Verification of level information

As you know a mode C transponder gives information about the pressure altitude of an aircraft. To use this level indication for vertical separation a controller is obliged to verify this level information as soon as possible after initial contact. To do so you simply compare the reported level of the pilot to the one indicated on your radar screen. Taking into account real life regulations, a discrepancy of 200ft is allowed to exist. Within VATSIM’s simulated environment, a higher offset can be accepted. If the reported level differs significantly from the one indicated on your radar, the controller shall instruct the pilot:

DLH123A, CHECK ALTIMETER SETTING AND CONFIRM LEVEL / (level)

If the problem persists after the correct pressure setting is confirmed, the pilot shall be instructed to stop the altitude data transmission:

DLH123A, STOP SQUAWK CHARLIE WRONG INDICATION

The next sector has to be informed and level reports shall be used to ensure vertical separation. 

Often wrongly considered as a part of the identification process, a pilot’s level report is completely independent from the procedures shown in the previous chapter.