A system for controlling a multi-engine aircraft, the aircraft comprising at least a first engine (10 1) and a second engine (10 2), at least a selected one (10 1) of which is operatively connected to an accessory drive train (110 1) for driving an aircraft accessory, a gearbox operatively connecting the first and second engines to a prime mover propulsor (102,104) of the aircraft, and an actuator operatively associated with the at least one selected engine (10 1) and moveable between a first position, in which the at least one selected engine (10 1) drivingly engages the gearbox for driving the propulsor (102,104), and a second position, in which the at least one selected engine (10 1) disengages from the gearbox, characterised in that the system comprises: a memory having stored therein a predetermined speed threshold for engaging/disengaging a said at least one selected engine (10 1); and a processing unit coupled to the memory and configured to: receive a position signal indicative of a present position of a said actuator, the present position being one of a said first position and a said second position; receive a status signal indicative of a present governing state and a present speed of each of said at least first and second engines (10 1, 10 2); receive a request signal indicative of a request for movement of the actuator from the present position to the other one of the first position and the second position; compare the present speed of the at least one selected engine (10 1) to the threshold; if the present speed differs from the threshold, output a first control signal for causing the present speed of the at least one selected engine (10 1) to be adjusted upwards or downwards towards the threshold; and output a second control signal indicating that the requested movement of the actuator is permitted. a memory having stored therein a predetermined speed threshold for engaging/disengaging a said at least one selected engine (10 1); and a processing unit coupled to the memory and configured to: receive a position signal indicative of a present position of a said actuator, the present position being one of a said first position and a said second position; receive a status signal indicative of a present governing state and a present speed of each of said at least first and second engines (10 1, 10 2); receive a request signal indicative of a request for movement of the actuator from the present position to the other one of the first position and the second position; compare the present speed of the at least one selected engine (10 1) to the threshold; if the present speed differs from the threshold, output a first control signal for causing the present speed of the at least one selected engine (10 1) to be adjusted upwards or downwards towards the threshold; and output a second control signal indicating that the requested movement of the actuator is permitted. receive a position signal indicative of a present position of a said actuator, the present position being one of a said first position and a said second position; receive a status signal indicative of a present governing state and a present speed of each of said at least first and second engines (10 1, 10 2); receive a request signal indicative of a request for movement of the actuator from the present position to the other one of the first position and the second position; compare the present speed of the at least one selected engine (10 1) to the threshold; if the present speed differs from the threshold, output a first control signal for causing the present speed of the at least one selected engine (10 1) to be adjusted upwards or downwards towards the threshold; and output a second control signal indicating that the requested movement of the actuator is permitted.