is extremely important to use the frequency as efficiently as possible. In our heads, we may be able to think about and work on two things at the same time, but on frequency, we cannot give two instructions to different aircraft at the same time. This makes it advisable to prioritize transmissions in order to have time for other transmissions later. An ideal option for this is the conditional lineup clearance. It allows you to delegate the clearance to the pilot and instruct him to taxi onto the runway after a certain amount of traffic. It is important to always tell the pilot exactly which traffic is involved! There must also be good visibility so that the pilot can see the other aircraft. If the weather conditions are poor or the angle of the intersection is unfavorable (more acute than 90°), the pilot must first be asked whether he can see the traffic in question. As mentioned above, this procedure is intended to make better use of gaps in the frequency and thus increase efficiency. It should be noted that a conditional clearance is significantly longer and takes more time than a standard one. Depending on the traffic situation, a conditional clearance can be significantly more efficient than a normal lineup. If, for example, one can expect that by the end of the call the landing traffic has already flown over the runway threshold or someone else has already started the take-off run, a normal lineup is probably more suitable ##### For departures When traffic volumes are high, it can be very important on some airports to achieve efficient spacing of departures and not lose any time. To make this possible, the outbounds should start their lineups as soon as possible. Here, the controller can work well in advance and guide the aircraft onto the runway according to their planned departure sequence. Several conditional clearances at the same time are only possible if the restricting aircraft is the closest aircraft to the restricted aircraft. This is explained further in the example below. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2022-10/atd-condinional-lineup.png) *Example for a conditional lineup in Frankfurt runway 25C (click for full screen)*| Station | Phraseologie |
| **ATC** | DLH720, **behind** departing Boeing 777, lineup runway 25C **behind**, number 3 for departure. |
| **Pilot** | **Behind** departing Boeing 777, lining up runway 25C **behind**, number 3, DLH720. |
| **ATC** | SAS638, **behind** next departing Boeing 777 full length, lineup runway 25C **behind**. |
| **Pilot** | **Behind** departing Boeing 777 full length, lineup runway 25C **behind**, SAS638. |
| **ATC** | DLH8JR, behind departing company Airbus A380 via L3, lineup runway 25C and wait behind, number 4. |
| Station | Phraseologie |
| **ATC** | DLH5KC, **behind** next landing A320 on 2 NM final, lineup runway 26L **behind**. |
| **Pilot** | **Behind** next A320, lining up runway 26L behind. |
An **additional requirement** for departure spacing most airports require a minimum spacing between consecutive departures on the **same SID** of least **5 NM** (see your training airport's **SOP** for details).
While separation always describes the absolute minimum, spacing is a value that is always at least equal to or greater than the separation minimum and includes an optional safety margin. In mathematical terms: Spacing = separation minimum + optional safety margin. The approach or center controller may also specify a departure spacing in individual cases if the airspace is very full. An **MDI**, i.e. **Minimum Departure Interval**, usually expressed in minutes, can also be imposed here. With the restriction "MDI CINDY 5 minutes", for example, the tower controller may allow departures to waypoint CINDY only with an interval of at least 5 minutes. To summarize, here is a short workflow that quickly and easily provides you with the correct minimum distance between two departures. Ideally and in the spirit of proactive controlling, you should not wait until the two aircraft concerned are already at the holding point to go through this flow. Do it as early as possible. Example: I give two pilots a clearance for pushback at the same time and already simultaneously consider what departure spacing will later be required on the runway. Everything that has already been planned only needs to be put into action and you have capacity for other things. If your aircraft are on different SIDs, move to the left half of the table and go through the three bullet points: Radar Separation is always 3NM (on both sides). The largest value of the three bullet points is your minimum departure spacing.**Example:** A340 ahead, C172 behind, different SID - Radar Separation Minimum? 3 NM
- WTC Minimum? 6 NM
- Spacing? 3 NM
=> WTC biggest, so minium **6 NM**
| **Beispiel:** A320 ahead, A320 behind, same SID - Radar Separation? 3 NM - WTC Minimum? 0 NM - Spacing? 5 NM => Spacing biggest, so minium **5 NM** |
**In general**, if you are not sure about something, always ask. Especially the colleagues on APP and CTR usually have more experience and will be happy to help you
### Inbounds The handling of approaches for you as a tower controller can be explained quickly. You receive approaching aircraft from the approach controller approximately 8 - 12 NM before the runway. If you have approaching traffic on your frequency, you should give them clearance to land as quickly as possible. If you receive an approach and you have no departing traffic, you should give them clearance to land directly with the initial call. A pilot must have their **landing clearance at the latest before crossing the runway threshold**. If they don’t have clearance then, they will go around on their own. The approach controller is responsible for the separation between approaches until the runway threshold is crossed. At international airports (EDDx), however, you as the tower controller may "save" the separation with the help of speed restrictions if you notice that without them, a LOS would become probable. You can also use speed instructions to maintain a gap for a VFR pilot, for example. However, it is important to coordinate speed instructions with the approach controller if there is another aircraft behind the aircraft with the assigned speed. If two approaches are so close that there is still a risk of a loss of separation, you must instruct one of the aircraft (usually the following one) to go around **before(!)** the loss of separation occurs. In addition, traffic information about the traffic concerned can be useful. Further information on handling missed approaches can be found in the [corresponding chapter](https://knowledgebase.vatsim-germany.org/books/practical-procedures/page/missed-approach-controller-guide "Missed Approach - Controller Guide").A turn below the MVA without the above mentioned addition is a serious, safety-relevant issue and will lead to a fail in exams.
##### **3. Coordination with Approach / other stations** - Every missed approach must be coordinated with the approach controller (if online). Verbal coordination should always be preferred, as labeling the tag alone is often lost. Example: "*Pickup North, Tower - Go ahead - Missed approach Asiana 541, Runway 25L, flying \[standard missed approach / Heading 220 due to United taking off etc.\]. I don't know the reason yet. - Roger, send him to 125.355*" ##### **4. Ask the pilot for the reason and send him off** - If the reason for the missed approach was not obvious (e.g. not instructed by the controller), the controller should ask for it. ("DLH123, report reason for missed approach"). The reason may be relevant for other air traffic (e.g. windshears - this information should definitely be passed on to following pilots) or may be of a technical nature (e.g. problems with the engine, landing gear, etc.), as a result of which the aircraft should be given priority for the next approach or be treated as an emergency if applicable. - As soon as the aircraft is clear of all other traffic and some time has passed since the initiation of the missed approach, the aircraft is sent away to the approach controller. ##### **5. Pass on the reason to the APP** - As mentioned above, there can be many reasons for a missed approach which are also important for the approach controller to know. Therefore, the reason should be forwarded to the APP controller so that he does not have to ask the pilot about it again. # Deicing using the example of EDDM ### Introduction Aircraft are becoming more and more sophisticated and complex, there are more and more plugins that are close to reality and there is more and more interest in implementing real procedures - that's why we want to deal with the topic of "deicing" here. First of all, this is more of an "eye opener" to shed light on this topic, which is actually very interesting but has been unfairly underappreciated. As we have to go into more detail here, the text will be a little longer. ### General #### #### What is deicing and why is it important? Frost, snow, ice and other contamination have a considerable influence on the aerodynamics of an aircraft. Just a few millimetres of contamination / ice on the upper surface of the wing can significantly influence and even disrupt the airflow and thus impact flight characteristics. Many aviation disasters are related to icing (just search for "aviation incidents / crashes deicing" on Google). Deicing can be done mechanically (e.g. using a broom / shovel to remove snow from the wing surface) and chemically (i.e. with deicing fluid using deicing vehicles). #### When do you de-ice? Only in snowy conditions, right? There are many reasons that make deicing necessary. Very often deicing is needed even though it is not snowing at all, possibly even when the sun is shining. Here is an example: You arrive in Munich after a 6-hour flight and still have cold fuel left in the wing tanks, which are at -40°C or colder. At the turnaround you refuel for the next leg of your flight, it is +6°C in Munich and cloudy, sometimes the sun is even shining. What happens now? The warm, new fuel enters the tanks, hits the still very cold wing and a layer of clear ice forms on the top of the wing, the so-called "cold soaked wing effect" has occurred. Since, as mentioned above, contamination of the aircraft parts is not at all compatible with the aerodynamics of the aircraft, deicing can be necessary in sunny/cloudy conditions and at temperatures way above 0°C. #### Who decides when to de-ice? Who actually de-ices? Who has the final say? First of all, the PIC (Pilot in Command). They are responsible for the safety of the flight and so they decide whether to de-ice or not. Whether the wing is completely free of contamination and looks brand new and they still want to de-ice is up to them. Even if, as has unfortunately happened often enough, a rolling igloo taxis towards the runway, deicing is still the pilot's (...or the airline's financial situation...) decision. However, as soon as an aircraft has registered for deicing, deicing is carried out by the respective airport operator or the handling agents. They alone then decide WHAT is de-iced on the aircraft and HOW. They are the last ones who inspect the aircraft and therefore assume liability / responsibility. They act according to the "CAC - clean aircraft concept", i.e. the aircraft must have been freed of any build-up and contamination after deicing. So even if there are only a few small snow residues on the fuselage of the aircraft, the entire fuselage (or at least parts of it) is de-iced, even if the PIC decides against it. He has no authority whatsoever (with the exception of technical backgrounds for special aircraft types / restrictions). #### How is deicing carried out (using Munich EDDM as an example)? A distinction is made between 1-step deicing and 2-step deicing. In 1-step deicing, a mixture of type 1 fluid and very hot water at almost 80°C (type 1 is always orange in color) is applied to the aircraft, contamination is removed and at the same time a protective layer is applied to prevent re-icing. In 2-step deicing, the contamination is first removed from the aircraft with type 1 and then "anti-iced" or protected in the 2nd step with type 4 fluid (cold, not heated, green in color and rather viscous). #### What is Holdover time? The holdover time, or HOT for short, is the period of time during which the aircraft is protected from re-icing. Depending on the type and method of deicing, the weather conditions, the type of aircraft (classically mainly aluminum, e.g. B737, or increasingly composite materials, e.g. B787), the deicing process used, etc., this can range from just a few minutes to several hours. Once the HOT has expired, there is no longer any reliable protection against contamination. Every (sensible) pilot will therefore want to de-ice again. However, the pilots themselves have leeway here and can still take off at their own discretion. #### #### Where is deicing carried out? In Munich, deicing takes place directly on the deicing pads/areas, which are located directly at the holding points in front of the respective runways. This concept makes Munich almost unique in the world (more on why this is so ingenious and why it is mentioned separately in a moment). There are typically 3 deicing pads per active runway. In other words, for 08 operations, the intersections A1/A2/A3 at 08L are/can be used for deicing, and B1/B2/B3 at 08R. The holding points are simultaneously the deicing pads (08L A1 becomes deicing pad 1, A2 becomes deicing pad 2 etc. ... ) The same is true for 26 operations: Here there are A13/A14/A15 in the north which become the deicing pads DA13/DA14/DA15. In the south, simultaneously B13/B14/B15 etc turn deicing pads. Incidentally, you will find these on the ground charts as "DA14" = DeicingArea 14. Propeller machines without prop brake are deiced in position, i.e. they receive apron deicing. #### #### Why is deicing directly at the runway so efficient? We learned above that the holdover time starts as soon as the deicing procedure begins. This is where the clock starts ticking. At airports with so-called apron deicing procedures, the clock starts ticking with the deicing procedure in the aircraft’s parking position. Then, the pilot still has to push, may additionally suffer a delay due to taxiing traffic and then we are looking at 10-20 minutes taxi time to the runway and possibly even more waiting time at the holding point. This time is wasted unnecessarily and minimizes our HOT. The advantage of remote deicing (i.e. at the holding points) is that you can taxi to the CAT2/3 holding point immediately after deicing, do the engine runup (should be done after deicing) and take off directly. This minimizes time losses and the chance of having to de-ice again due to expired HOT is very small. #### Another advantage (even if completely unnecessary on VATSIM) In Munich, there are collecting tanks underneath ALL deicing pads. The deicing fluid / snow drains into these collecting tanks through small grooves on the deicing pad. The deicing fluid is collected, treated and can be reused, and up to 70% of deicing fluid can be completely reused. This saves a lot of money, protects the environment and the waste heat generated is used to heat an entire terminal. Pretty ingenious! #### #### I want to de-ice! Where do I have to register? In reality, there are many different ways to do this. Normally, pilots call in at least 20 minutes before TSAT (Target Startup Approval Time) on 121.990 Mhz (callsign "Munich Deicing Coordinator") and register there for deicing. The coordinator sees all information about the flight on their system and confirms the registration by radio. Depending on the airline, it is also possible to register for deicing via ACARS, but we are not (yet?) able to do this on VATSIM. Alternatively, you can call Tower, Ground, Delivery, Handling Agents etc. directly. #### So how is deicing handled on VATSIM? You call in at Delivery or the lowest position responsible for you and register for deicing in advance.| Station | Phraseologie |
| **Pilot** | München Delivery, DLH4YA, require deicing before departure. |
| **ATC** | DLH4YA, request confirmed, you are in the sequence for deicing. |
| Station | Phraseologie |
| **Pilot** | Tower Servus, DLH4YA, Entry S8 for deicing. |
| **ATC** | DLH4YA, servus, taxi deicing area B15 via S, on second radio contact decing crew on XXX,XXX Mhz, report deicing completed. |
1820Z EDDM 26015KT 2000 -SN BKN006 OVC020 M02/M04
In short (and only very roughly!), weather report from 18:20 Zulu (i.e. in the evening), from Munich, wind from 260 degrees at 15 knots, 2000m visibility RVR, light snowfall, cloud cover at lower limit 600 ft, closed cloud cover lower limit 2000 ft, temperature -2°C, dew point -4°C. Now I already know we don't have "active frost" alone where we can only deice / anti-ice 1 step with type 1, but we have evening / darkness, low visibility due to snowfall and sub-zero temperatures. Since we only have RVR values (in real life we use the MOR meteorological observation range), we go directly to Table 42: SNOWFALL INTENSITIES AS A FUNCTION OF PREVAILING VISIBILITY. We know it is evening, so we go to the left column under "Night". We also know it is currently -2 degrees, so we go to the "colder/equal -1" column. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2022-10/edmm-deicing-vischart.jpg) Now we take the reported visibility of 2000 m and look at the top of the column where we have to position ourselves. In our case at 1 1/4 (2000). Well, one finger to the left, one finger from above, put the two together and we end up with the value "MODERATE". Quite simple, isn't it? With this "MODERATE" value in mind, we now go over to Table 27: Type IV HOLDOVER TIMES FOR CLARIANT SAFEWING MP IV LAUNCH (This is the deicing fluid type 4 with a concentration of 100%, which the deicing coordinator told us is what they used). [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2022-10/edmm-deicing-hottyp-4.jpg) Now we continue as before: We know in the left column at "Outside Air Temperature" we have 2°C, ergo we are at "-3°C and above". We also know that the concentration is 100% type 4, so we go to "100/0" in the column. We have previously picked out the visibility and the respective value, which was "MODERATE" and slide into the respective column to "MODERATE SNOW; SNOW GRAINS OR SNOW PELLETS"..... and get a value of 1:05 - 1:45. This means that as soon as the anticing starts, i.e. the first contact with type 4 on the aircraft, we now have a holdover time of between 1h:05 min and 1h:45 min. This will get you out of ATC pretty reliably and you still have a good time buffer. So it wasn't that difficult after all ;-) I have attached the tables, if you want to read a bit yourself just search for the "FAA2020-2021 Holdover Tables". This should give you a rough insight into the world of de-icing, why it is so important, what is behind it, how it roughly works and what approximate processes are behind it. Xplane, FSLabs and the Majestic Dash Q400 already simulate icing, GSX and Co. allow you to de-ice yourself and the developers of aircraft are picking up this topic more and more. We (RG Munich) are always happy to answer any queries, suggestions, technical questions or discussions! This thread may be expanded if necessary. Spelling mistakes and other errors can be collected and exchanged for an ice cream. ### Epilog This article was created by Florian Weingartner, RG Munich, who kindly agreed to transfer it to the Wiki. # Low Visibility Operations (LVO)The correct use of LVO is not a mandatory part of S1 training.
#### Introduction In normal operations, pilots fly an ILS approach up to the so-called CAT1 minimum which usually sits 200ft above the runway threshold. Not later than at the minimum, the crew must have certain runway markings or the runway lighting in sight in order to be able to continue the approach. If this is not the case at the minimum, the aircraft must go around. ILS (and more recently also GLS/GBAS) CAT2 and CAT3 approaches are therefore available for poor weather conditions. In order for these to be carried out, the aircraft requires certain equipment (e.g. a radio altimeter), the crew must be trained and approved for this and the airfield must have a correspondingly precise and approved ILS system. In addition, the provision of CAT2 and CAT3 procedures requires certain operational procedures on the part of air traffic control and the aerodrome operator. These are explained in the following chapters. If CAT 2/3 procedures are activated, this is referred to as **Low Visibility Operations (LVO)** or **Low Visibility Procedures (LVP)**. #### Requirements and activation LVPs are active as soon as one of the following two criteria is met - Ceiling < 200 feet - Runway visual range (RVR) <= 600 meters The ceiling is the lowest cloud base with a coverage of more than 50%, i.e. BKN or OVC. Sometimes no cloud base can be measured (e.g. due to dense fog). In this case, the vertical visibility is used. This is given in the format VVxxx. Here are a few examples: - VV010 = vertical visibility 1000 feet - VV002 = vertical visibility 200 feet - VV/// = Vertical visibility not measurable. This value is to be interpreted as vertical visibility less than 100 feet The runway visual range is a value determined by a measuring system that differs from the ground visibility determined by a weather observer. In terms of horizontal visibility, only the RVR is relevant for the provision of LVOs. Further information on RVR can be found [here](https://en.wikipedia.org/wiki/Runway_visual_range). The following rules apply to airports with several runways: LVOs always affect the entire airfield. Even if the RVR is well over 600 meters on one runway but 550 meters on the other, Low Visibility Procedures apply to all runways and taxiways. #### Measures for LVO ##### Switch ATISCorrespondingly, during LVP the runway is only considered vacated by an arriving aircraft when the aircraft is completely behind the CAT 2/3 holding point. Otherwise the runway is not considered clear in terms of separation.
At some airports, the Landing Clearance Line (LCL) procedure is permitted. In this case, the runway is considered cleared when the aircraft has completely overrun the so-called landing clearance line (usually located 102 m from the center of the runway). This procedure is sometimes even more restricted (e.g. only for WTC M or L). Details on whether the procedure is permitted at your airfield, where the landing clearance line is located and how to work with it can be found in the SOP of your training airport. Important: Depending on the SOP of the respective airport the sensitive area must be clear when the next approach reaches the 2-mile final approach. If the sensitive area is not clear when the following approach is at 2 miles, the approaching aircraft must be instructed to go around. When using the Landing Clearance Line procedure, the Landing Clearance Line must be crossed before the following approach is at 0.6 NM final approach or 200ft AGL. Whether these procedures are used on Vatsim can be found in the respective tower SOPs. ##### Tell the RVR Not every RVR allows for legal landings. This depends on various factors. These include the certification of the airline, the aircraft, the crew, but also the type of approach. In order for a pilot to know whether he is currently still allowed to land, he must receive the latest RVR at two points in time: - At the approach clearance (by the approach controller): "DLH123, cleared ILS approach runway 25L, RVR 800 meters" - Before the 4 NM final approach again (can also be given with the landing clearance): "DLH123, RVR runway 25L 600 meters, wind 210 degrees, 4 knots, runway 25L cleared to land" As there is no source for live RVRs on VATSIM, the RVR is read out of the METAR instead. Sometimes it is also possible that there is only one RVR for the opposite direction (e.g. 08R instead of 26L) in the METAR. This is then used. If there is no RVR at all in the METAR for a particular runway, it can be assumed that the RVR is greater than 2,000 meters. ##### Discontinuation of certain procedures Some procedures depend on aircrafts’ visual contact or that the tower controller sees the aircraft from his window. We also simulate this on Vatsim in good weather. However, at least under LVO, the visibility is so poor that the following procedures are no longer permitted: - Conditional line-ups - Multiple line-ups - Reduced runway separation (limits are already higher) - VFR / SVFR (limits are already higher) - exception: pilot confirms that he is simulating VMC - Visual separation in the vicinity of aerodromes - Taxiing on unlit taxiways (if explained in the airport's SOPs) Furthermore, instructions such as "Expedite taxi" or "Expedite vacating the runway" should be avoided, as it is generally not possible for the pilot to taxi faster due to poor visibility. # Approach # Radar Vectors ‘Radar vectors’ just means that an aircraft is guided by the air traffic controller through specific headings. In contrast to a standard IFR procedure (STAR, SID, Standard Approach), a so-called Minimum Vectoring Altitude (MVA) must be adhered to. This is specified for certain precisely defined areas and guarantees an obstacle clearance of at least 500 ft and sufficient radar and radio coverage. The MVA areas can be displayed in Euroscope. Values in brackets apply to the winter months. Radar vectors can be given as heading (e.g. heading 210) or as relative turn instruction (e.g. right/left by 10 degrees). The latter should only be used if there is not enough time to request a heading. Otherwise, always work with headings. If a radar vector is not self-explanatory (e.g. for final approach), the reason should always be given (for separation, for spacing, etc.). Particular care must be taken when an aircraft is in a turn. In this case, requests such as: "Turn left/right by..." are completely pointless, as the aircraft in the turn can not know which heading this instruction refers to! If it is important that the aircraft turns immediately to a specific heading, the following phrase is a good idea: > DLH123 stop turn heading 180 Radar vectors for an ILS approach or localizer should be given with a heading within 30° to the final approach course. Example: Runway direction 26 - Heading for intercept 230° or 290°. **A clearance for an approach does not cancel a previously assigned speed!** A new speed assignment must be explicitly communicated to the pilot. > DLH123 resume normal speed, turn right heading 220, cleared ILS 26R. > DLH123 turn right heading 230, cleared ILS 26R, maintain 220 kts to 10NM final thereafter 170 kts until 5 miles final. The end of a STAR is the IAF, which also includes a holding pattern. This IAF automatically is the clearance limit for the approach unless the clearance limit is specified earlier in the charts. If the pilot receives no further instructions on what to do before reaching the clearance limit, he must enter the holding pattern. It is therefore a good idea to instruct the pilot on what to do after the last waypoint as soon as the initial contact is made. The clearance to a transition waypoint (e.g. DM427) includes the clearance to continue flying the transition. > DLH123, identified, leave ROKIL on Heading 120, expect ILS 26R. This prevents the pilots from calling when the frequency load is high and demonstrates good proactive planning! If you want to turn a departure away from a SID, you must note that for noise protection reasons this is only permitted in Germany above 5000 ft AGL for jets and 3000 ft AGL for props. Below MVA it is totally prohibited.**Tip:** A quick note on intercept headings: If strong northerly or southerly winds are known to be present, it is sometimes worth adjusting the course accordingly, i.e. shifting it by 5° or even 10°. Otherwise the pilot flying into the wind may not reach the landing course before the glide path. It makes sense to ask two or three pilots for a wind check at the beginning. Pilots seem to be flying less and less with extremely different winds in recent years (at least it feels like it). It's the exception rather than the rule and requires a little sensitivity in case someone has the wind from somewhere completely different.
### Further links - **Skybrary:** [Basic Controller Techniques - Vectoring](https://www.skybrary.aero/index.php/Basic_Controller_Techniques:_Vectoring) - **Skybrary:** [Vectoring Geometry](https://www.skybrary.aero/index.php/Vectoring_Geometry) - **Skybrary:** [Conflict Solving](https://www.skybrary.aero/index.php/Conflict_Solving) - **Skybrary:** [Basic Controller Techniques - Vertical Speed](https://www.skybrary.aero/index.php/Basic_Controller_Techniques:_Vertical_Speed) # Speeds Used sensibly, speed control is a very helpful tool for separating aircraft and maintaining sequences. ### Types of speeds A distinction is made in aviation between different speeds: - **IAS (indicated airspeed):** The speed displayed to the pilot on the airspeed indicator. It is decisive for the aerodynamic behavior of the aircraft, i.e. how many air molecules actually flow around the wing and generate lift. In powered flight, it is generally indicated in KIAS (knots indicated airspeed) (kts=NM/h) - **TAS (true airspeed):** The speed actually flown, i.e. the relative speed of the aircraft in relation to the surrounding (still) air. The discrepancy between IAS and TAS therefore increases as an aircraft flies higher, as the air becomes thinner and thinner and the aircraft must fly faster and faster in relation to the TAS so that the IAS remains constant, i.e. the same amount of air molecules flow around the wing per unit of time. It is specified in KTAS (knots true airspeed). - **GS (Ground Speed):** The speed of the vertical projection of the aircraft onto the earth's surface. This is therefore the TAS with the wind influences factored in, which cause the aircraft to fly slower over ground than the TAS if there is a headwind and faster if there is a tailwind. This is the speed displayed to the controller on the radar. - **Mach Number:** Percentage of the speed of sound. Indicated with a dot and the percentage, e.g. "Mach .80" = 80% of the speed of sound. The Mach Number depends on many values, such as air density and temperature.Similar to the rule of thumb for descents (1000 ft in 3 NM), speed reduction is approximately 10 kts in 1 NM.
### Using the different speeds **Below FL280**, the **Indicated Airspeed (IAS)** is used, as it is responsible for the aircraft’s aerodynamic behavior. **Above FL280**, the **Mach number** is generally used, as the aircraft then become so fast that the upper limit of the possible speed is no longer determined solely by aerodynamic aspects, but also by the so-called "critical Mach number". This is the Mach number at which the first effects of supersonic air flow occur on the aircraft, causing not only turbulence but also decreasing controllability of the control surfaces. The higher the aircraft climbs, the lower its maximum IAS becomes, while the Mach number remains the same. If speed control is used for descending aircraft, IAS can and must be used above FL280, which might easily happen at e.g. FL340. Depending on the aircraft type, the "switching altitude" between IAS/mach/IAS can also be above or below FL280.A change of **Mach 0.01** causes a change in **TAS** of about **6 kts**.
If necessary, the following phraseology can also be used. However, you must be aware that not every pilot will understand this instruction! > DLH123 maintain Mach decimal 80, on conversion 320 knots Some example values at which FL is switched from IAS to Mach:| **Mach** | **IAS** | **Conversion FL** |
|---|---|---|
| **.82** | **310** | FL303 |
| **.82** | **280** | FL350 |
| **.82** | **250** | FL399 |
| **.78** | **310** | FL278 |
| **.78** | **280** | FL324 |
| **.78** | **250** | FL374 |
| **.74** | **310** | FL250 |
| **.74** | **280** | FL299 |
| **.74** | **250** | FL350 |
A detailed explanation of the rules of thumb is available as a video [here.](https://www.youtube.com/watch?v=NB6cMrjQHxE "Speed Control - Rules of Thumb")
##### Example We have aircraft A and aircraft B at the same altitude, both leaving the sector at point P. *Aircraft A still has 150 NM (20 minutes) to point P. Aircraft B still has 146 NM (19 minutes) to point P.* We want a separation of at least 7nm at point P. We already have a separation of 4nm, so we need to achieve a separation of an additional 3 NM (7 NM we want minus 4 NM we already have) in 20 minutes. Now we calculate how many kts GS difference we need between the planes to reach this distance. Since the speeds are per hour, we now extrapolate this to 60 minutes. *60 minutes / 20 minutes = 3* *3 NM spacing \* 3 = 9 NM spacing* *Since we know that 1 KT GS = 1 NM per hour, we now know that we need a speed difference of 9 KT GS to achieve a distance of 3 NM in 20 minutes* We know 0.01M ~ 6 KT GS, so in this case we need a Mach difference of 0.02M, which will be a difference of 12 KT GS, this will lead to 4nm more difference in 20 minutes, therefore leading to a total of 8 NM (4 NM current distance + 4 NM new distance due to speed difference) distance at point P. If the aircraft are not at the same altitude, we must subtract 6 KT per 1000ft from the speed delta if the higher aircraft is the leading one. If the higher plane is following, we have to add 6 KT per 1000ft to the speed delta. #### Distance after a certain time If speed control is used, the distance after a certain time can easily be calculated:Spacing = Speed difference / 60 per minute
As a rule of thumb, a speed difference of 30 KT (e.g. 250 KT and 280 KT) over a distance of 30 NM gives a spacing of about 3 - 3.5 NM. ##### Example If the preceeding aircraft flies 30 KIAS more than the suceeding, this results in a spacing increase of half a NM per minute! Be careful if the preceedingaircraft is significantly higher than the suceeding! Remember that the TAS decreases the lower the aircraft flies. It is therefore possible that the suceeding aircraft is already flying 30 KIAS slower than the preceeding aircraft, but is still faster in relation to the GS, precisely because it is higher. It is therefore a good tactic to bring the aircraft that you want to fly slowly to the desired altitude first and then reduce the speed. If you want to maintain a high rate of descent, it is of course difficult to radically reduce speed. This should be taken into account! When approaching an airport and holding is expected, the phrase "Reduce Minimum Clean Speed" is often used, i.e. the request to reduce to the lowest possible speed without setting the flaps. It should be noted that such a speed can always vary depending on the aircraft type and load. It can therefore not be used as a basis for relaying. The phrase "Reduce Minimum Approach Speed" should not be used! The following rule applies on the final: On the way to the 10 NM final point, approx. 1 NM spacing is lost because the front aircraft reduces earlier. The same applies at the outer marker. You should therefore aim for minimum separation + 2 NM when vectoring so that the separation remains sufficient until touchdown! ### Advanced: Ground speed effect First of all, we need to take a look at the different speeds. The pilot has his indicated airspeed (IAS). The controller has the groundspeed (GS). The connecting element is the true airspeed (TAS). The IAS is only an indicator of how fast the aircraft is currently moving through the air. The GS is an indicator of how fast the aircraft is moving relative to the ground, corrected for influences like air density, wind, etc. This speed corresponds exactly to the speed a car would have on the ground. The TAS is a bit tricky. It expresses the speed that a solid body has in a certain medium. If we ignore the wind , we only have to deal with the solid body (our aircraft) and the medium (air) in which it is moving. At high altitudes, the air becomes thinner. This means less resistance from the medium, which leads to a higher speed of the solid body. The conclusion: the higher the aircraft, the greater the speed. These speeds are all interrelated. The TAS can be determined using a simple formula. The groundspeed is known to the controller, the indicated airspeed must be requested from the pilot.TAS = IAS + FL / 2
##### Example Let's assume that approach has received two aircraft as a package from center. Both are on the same STAR at different altitudes and there is not enough space to separate the aircraft laterally. Our scenario is as follows: **DLH123 at FL150 / 300 KIAS - CFG999 at FL160 / 300 KIAS**, same lateral position, same flight direction. We now need them both at 5000ft and 3NM separation within 40NM using vertical techniques only. We assume that there is no wind, so GS = TASTAS DLH123 = 300 KT + 150 / 2 = 375 KT TAS CFG999 = 300 KT + 160 / 2 = 380 KT
We need both aircraft at 5000 ft, so for DLH123:TAS DLH123 = 300 KT + 50 / 2 = 325 KT
This leads to a speed difference between the aircraft of 55 KT (380 KT - 325 KT), so that the lateral separation increases by about 1 NM per minute (55 KT / 60 minutes). We therefore need three minutes to separate the aircraft at the speed difference of 3 NM. We must let both aircraft descend simultaneously and one must reach our target fix three minutes before the other. What must the descent rates be in order to achieve this? First, we calculate the descend rate of the higher aircraft. This moves at 380 KTS GS. It needs approx. 6 minutes for the 40 NM (40 NM / (380 KT / 60 minutes)) and must lose 10,000ft. This leads to a sink rate of 1700 ft/m. DLH123 also needs 6 minutes at its current altitude and speed, but has to be there 3 minutes later than the higher CFG999. So it has to lose the 11,000ft in 3 minutes (6 minutes total flight time and the 3 minutes needed to increase separation leaves 3 minutes for the descent). This means a descent rate of about 3600 ft/m ### Further links - **Skybrary**: [Basic Controller Techniques - Speed Control](https://www.skybrary.aero/index.php/Basic_Controller_Techniques:_Speed_Control) - **Youtube**: [Enroute Speed Control](https://www.youtube.com/watch?v=-Uwe1vjaDCw) (LOVV FIR) - **Youtube**: [Speed Control - Rules of Thumb](https://www.youtube.com/watch?v=NB6cMrjQHxE&) # Establishing approach sequences This guide is intended to provide new approach controllers with an easy introduction to the subject. It contains the basic principles and important tips for establishing sequences on the final approach. Detailed knowledge of the articles "Radar vectors" and "Speeds" is assumed. ### General #### Terms **"Separation"** refers to the minimum distance that two aircraft must have to each other vertically and/or laterally. Radar separation and wake turbulence separation are particularly important in this guide. **"Spacing"** refers to the distance that you want to achieve between two aircraft on the final approach. This depends on many factors such as the weather, the current traffic situation, the airfield and the quality of the pilot. In an approach sequence, we always work towards achieving the desired spacing while maintaining separation. **"Compression":** As a controller, we always plan in such a way that separation is maintained until touchdown. So if we tell the pilot in front to maintain 170 kts until 5 NM before the runway, they will reduce to their final speed from this point on. In the meantime, however, the aircraft following them continues to fly at 170 kts and consequently will start to catch up. We refer to this phenomenon as "compression" or "catch-up". In most cases, it is sufficient to add one mile to the required separation to counter compression. An example: due to the aircraft types, we need 5 NM wake turbulence separation between two approaches. We therefore add 1 NM and arrive at our spacing of 6 NM, which we maintain until 5 NM before the runway. #### Finding the correct spacing In addition to the criteria mentioned above, there is a lot more to consider in order to find the correct final approach spacing. This includes, for example - The layout of the airport and runway(s) - How many runways does the airport have? Are they used for landings only or for take-offs as well? Does the runway have "high-speed exits" that allow pilots to quickly leave the runway? - The current traffic volume - are there currently more inbounds or outbounds? Communication with the tower is required here! - The weather - Are LVP in effect? - Pilots - If, based on your experience, you don't trust a pilot to leave the runway quickly enough, give the following pilot an extra mile. A go-around is always more inefficient than an extra mile. - Experience - Keep a constant eye on the situation on the ground. If the tower repeatedly fails to use a gap of 5.5 NM for a departure, give the next aircraft an extra mile. As a general rule, a gap of 6 NM (+1 NM compression = 7 NM final approach spacing) is sufficient at most airports to allow a departure to take off. ### Practical implementation Now we have to put all this into practice. #### Speed Control Especially while starting out, It is generally advisable to set all aircraft in your TMA to a uniform speed as the work/traffic load increases. 220 kts is a good speed for this, because almost all aircraft can fly this "clean" (without flaps/slats). If all pilots are flying at the same speed, it is much easier for you to develop a plan because you can recognize the gaps laterally on the scope. In order to allow the pilot a reasonable speed reduction, the pilots should preferably not be faster than 200kts when they reach the glideslope. Important: The approach clearance does not cancel the speed reduction. However, this is not the case everywhere. So if you are unsure whether the pilot knows this, it may be better to give them the speed again instead of finding out later that the pilot has already reduced their speed. On final, the most commonly used values are **180 kts to 6 NM / 170 kts to 5 NM / 160 kts to 4 NM**. Note: 180 kts to 6 NM in particular can lead to a less precise final approach, as pilots with different types of aircraft reduce to their final approach speed at different speeds. They will then fly even longer at different speeds than at 170 kts to 5 NM or 160 kts to 4 NM and in the end, this can lead to a difference of 0.3 - 0.4 NMSo remember: As soon as you realize your airspace filling up and you can no longer get all the planes onto the approach directly, reduce all planes to one speed early on. Try to stick to the "standard speeds", especially at the beginning, and only reduce them as you gain experience (if at all).
#### The correct altitude It is also very important to descend in time. You should calculate that an airplane can descend 300 ft per NM (~1000 ft per 3 NM). As a rule of thumb, if the airplane is guided over the downwind, it should not be higher than 8000 ft abeam of the field, otherwise it is clearly too high to turn it to a 10 NM final. If you realize that the pilot is too high for your further planning, there are several ways to counteract this. You could tell the pilot the rough distance they still have to fly (see also the next chapter) so they can then descend faster or slower at their own discretion. Otherwise, you can also assign the pilot a certain descent rate. But don't wait too long, because even with speedbrakes, aircrafts’ descent rates are not limitless. With the clearance for the approach, pilots may descend to the published altitude for the approach. If the controller wants the pilot to fly at a different altitude for the approach, this must be explicitly stated. #### Achieving the desired spacing To estimate the distance of the aircraft until touchdown, observe a plane that is already on the ILS. Then, you need to determine the spacing you currently need. If, as in the above example, you need a final approach spacing of 7 NM, start with the first aircraft and count backwards in increments of 7. So, if the first aircraft is at 13 NM, the next one, at the same speed, must fly exactly 7 NM more (i.e., 20 NM). The ones behind will need to fly 27, 34, 41 NM, etc. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2024-02/distancemeilen.png) There are various ways, procedures, and tips to achieve this: ##### Downwind The downwind leg runs parallel, in the opposite direction to the final approach, and should be about 5 NM away from it. Many airports already have arrivals or transitions set up like this. The planes should not exceed 220 KIAS to avoid overshooting when turning onto the final approach. If you turn the following aircraft when the preceding one (already established on the LOC) is abeam, this will result in a spacing of 5.5 to 6 NM between the two aircraft on the ILS (Figure 1), assuming both aircraft have the same speed. This refers to the moment when the aircraft turns, not when you as the controller start speaking – you need to issue the instruction a bit earlier. If you turn the aircraft when it's 0.5 NM past abeam, you will gain an extra NM of spacing because the aircraft must "fly back" that 0.5 NM (Figure 2). Each additional NM of downwind results in 2 NM more flying distance. Turning the aircraft when it's 0.5 NM before abeam will result in 1 NM less spacing. With this rule of thumb, you can calculate any desired spacing. Experiment a little and fine-tune with earlier or later speed reductions. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2024-02/6meilen.png) *Figure 1* *[](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2024-02/61meilen.png)* *Figure 2* If the aircraft is turned onto the final approach just two radar updates (10 seconds) later than planned, it will have already covered 1 NM in that time. This means it will need to fly 2 NM more, which is rarely corrected with speed adjustments. Over 30 seconds, this results in 6 NM more flying distance and reduces the runway capacity by 50%. This example clearly shows why your **priority should always be the final approach**! ##### Base You can use the base leg depending on local conditions and traffic to turn aircraft from the downwind onto the final approach (Figure 1) or to allow aircraft to fly more or less "directly" onto the final approach (Figure 2). [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2024-02/base3.png) *Figure 3* [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2024-02/base1.png) *Figure 4* If you look closely at the figures, you'll see that the distance of BCS2458 (and EWG5AM in Figure 2) relative to the final approach remains constant. The only variable distance is that of the Lufthansa moving westward toward the runway. Therefore, the base leg should ideally be at an angle of 90° or more to the final approach in both cases. Otherwise, situations like in Figure 5 can occur. Here, the distance from DLH5GX to the runway decreases, while the distances of BCS2458 and EWG5AM increase. With each radar update, the spacing relative to the approach changes. This makes it much harder to accurately turn the aircraft one after the other onto the final approach. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2024-02/base2.png) *Figure 5* ##### Final Approach The goal of the approach controller should be to guide all aircraft onto the final approach at more or less the same point. To achieve this, it’s important that the feeder receives neither too few nor too many aircraft. In the first case, the intercept point shifts closer to the airport; in the second case, it shifts farther away. Of course, you won’t always manage to have every plane intercept at exactly the same point. However, at most German airports, 10-15 NM is a good guideline. Generally, on Vatsim, the goal should be to have as short a final approach as possible, as this minimizes the effects of technical differences, such as wind or speed variations. ### Adjustments #### Slow aircraft One of the more challenging situations is when you need to integrate an aircraft into the sequence that will fly the final approach significantly slower than the others. Here, too, you should try to let the plane fly **as short a final approach as possible**. Over 20 NM, a speed difference of 60 or more knots will waste much more space than over 8-10 NM. Therefore, the aircraft should always be kept near the ~10 NM final, for example, by having it fly circles. When the opportunity arises, you can then slot it in. How many miles do you need to the next aircraft? You can calculate this again using the formula:Speed difference / 60 = loss of spacing per minute
For example, if the slow type is flying the ILS at 120 KTS and cleared for an 8 NM final, it will take about 4 minutes to reach touchdown. If the following traffic is flying at an average of 180 KTS, it gains 1 NM per minute on the slow type. Therefore, the following plane needs at least 4 NM more than the required separation to avoid catching up to the slow aircraft. In such a scenario, it’s always better to err on the side of caution and give one or two miles more rather than too few. A further video with an interesting approach can be found here: [https://youtu.be/VNcSB-c6atU?si=Wo2vHTW9Dgm0zHE6](https://youtu.be/VNcSB-c6atU?si=Wo2vHTW9Dgm0zHE6) #### Wind Wind can also affect the headings used for downwind or base legs. For an east-west runway with a west wind pushing aircraft eastward, a heading of 360° for the base leg may need to be corrected 5 or even 10 degrees to the left. A heading of 180° may need to be corrected to the right. Tools like windy.com, which show the wind at altitude, can help assess the potential effects. In cases of strong headwind on the final approach, it’s important that aircraft are not turned too early or too late onto the final. As soon as the aircraft turns onto the intercept heading, its ground speed begins to decrease. If the trailing aircraft is turned too early, speed control will be less effective than in calm wind conditions. If the aircraft is turned too late, it becomes much harder to make up the gap with a headwind, and the aircraft will fly more distance in the final turn. Think about the effects of wind when it’s perpendicular to the approach (e.g., from the north or south on an east-west runway). What difference does it make on the base leg when aircraft from one direction have a tailwind and others a headwind, even if all are flying at 220 kts? Consider, before logging in, what adjustments might be sensible and observe how it works with the first few aircraft. #### Pilots With some experience, you can usually gauge whether a pilot is new and/or unfamiliar with their aircraft from the first contact. Keep this in mind when planning and issuing instructions. Give a new pilot an extra mile or two on the final, keep in mind that their instructions may be carried out with some delay, and don’t waste time scolding them for mistakes. Focus instead on resolving the situation. Not everything is lost because of one pilot! # Holding Management There can be various reasons why you have to initiate a holding. One reason can be that the arrival controller can simply no longer manage to get the necessary spacing between arrivals rushing in. Holding is then used as a means of creating spacing. Another possible reason is that the approach controller stops accepting any more aircraft because, for example, the runway is closed. ### Initiating a holding pattern Holding is always managed by the CTR controller. If you know that you have to initiate a holding pattern, you usually slow down all aircraft still flying towards the holding fix to "minimum clean speed" so that they have to spend as little time as possible in holding. This is more economical. It is important to make sure that all aircraft arrive at the holding fix with a 1000 ft separation, so ideally you would work with rates in descent. > HOLD AT / OVER (significant point, name of facility or fix) MAINTAIN / CLIMB / DESCEND (level) \*(additional instructions, if necessary)\* EXPECT FURTHER CLEARANCE AT (time) / IN (minutes) / EXPECTED APPROACH TIME (time) The pilot should always be informed where and how high to fly into the published holding pattern. In addition, an expected approach time (EAT - Expected Approach Time, i.e. time when to leave holding) must be calculated if a stay in the holding patternof more than 20 minutes can be expected and be communicated to the pilot together with the holding instruction. For military aircraft (1-2 seater jets), the EAT must always be added regardless of the 20 minutes, as they generally calculate their fuel very tightly and may have to divert directly to the alternate. In addition, the pilot must always be informed if a new EAT deviates from the previous one by 5 minutes or more. > DLH123, hold over SPESA, maintain FL130, expected approach time 1230. In addition to the ‘general holding instruction’ shown here, there is also a ‘detailed holding instruction’. This contains the following points: 1. holding fix 2. holding level 3. inbound magnetic track to the holding fix 4. direction of turns 5. time along outbound leg or distance values, if necessary (up to FL140 1 minute, at or above FL150 1.5 minutes) 6. time at which the flight can be continued or a further clearance can be expected It is standard procedure to give general holding instructions unless one of the following points is met: - The pilot follows a holding procedure other than the published one - The pilot reports that he does not know the published holding procedure - The pilot must enter holding over a point for which no holding procedure is published The callsign and altitude can be highlighted in color in the tags when using Topsky to make it easier to see the aircraft in holding patterns. ### Holding capacity Incidentally, a holding pattern should not be assigned too high. If so many planes have to hold that the holding stack would be reach above FL200, you have to think about opening a second holding which has to have enough distance from the first one. This is often referred to as "enroute holding". If this is no longer possible in your own sector, the adjacent center sector must open a holding, as no more inbounds can be transferred from them to you. ### Terminate holdings Having the aircraft all circle in the holding pattern does of course not really present a challenge, but it becomes a real art as soon as the approach controller starts receiving airplanes again and you have to hand them over to them with a 10 NM spacing. Handing the whole holding stack over to APP so the controller can take airplanes out of the holding on their own only makes sense if the APP has at least the lowest 3-4 planes on their frequency. This is the only way they can get the airplanes into a sequence without wasting a lot of space. Ideally, CTR manages the exit from the holding pattern and only then hands the aircraft over to APP (coordination may be required for where CTR should clear the planes to). Letting each aircraft complete its holding and only then continue clearing them to APP definitely is a bad tactic. Doing this makes the 10 NM spacing you are aiming for an absolute coincidence, if it works at all. To improve this, you have to think ahead a lot: you have to instruct the next aircraft to leave the holding well in advance to stay on the outbound heading, on the "downwind" of the holding pattern, so to speak. Once it is shortly beyond the abeam point to the preceding traffic (which is already flying towards the holding fix, i.e. is virtually in the "final" of the holding), you simply turn it in behind it and you should get pretty much exactly 10 NM out of it. We aim for so much more spacing than when vectoring to the ILS because the aircraft are always significantly higher and therefore have a higher GS (although they are also flying at approx. 220 KIAS). At this point, the corresponding measure for the aircraft following the aircraft that has just turned back to the holding fix also has to have been initiated already. These holding patterns and their management really have a lot to do with advance planning. It is also very important to always quickly follow up with the cleared levels. As soon as a plane has left the holding, you clear the plane above it down to this now clear level. You can then have it report reaching this level, for example, so that you can immediately move the plane above it and do not forget to keep the cascade of airplanes being cleared down to the cleared levels below them moving. "Clearing out" a holding is therefore almost the same as feeding to the ILS. There is a downwind and a final, but you also always have to make sure that the airplanes are instructed to hold the outbound heading well in advance, because if you miss it once, you will lose quite a few miles. ### Holding Times Holdings should only be used for as long as necessary to avoid arrival running empty. APP and CTR must coordinate how long the aircraft need to be delayed. Often just one lap in the holding pattern (about 4 to 5 minutes) is enough to make sure that enough capacity is available again. It helps to consider or measure when the last aircraft is on final at APP. Taking into account the remaining distance for the inbounds, the reduction of the holding can be planned. ### Further links - **Skybrary:** [Holding Pattern](https://www.skybrary.aero/articles/holding-pattern "Skybrary - Holding Pattern") # Low Visibility Operations (LVO) - Arrival In case of low visibility conditions, the controller has to adapt the procedures at the airport to ensure a safe continuation of flight operations. However, controllers do not differentiate between CAT II and CAT III operations. The pilots must decide for themselves which approach they can fly based on the prevailing RVR and ceiling. Low visibility operations become active when the **runway visual range** (RVR) is **equal or** **less than 600** m and/or when the **ceiling** (BKN / OVC) is **below 200** ft or when there is no vertical visibility. The separation between two approaching aircraft or one approaching and one departing aircraft must be increased compared to standard operations so the ILS signals are not disturbed by approaching and departing traffic or by taxiing aircraft or vehicles on the ground. Approaches must be given the prevailing RVR together with the approach clearance. Which ILS category is used is up to the pilot and is therefore not mentioned in the clearance. > DLH123, turn left heading 220, cleared ILS runway 25L, RVR 300 metres. Depending on the volume of traffic, it may be necessary to increase the spacing between approaches to avoid missed approaches. # Center # Conflict detection #### Definitions **Conflict.** Predicted converging of aircraft in space and time which constitutes a violation of a given set of separation minima. **Conflict detection.** The discovery of a conflict as a result of a conflict search. **Conflict search.** Computation and comparison of the predicted flight paths of two or more aircraft for the purpose of determining conflicts. *Source: ICAO Doc 9426* #### Description Detecting conflicts between aicraft is an important part of the air traffic controller job and arguably the most complex one. Once a conflict is properly identified the resolution is relatively straightforward - the controller chooses an appropriate method (e.g. level change, [vectoring](https://www.skybrary.aero/index.php/Basic_Controller_Techniques:_Vectoring " Vectoring"), [speed control](https://www.skybrary.aero/index.php/Basic_Controller_Techniques:_Speed_Control " Speed Control"), etc.), implements the plan and monitors aircraft compliance. If the situation remains undetected, however, this may result in [loss of separation](https://www.skybrary.aero/index.php/Loss_of_Separation "Loss of Separation"), late (and more abrupt) manoeuvres, [STCA](https://www.skybrary.aero/index.php/Short_Term_Conflict_Alert_(STCA) "Short Term Conflict Alert (STCA)")/[TCAS](https://www.skybrary.aero/index.php/Airborne_Collision_Avoidance_System_(ACAS) "Airborne Collision Avoidance System (ACAS)") activation or worse. If all aircraft are assigned different levels, and are not expected to climb or descend, then there are no conflicts. Most commercial operations however take place in the [RVSM](https://www.skybrary.aero/index.php/Reduced_Vertical_Separation_Minima_(RVSM) "Reduced Vertical Separation Minima (RVSM)") layer which means that this situation is unlikely. Therefore, normally the first thing to be done in a surveillance environment, is a "**same level scan**", i.e. looking for aircraft that are maintaining the same level. This initial step identifies aircraft that need further examination. The second phase is to discard the pairs that are "obviously" non-conflicting, e.g. flying at the same speed to the same point with long distance between them, those whose paths do not cross, etc. After that, the minimum distance of the "suspicious" pairs is determined and, if necessary, a plan for solving the conflict is created. Climbing and descending flights present a special challenge as they require more checks to be done, e.g.: - Does the current level cause conflicts? - Will the final level for the sector cause a conflict (within the sector or at the exit point)? - Will any of the intermediate levels cause a conflict within the sector? - Will the aircraft be able to reach its planned level before the exit point? If not, will this cause a conflict in the next sector? These checks may become more complex if the aircraft climbs or descends through a high number of flight levels (e.g. climbing from FL 140 up to FL 360). This results in significant change in [groundspeed](https://www.skybrary.aero/index.php/Ground_Speed "Ground Speed") (due to [wind](https://www.skybrary.aero/index.php/Wind "Wind") and [IAS](https://www.skybrary.aero/index.php/Indicated_Airspeed_(IAS) "Indicated Airspeed (IAS)") variations) which hinders precise calculations. Factors that help controllers detect conflicts are: - system support (see section below) - discipline, i.e. performing structured scan of the aircraft that are, or will be under control and evaluation of the impact of each flight profile change - fixed-route environment. This usually means that there are fixed "hotspots" (normally where airways cross). An experienced controller can often detect a conflict by knowing that when there is an aircraft at point A then if the other one is at point B they will be in conflict at point C. - recurrent training for non-routine situations Factors that may cause a conflict to be missed include: - **Strong winds** (e.g. 50-100 kt or more). These may alter aircraft speeds in such a way that a [BOEING 737-300](https://www.skybrary.aero/index.php/B733 "B733") becomes faster than a [AIRBUS A-380-800](https://www.skybrary.aero/index.php/A388 "A388") in terms of groundspeed. Also, aircraft flying at different tracks will be affected differently. As a consequence, pairs that seem to be safely separated may be in conflict. - **[Free route environment](https://www.skybrary.aero/index.php/Free_Route_Airspace_(FRA) "Free Route Airspace (FRA)").** This means that the "standard" hotspots are no longer relevant and a situation may arise anywhere. While free route generally reduces the number of conflicts it makes them harder to identify. - **"Irregular" aircraft**, i.e. such that form a small fraction of the traffic flow and can be overlooked due to e.g. high [workload](https://www.skybrary.aero/index.php/Controller_Workload "Controller Workload") or [complacency](https://www.skybrary.aero/index.php/Complacency "Complacency"). Examples of these are **non-RVSM aircraft** in RVSM space, **slow-flying business jets**, **slow-flying aircraft** at lower levels (interfering with arriving and departing aircraft), non-routine situations (e.g. aicraft dumping fuel, military interception), etc. - [Deviation from procedures](https://www.skybrary.aero/index.php/Violation "Violation"), e.g. provision of ATS outside the area of responsibility, skipping "unnecessary" [coordinations](https://www.skybrary.aero/index.php/ATC_Unit_Coordination "ATC Unit Coordination"), etc. - **[Aircraft avoiding weather](https://www.skybrary.aero/index.php/Loss_of_Separation_During_Weather_Avoidance "Loss of Separation During Weather Avoidance")** are a special challenge, because their behaviour is less predictable and trajectory updates cause increased controller workload. If the controller does not update these, however, system support tools may be less useful. - **[Airspace boundaries](https://www.skybrary.aero/index.php/Conflict_Detection_with_Adjacent_Sectors "Conflict Detection with Adjacent Sectors")** are areas where conflicts are sometimes detected late. This can be caused e.g. by poor coordination, improper colour representation, etc. - **[Blind spots](https://www.skybrary.aero/index.php/Blind_Spots_%E2%80%93_Inefficient_conflict_detection_with_closest_aircraft "Blind Spots – Inefficient conflict detection with closest aircraft")** - a controller may examine the future path of an aircraft failing to notice the conflicting one which is just above (or below) - **Improper** [**handover/takeover**](https://www.skybrary.aero/index.php/The_Handover-Takeover_Process_(Operational_ATC_Positions) "The Handover-Takeover Process (Operational ATC Positions)"). The relieving controller normally expects all conflicts to be solved or at least detected and having a planned solution. If this is not the case, or if the controller being relieved fails to pass the information, it is possible that the new controller focuses on the medium and long-term situations and misses a near-term conflict. source: www.skybrary.aero # Conflict Solving This article describes the typical methods and controller actions used to solve conflict between aircraft in a surveillance (mostly en-route) environment. Only situations with two participating aircraft are considered. Although more complex scenarios (involving three or more aircraft) do exist, they happen rarely and in most cases can be considered as multiple two-aircraft cases that happen at the same time. In broader terms, a conflict is a situation where the separation at the [closest point of approach](https://www.skybrary.aero/index.php/Closest_Point_of_Approach_(CPA) "Closest Point of Approach (CPA)") will be less than the specified minimum and one of the following exists: - Two aircraft are flying at the same level. In this case, doing nothing will result in a [Loss of Separation](https://www.skybrary.aero/index.php/Loss_of_Separation "Loss of Separation"). There are two sub-scenarios to this: - Crossing conflict - the two aircraft's paths cross at some point and diverge afterwards. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/conflicts-1.png) - Converging conflict - the two aircraft's paths join at some point and remain the same afterwards, at least for a portion of the flight. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/conflicts-2.png) - At least one of the aircraft is climbing or descending to a level that will make it cross the other aircraft's level. In this case, doing nothing *may* lead to a loss of separation depending on the circumstances (e.g. vertical speed, distance between the aircraft, current vertical separation, etc.) - The two aircraft are vertically separated but at least one of them needs to be cleared to a level that would cross the other's level (e.g. due to reaching the top of descent). Here, doing nothing will *not* cause loss of separation. However, improper timing of the instruction to change level may lead to this. The second and the third situation usually happen near the transition between approach and area control. This is where departing aircraft reach their cruising level and arrivals start preparation for the final portion of the flight. The first one is more typical to the cruising part of the flight. Action to be taken by the controller in order to eliminate the risk of separation breach depends on a number of factors such as the type of conflict, the specific circumstances, the available aircraft performance, controller workload, etc. The most common methods for solving conflicts are: - [Level change](https://knowledgebase.vatsim-germany.org/books/enroute-study-guide/page/level-change). This solution is typically used for conflicting aircraft in level flight. In the crossing case, an opposite level may be used for a short time and then the aircraft will climb again to its cruising level. This is not an option in the converging scenario, meaning that the level change needs to be at least 2000 feet. Sometimes it is possible to use opposite levels for converging conflicts but this requires [coordination](https://knowledgebase.vatsim-germany.org/books/coordination "ATC Unit Coordination") with the downsteam sector or unit. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/conflicts-3.png)| Accomodation of climb requests | [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/rates-1.png) |
| Separation of departing and arriving traffic | [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/rates-2.png) |
| Descending arriving aircraft below the overflying traffic | [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/rates-3.png) |
| Vertical sequencing, i.e. establishing and maintaining vertical separation between two (or more) climbing or two (or more) descending aircraft | [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/rates-4.png) |
| Corrective action (e.g. when the unrestricted vertical speed is considered insufficient) | [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/rates-5.png) |
*Combined vertical speed is the sum of the vertical speeds of a climbing and a descending aircraft, e.g. if aircraft A is climbing at 1500 ft/min and aircraft B is descending at 2000 ft/min, then the combined vertical speed is 3500 ft/min.*
Source: [www.skybrary.aero](https://www.skybrary.aero) # Level Change While there are various reasons for a level change, this article focuses on the conflict solving aspect. #### Description Changing an aircraft's level is often the easiest way for a controller to solve a conflict, i.e. a situation where two (or more) aircraft are expected to be closer than the prescribed [separation minima](https://www.skybrary.aero/articles/separation-standards "Separation Standards"). Advantages: - Comparatively smaller intervention. The aircraft continues to fly using own navigation (as opposed to [vectoring](https://www.skybrary.aero/articles/basic-controller-techniques-vectoring "Basic Controller Techniques: Vectoring")) and follows the planned route (as opposed to proceeding direct to some distant waypoint). - Faster to achieve. Even when the aircraft is to climb or descend by 2000 ft, only 1000 are often enough to ensure separation with the conflicting aircraft (see section Opposite Levels for details). This means that the conflict is usually solved within less than a minute. - Easier to monitor on a [situation display](https://www.skybrary.aero/articles/situation-display "Situation Display"). Wind can influence both aircraft speed and flight direction. Additionally, speed vectors can change direction due to specifics of the surveillance system (especially the presence or absence of a tracker). On the other hand, all modern ATS systems provide an indication for climb or descend (an arrow next to the aircraft level). This makes it much easier for a controller to monitor aircraft compliance. - Less [controller workload](https://www.skybrary.aero/articles/controller-workload "Controller Workload"). Changing an aircraft's level normally requires one instruction and about a minute to achieve the required separation. By contrast, [speed control](https://www.skybrary.aero/articles/basic-controller-techniques-speed-control "Basic Controller Techniques: Speed Control") usually requires prolonged monitoring (the required separation "builds up" gradually). Vectoring requires more instructions - at least one for the heading change and one for the return to own navigation but more can be necessary depending on the circumstances. This will also require a longer period of monitoring. Disadvantages: - The main disadvantage of a level change is that aircraft normally fly at their optimal cruise levels. Therefore, any level change leads to reduced efficiency. This effect gets worse when increasing the difference between the desired and the cleared level. - The use of temporary level change (i.e. the aircraft climbs/descends to a safe level to solve a crossing conflict and then returns to its cruising level) requires two vertical movements (one climb and one descend) which is also sub-optimal in terms of efficiency. - There is an inherent risk of a blind spot, i.e. the controller may solve a medium term (e.g. 15 minutes ahead) conflict while at the same time create a new one with an aircraft just below or above the one being instructed to change level. - When vertically split sectors are used, the level change may require [coordination](https://www.skybrary.aero/articles/coordination-atc "Coordination in ATC") with an adjacent upper or lower sector which increases the workload for both controllers. #### Climb Vs. Descent After deciding to solve a conflict by a level change, the controller must choose between climb and descent. The former is generally preferred, as it leads to better flight efficiency. However, in some situations descent is the better (or the only) option, e.g.: - The aircraft is unable to climb due to weight. Note that weight reduces as fuel is burnt so a higher level may be acceptable later. In this case the controller should take into account that the climb rate could be less than usual. - The aircraft is approaching its top-of-descent. Instructing an aircraft to climb shortly before it would request descent is not very beneficial to flight efficiency and can increase controller workload (the higher the aircraft, the more potential for conflicts during the descent). - Turbulence is reported at the higher level. Vectoring, direct route or speed control are generally preferable in this situation. - The manoeuvre is to be performed quickly (e.g. due to a [conflict being detected](https://www.skybrary.aero/articles/conflict-detection "Conflict Detection") late). In this case, if a climb instruction is issued, it may be declined by the crew, thus losing precious time. If the controller is in doubt as of which option is preferable (and if both are available), the controller may first ask the pilot (time and workload permitting). The fact that the range of available speeds is reduced at higher levels should also be considered. If the climb is to be combined with a speed restriction, this should be coordinated with the crew beforehand. #### Opposite Levels In many situations a level change would require the aircraft to climb or descend by 2000 feet (so that the new level is appropriate to the direction of the flight). However, sometimes it is better to use an opposite level, i.e. one that is only 1000 feet above/below. This is often a good solution in case of crossing conflicts, i.e. where the paths of the two aircraft only intersect at one point and the level change is expected to be temporary. - The solution is better in terms of flight efficiency because the aircraft will fly as close as possible to the desired level and the need for vertical movement will be reduced - The opposite level may happen to be within the own sector, therefore no coordination with an adjacent upper or lower sector would be necessary. This reduces the workload of both controllers and is especially useful when there are multiple, vertically-split sectors. It should be noted, that a few risks exist with this solution: - If there is a flight on an opposite track, the normally expected 1000 ft separation would not exist - In case of radio communication failure, the aircraft may fly at an opposite level much longer than expected and the exact moment of returning to the previous level may not be easy to determine. The picture below show a situation where the use of opposite level is preferable. The level change will be required for a few minutes only and there is no opposite traffic. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/levelchange1.png) The picture below show a situation where the use of opposite level is not feasible because of opposite traffic. Therefore, a level change of 2000 ft is preferable. [](https://knowledgebase.vatsim-germany.org/uploads/images/gallery/2023-04/levelchange2.png) The use of opposite levels can sometimes be justified when the conflict is at the sector exit point. This solution, however, is subject to approval from the downstream controller. The feasibility of this option depends on the geometry of the conflict (are the aircraft diverging after the point of conflict) and on the traffic situation (are there aircraft that are flying at the same level on an opposite track). #### Priorities As a general rule, when two aircraft are at the same cruising level, the preceding aircraft would have priority, i.e. the succeeding aircraft will have to climb or descend. Other criteria may be specified in the manual of operations or other documents containing local procedures. In any case, the controller may deviate from these procedures based on the traffic situation. For example, if changing the level of the succeeding aircraft would create a new conflict (and thus, a new intervention would be necessary), the controller may opt to work with the preceding aircraft. Naturally, flights in distress, or those performing SAR operations, would have priority over other traffic. This includes obtaining (or maintaining) the desired level while a lower priority traffic (e.g. a commercial or general aviation flight) would have to change level. Other priorities may be specified in local procedures (e.g. flights with head of state on board). #### Vertical Speed Considerations Normally, vertical speed is not considered an issue in case of a level change solution to a conflict. This is because in most cases the instruction is issued well in advance (5-15 minutes before the potential separation breach) and the level change is 1000 or 2000 ft, which means that vertical separation will be achieved comfortably prior to losing the required horizontal spacing. Nevertheless, there are some situations where it might be necessary to ensure that the vertical speed will be sufficient. These include: - There is a reason to believe that the aircraft will not (be able to) climb fast, e.g. a heavy long-haul flight in the initial cruise stage, the aircraft type is known to climb slower than others, the new level is near the ceiling, etc. While 1000 ft/min means that 1000 ft separation will be achieved in one minute, if the rate drops to 200 ft/min, the required time will be 5 minutes. In the scenario where 2000 ft level change is necessary (e.g. converging traffic at the sector exit point and an opposite traffic 1000 ft above), a 200-300 ft/min climb rate will result in a 7-10 minute climb. - Sometimes, if a descent rate is not specified, the manoeuvre may start at rates in the range of 500 ft/min. In this case, a 2000 ft level change will require 4 minutes as opposed to only 1 or 2 if "normal" vertical speeds of 1000-2000 ft/min are used. In such situations the controller should either: - ensure the vertical speed will be sufficient (e.g. by specifying a desired rate of climb or descent), or - issued the instruction early enough, or - if the above are not possible, an use an alternative solution. Source: [www.skybrary.aero](https://www.skybrary.aero) # Runway Change Guide Runway changes might be tricky, especially during phases with a lot of traffic. This guide should help you to manage this situation. Example of a runway change at Frankfurt/Main EDDF from 07 ops to 25 ops. #### When is a runway change initiated? For this, a look at the **METAR** and the **TAF** is useful. Basically, runway 25 is preferred in case of a definite 25-wind (between 160 and 340 degrees) or variable wind (according to the regulations, up to a tailwind component of 5 knots, although it does not depend on one knot). In many cases, 07 is still used with constant weak 07 wind, e.g. 030/5, although the tailwind component on 25 is therefore less than 5 knots. The reason for this are smaller gusts, which are briefly larger than 5 knots, but are not displayed in the METAR). In case of doubt, a look at FR24 helps, which configuration is operated in real. However, in individual cases, there may be other reasons for a runway change in real (police helicopter mission, failure of navigation equipment, etc.). #### Who decides, when a runway change is initiated? The **tower supervisor/coordinator** decides to rotate, but Approach is involved in deciding exactly when to rotate (see below). #### How does the Runway Change work once the decision has been made? Tower calls Approach and informs about the upcoming runway change. In addition, the center controllers or, if available, a center supervisor should be informed so that other STARs can be cleared if necessary. Depending on the traffic situation, Approach then decides who will be the **last inbound for 07L and 07R** respectively. Apart from inbound rushes, it is usually quite simple: those who are already more or less across the field still get 07 in any case, while those who have just flown into the TMA are cleared for 25. Approach can either assign vectors or change the STAR for the pilot, depending on personal preference. In the inbound rush, however, Approach should try to find a suitable gap where there are not so many inbounds for a few minutes. If the wind is acceptable, the runway change can be postponed a bit if the inbound situation does not improve in the next few minutes. Nevertheless, after 20 minutes at the latest, a decision should be made as to who will be the last inbounds for 07L and 07R. In the optimum case, these are two aircraft that land at approximately the same time. **The call signs of these two aircraft are then passed on to the tower as well as an approximate landing time**. > "DLH123 last for 07L, DLH456 last for 07R, both landing in about 15 minutes". If the tower knows this, it must then be considered **for all outbounds whether they must be cleared for 25, or whether they can still depart from 07**. This consideration is primarily the task of the tower supervisor/coordinator. What must be avoided is that another outbound takes off from 07 even though the first planes are already on the 10-mile final approach of 25. Of course, the pilots should also be given a reason for the reclearance. > "We are changing runway direction, therefore you will be recleared, are you ready to copy?...". If, as in the example above, the last aircraft lands on 07 in 15 minutes, the tower can still allow take-offs from 07 for another 10 minutes. Based on the taxiing time, it is, therefore, necessary to estimate who will still get the 07. If in doubt, calculate conservatively and reclear too early rather than too late. Aircraft that are with apron control and are to be recleared must be sent back to Delivery since apron control is not allowed to issue route clearances. Delivery will contact Apron and ask them to send aircraft XY to Delivery for a reclearance. Outbounds, which are already at the tower frequency, may of course also be cleared by the tower. As soon as the aircraft are recleared, taxi instructions to holding point runway 25 are issued. Ideally, the aircraft will reach the holding point 25 when the last inbound 07 has just landed. However, a few minutes delay at the holding point is not a problem in such a situation.**Exceptions:** SULUS is cleared to 18 and KOMIB does not exist at 25, instead CINDY must be filed.
As soon as the last inbound for 07 is safely on the ground, the tower should inform Approach directly and, to be on the safe side, ask for a **release for the first 25 departure.** Approach, conversely, must time the inbounds so that the first 25-inbound is approximately on the **10-mile final approach** when the last 07-inbound is just touching down. In case of a missed approach at the last second, this gives enough room to turn away. If there is a lot of traffic, the downwind and final will automatically be very long. If necessary, aircraft will have to enter a holding for a short time, but this is usually not necessary, since the runway change should be timed as described above so that there is not so much traffic. Within the TMA, Approach can also get creative, e.g. with three-sixties, so that the downwind does not become too long. As with everything, it is important that the individual ATC stations **communicate and coordinate** so that everyone is fully aware of each other's traffic and plans. #### Summary - The decision is based on the METAR and TAF - The decision is made by the tower supervisor/coordinator, but approach is also involved in the decision - Approach decides the last arrivals for 07L and 07R - Tower can issue the last takeoff clearances for 07 until approximately 5 minutes before the last inbounds - The first inbound for 25 can be on a 10-mile final approach when the last 07-inbound is just touching down - The first 25 departure should be released by Approach # Emergencies - Controller Guide An **emergency** is, by definition, an emergency involving an aircraft in the air that poses a serious and immediate threat for the aircraft and/or its occupants. The handling of each emergency for the controller is highly individual, as no two situations are the same. This guide should therefore be seen as a basis / orientation. #### Relevance to Vatsim According to the [VATSIM Code of Conduct](https://vatsim.net/docs/policy/code-of-conduct), a pilot may only declare an emergency when they receive ATC service. The controller may request the pilot to terminate the emergency at any time and without giving reasons. The pilot must comply with this request immediately or disconnect from the network. Furthermore, no hijacking may be simulated and the transponder code 7500 may not be set.For you as an ATCO this means: **If you are not familiar with handling an emergency, rather refuse it. If you are currently too busy (e.g. due to a high traffic load), or are in doubt for any other reason, it is reasonable to refuse the emergency.** Neither the pilot nor you will benefit in any way if the emergency is handled unsafely, completely unrealistically or carelessly.
#### Types of emergencies On the **pilot's side**, there is a difference between the two well-known messages "Mayday" and "Pan Pan": - A "Mayday" is the notification of an emergency in which there is a serious or imminent danger and immediate assistance is required. - A "pan pan" is an emergency message in which a safety-relevant situation exists, but does not require immediate assistance. On the **controller side**, the term emergency is defined much more broadly. A distinction is often made between a local standby, a full emergency and an aircraft accident, although not all types of emergency fit into one of these categories. - A **local standby** is an aircraft that is known or suspected to have a malfunction which under normal circumstances does not prevent the aircraft from landing safely. Pilots often do not report a "pan pan" or a "mayday", but the flight is still considered an emergency by air traffic control. Certain measures are initiated which can only be simulated on Vatsim (e.g. calling out the fire department) Examples of a local standby are - Engine problems (e.g. strong vibrations, single engine failure) - Hydraulic problems (e.g. flaps cannot be extended) - Landing gear problems (e.g. nose wheel steering has failed) - Smoke / odor in the cockpit or cabin - Problems with cabin pressurization (e.g. broken windscreen) - Structural problems (e.g. after a bird strike) - A **full emergency** is an aircraft that is known or suspected to be in an emergency that results in a risk of an accident. The differentiation between local standby is sometimes blurred. Examples of a full emergency are - Aircraft fire / engine fire - Landing gear cannot be extended - An **Aircraft Accident** is an accident involving an aircraft that is at the airport or in the immediate vicinity of the airport. - Other emergencies that are not of a technical nature and therefore cannot be classified in any of the categories are, for example: - VFR with loss of orientation - VFR in IMC - Medical emergency in the aircraft - Radio failure #### Handling of an emergency As every emergency is different, there is no one-size-fits-all guide for handling emergencies. Nevertheless, there is a scheme that can help you as a controller to handle an emergency in a structured way in a stressful situation. This scheme is known as the **ASSIST scheme**, where each letter stands for a measure: - **Acknowledge**: The first thing to do is to recognize an emergency as such. The controller should therefore acknowledge "Mayday" and "Panpan" messages and also ensure that the nature of the emergency and any details have been understood correctly. - **Separate**: The surrounding airspace should be cleared to a greater or lesser extent depending on the emergency. This includes increasing the separation to the emergency aircraft by the center and approach controllers, as the cockpit crew is very busy or very stressed during an emergency and might implement ATC instructions late or incorrectly. On approach, the runway should be cleared as early as possible so that no "tight" maneuvers have to be performed with the aircraft concerned. If necessary, other approaches may be instructed to go around and VFR aircraft may be requested to leave the control zone. - **Support**: The pilot should be supported as much as possible. However, the pilot should not be distracted with unnecessary radio messages. Among others, the following support options are available: - Ask about general support / intentions - Suggest nearby / suitable airports - List / suggest approach types (depending on the weather, visual approaches may also be an option) - If there are several runways, suggest suitable runways (e.g. the longest / widest runway) - Clarify whether the pilot can leave the runway after landing and / or taxi normally - Simple instructions - radio messages should not contain more than one or two pieces of information - **Inform**: Other ATC stations affected by the emergency should be informed. For example, the center forwards the emergency to the approach, the approach to the tower and the tower to the ground. In this "game of telephone", particular care should be taken to pass on information correctly. - **Silence**: Depending on the situation and traffic load, radio silence can be imposed on the frequency. The phraseology here is in accordance with AIP GEN 3.4: - "All stations, stop transmitting, MAYDAY" - The following phraseology is used to cancel radio silence: "All stations, distress traffic ended" - **Time**: The pilot should never be stressed by the controller. They should be given sufficient time to solve their problem. Sometimes it can take several minutes to make a decision and work through the relevant checklists. # Identification Unlike tower controllers, radar controllers cannot look out of the window to provide air traffic services. They have to rely on data collected by so-called surveillance systems. Examples of these systems are primary surveillance radar (PSR) and secondary surveillance radar (SSR). #### Primary surveillance radar (PSR) When radar was invented, it only existed as a primary radar. A primary radar emits electromagnetic waves in all directions and displays a dot on the screen for each reflection detected. However, there is no way to tell which dot on the screen belongs to which aircraft - this is where identification comes into play.An aircraft is identified when we see its target on the radar screen and are sure which aircraft it belongs to.
But how can we know which target is which aircraft if it is not transmitting data? When using PSR, there are several so-called **identification methods** \[1\]: - **Position reports:** correlating a target with an aircraft reporting its position above or its distance and bearing from a significant point on the screen, and ensuring that the target's track matches the path/reported heading of the aircraft. - **Departing aircraft:** Assignment of a target to a departing aircraft within 1 NM of the end of the runway. - **"Turn" method:** Instruction to an aircraft to change course by 30 degrees or more and observation of this change. - **Transfer of identification:** The identification for an aircraft can be transferred to you by another controller who has identified it. #### Secondary surveillance radar (SSR) Modern surveillance systems use a transmitter-receiver combination that interrogates transponders on board the aircraft, which then transmit data back to the ground station. This is the fundamental difference to PSR systems, where the ground station receives passive signals (reflections). There are different interrogation modes that transmit different data \[2\]:| **Mode** | **Transported data** |
| A | 4-digit octal identification code, e.g. squawk |
| C | Aircraft's pressure altitude |
| S | Callsign, unique 24-bit address, selected altitude, speed over ground, indicated airspeed, etc. \[3\] |
This means that in the environment of Vatsim Germany (and with the standard ES packages) we can consider almost any aircraft as identified.
Before providing air traffic control services (any service provided directly using an ATS surveillance system, e.g. primary or secondary radar), the controller must identify the aircraft concerned and inform its pilot. **The information to the pilot about the identification may be omitted if the pilot was already identified by the previous sector.**
#### Reading and Deviation of Transponder Values This topic is less relevant on VATSIM than in real life. In reality, there are various rules that define when a flight level is considered "reached," "maintained," or "left." For VATSIM, however, it is generally sufficient to assume a tolerance of 200 feet. It is important to note that this should not be exploited to justify breaches of separation. In any case, pilots should be addressed about deviations (and, for example, asked to correct their altimeter settings). \[1\] ICAO Doc 4444, Procedures for air navigation services - Air traffic management, Sixteenth edition, 2016 \[2\] [Aviation transponder interrogation modes, Wikipedia](https://en.wikipedia.org/wiki/Aviation_transponder_interrogation_modes) \[3\] [Skybrary Mode S](https://www.skybrary.aero/articles/mode-s)