Patent ID: 8838299

Claim:
A method of controlling automatic following of a lateral profile and automatic following of a vertical profile of an automatic guidance system of an aircraft flying on a reference trajectory, comprising the steps of: disengaging automatic following of the lateral profile, while automatic following of the vertical profile remains engaged; estimating a projected lateral deviation distance of the aircraft from the lateral profile corresponding to the reference; and automatically disengaging automatic following of the vertical profile if the projected lateral deviation distance plus an associated lateral position error is greater than a predetermined threshold; wherein estimating the projected lateral deviation distance comprises: when the aircraft is not in a turn, estimating the projected lateral deviation distance by a function comprising propagating a current position of the aircraft by a predetermined time period along a current heading of the aircraft; when the aircraft is in a turn that causes the aircraft to converge towards the reference trajectory, estimating the projected lateral deviation distance based on a maximum lateral deviation of the aircraft from the reference trajectory while in the turn; and when the aircraft is in a turn that causes the aircraft to diverge from the reference trajectory, estimating the-projected lateral deviation distance by a function comprising propagation of the turn over the predetermined time period from the current position of the aircraft.