Patent ID: 8340843

Claim:
Method for determining the speed of an aircraft that is subject to a time constraint (RTA) expressed in the form of a fixed date at a determined point, the aircraft exhibiting a limit speed profile (V.sub.limit), the aircraft comprising a flight management system calculating a predicted time of arrival (ETA) of the aircraft at the point on following a speed setpoint expressed in the form of a pair of constant speeds (CAS,MACH), the flight management system calculating, furthermore, a first arrival time (ETA.sub. 1 ) of the aircraft at the setpoint on following a pair of constant limit speeds (CAS.sub.limit,MACH.sub.limit), the aircraft following the first speed of the pair (CAS.sub.limit) when the aircraft flies at an altitude below a predefined altitude (Alt.sub.Max), the method comprising: a. calculating a second arrival time (ETAenv.sub. 2 ) according to the limit speed profile (V.sub.limit), the limit speed profile comprising a maximum speed and a minimum speed of the aircraft; b. calculating a deviation (.DELTA..sub.ETA) to the time constraint: .DELTA..sub.ETA=|ETA−RTA|, the deviation to the time constraint .DELTA..sub.ETA being equal to the absolute value of the difference between the predicted arrival time ETA of the aircraft at the point on following a speed setpoint and the time constraint RTA; c. calculating a first speed profile CAS(alt.sub. 1 ) dependent on an altitude on the basis of the limit speed profile (V.sub.limit), with alt.sub. 1 being an altitude between 0 and the predefined altitude (Alt.sub.Max); d. calculating a second speed profile MACH(alt.sub. 2 ) dependent on an altitude, on the basis of the limit speed profile (V.sub.limit), with alt.sub. 2 being an altitude between the predefined altitude (Alt.sub.Max) and a cruising altitude e. updating the predicted arrival time (ETA) by taking into account the calculated first and second speed profiles CAS(alt.sub. 1 ) and MACH(alt.sub. 2 ); f. calculating the deviation (.DELTA..sub.ETA) of the time constraint: .DELTA..sub.ETA=|ETA−RTA|, the deviation to the time constraint .DELTA.sub.ETA being equal to the absolute value of the difference between the predicted arrival time ETA of the aircraft at the setpoint on following a speed setpoint and the time constraint RTA; g. returning to the step of calculating the first speed profile CAS(alt.sub. 1 ) if the deviation to the arrival time (.DELTA..sub.ETA) is nonzero, otherwise applying the calculated speed profiles to the aircraft.