# Wake turbulence separation Wake turbulence: yet another abstract new term. [This video](https://www.youtube.com/watch?v=5BipbyQreiM&t=1s) explains what wake vortices are and how they arise. And what do air traffic controllers have to do with it? We have to make sure that accidents like the one shown in the video in New York don't happen again. There are minimum separation values for this depending on the maximum take-off mass of the aircraft and we as controllers need to make sure these separation distances are maintained at all times. #### When must wake turbulence separation be applied? Wake turbulence separation is used in areas where wake turbulence is expected. Between aircraft with **obligatory radar separation** (see [radar separation](https://knowledgebase.vatsim-germany.org/books/separation/page/radar-separation "Radar separation")), if: - an aircraft is directly behind a preceding aircraft at the same altitude or less than 1000ft below - an aircraft crosses directly behind another aircraft - at its 6 o'clock position - at the same altitude or less than 1000ft below Between aircraft in the **approach or departure phase** of flight when: - an aircraft is directly behind a preceding aircraft at the same altitude or less than 1000ft below it - an aircraft crosses directly behind another aircraft - at its 6 o'clock position - at the same altitude or less than 1000ft below it - both aircraft are using the same runway or parallel runways less than 760m apart - the aircraft use crossing or parallel runways (distance of 760m or more) and one aircraft flies through the flight path of the preceding aircraft at the same altitude or less than 1000ft below it
Wake turbulence separation does not apply to:
- approaching VFR flights - approaching IFR flights that are performing a visual approach, have reported the preceding aircraft in sight and have been instructed to follow it and maintain their own separation In these cases, a **wake turbulence warning (CAUTION WAKE TURBULENCE)** must be issued. ##### Departure phase A VFR flight is in the departure phase from take-off until - reaching 1000ft above aerodrome level or - reaching level flight or - entering (right) downwind ##### Approach phase A VFR flight is in the approach phase when it is at or below 1000ft above aerodrome level and - has entered the traffic pattern or part of it or - has begun the final descent within a control zone until landing.A **touch-and-go** is considered an approaching aircraft until touchdown, from then on it is handled as a departing aircraft. A **low-approach** is considered to be an approaching aircraft until it crosses the runway threshold, after which it is considered to be a departing aircraft.
#### Wake turbulence categories For this purpose, aircraft are divided into four wake turbulence categories (WTC) according to their maximum take-off mass (MTOM).WTC | MTOM |
Light (L) | MTOM ≤ 7t |
Medium (M) | 7t < MTOM < 136t |
Heavy (H) | MTOM ≥ 136t |
Super (J) | A388; A225 |
The Boeing 757 counts as heavy in Germany despite an MTOM of less than 136 tons.
Aircraft in the “Super” category are treated as “Heavy” above flight level 100.
#### Minimum separation values Wake turbulence separation can either be distance-based or time-based. As a standard procedure, distance-based wake turbulence separation is used. However, there are also constellations in which this is not possible and in these cases time-based wake turbulence separation is used. ##### Distance-based**Preceeding** | **Suceeding** | **Separation value** |
M | L | 5 NM |
H | L | 6 NM |
M | 5 NM | |
H | 4 NM | |
J | L | 8 NM |
M | 7 NM | |
H | 6 NM |
**Preceeding** | **Suceeding** | **Separation value** | **Separation value (intersection)** |
M | L | 2 min | 3 min |
H | L | 2 min | 3 min |
M | 2 min | 3 min | |
J | L | 3 min | 4 min |
M | 3 min | 4 min | |
H | 2 min | 3 min |
**Preceeding** | **Suceeding** | **Separation value** |
M | L | 3min |
H | L | 3min |
M | 2min | |
J | L | 4min |
M | 3min | |
H | 2min |