A departure starts from the beginning of the runway. At this point the aircraft’s position tolerance is very small. Once the aircraft is airborne the tracking tolerance increases by +15° until the aircraft is at a position or altitude to receive navigational guidance. This straight-ahead portion of the flight is relative easy to construct but when a turn is required the fix area and turn parameters, discussed previously, come into effect.

The real difficulty with designing a departure procedure occurs when the third dimension (altitude) is taken into account.