Aircraft cruise speed control

1. A method for controlling a flight speed of an engine propelled aircraft, the method comprising:

in a computerized control system:

receiving a cruise control request signal for engaging a cruise control mode of operation of the engine;

receiving a flight stability condition signal indicative of whether a flight stability condition is met, wherein the flight stability condition is met when the aircraft is in a stable flight path and in one of flight level transition and final approach;

activating the cruise control mode upon receipt of the cruise control request signal and when the flight stability condition is met;

receiving a flight speed signal indicative of the flight speed; and

in the cruise control mode, automatically adjusting only a thrust setting of the engine within a given range according to the flight speed signal to maintain the flight stability condition.

2. The method as claimed in claim 1 , wherein the step of adjusting the thrust setting includes the step of adjusting an engine speed (N 1 ) signal within an engine control system of the aircraft.

3. The method as claimed in claim 2 , further comprising deactivating the cruise control mode when flight stability condition is no longer met, and wherein the step of deactivating includes smoothly fading out any N 1 signal adjustment to zero.

4. The method as claimed in claim 3 , wherein the adjustment is faded out linearly over 2 seconds if the disengagement occurred due to a failure in the function or a pilot disengage request received.

5. The method as claimed in claim 3 , wherein thrust lever angle is moving when the at least one stability criterion is no longer met, and wherein the step of deactivating includes keeping any N 1 adjustment substantially constant while the thrust lever angle is moving and then fading out any N 1 signal adjustment to zero once thrust lever angle movement substantially ceases.

6. The method as claimed in claim 1 , wherein the aircraft has a plurality of prime mover engines, the method further comprising entering an OEI mode when one of the engines is inoperative, wherein in said mode said thrust setting given range is increased for a remainder of the plurality of engine.

7. The method as claimed in claim 6 , further comprising receiving an OEI signal indicative of said engine being inoperative and wherein the OEI mode is entered automatically upon receipt of the OEI signal.

8. A flight speed control system for controlling a flight speed of an engine propelled aircraft, the system comprising:

a first input for receiving a cruise control request signal for engaging a cruise control mode of operation of the engine;

a second input for receiving a flight stability condition signal indicative of whether a flight stability condition is met, wherein the flight stability condition is met when the aircraft is in a stable flight path and in one of flight level transition and final approach;

a logic circuit for activating a cruise control mode upon receipt of the cruise control request signal and when the flight stability condition is met;

a third input for receiving a flight speed signal indicative of the flight speed; and

an engine controller in the cruise control mode configured for adjusting only a thrust setting of the engine within a given range according to the flight speed signal to maintain the flight stability condition while in the cruise control mode.

9. The flight speed control system as claimed in claim 8 , wherein the logic circuit includes an apparatus for adjusting an engine speed (N 1 ) signal in the engine controller.

10. The flight speed control system as claimed in claim 8 , wherein the aircraft has a plurality of prime mover engines, the system further comprising a fourth input for receiving a OEI-engine inoperative signal, and wherein the upon receipt of such signal the engine controller is configured to increase said thrust setting given range for a remainder of the plurality of engines.