Abstract: A thrust demand signal is provided to a processor of a gas turbine engine and is modified, according to growth time constants of a rotor and/or a casing of the engine, in order to control the rotational speed or the rate of change of rotational speed of the engine so as to prevent contact between the rotor and the casing.

Abstract: A method of controlling an aircraft gas turbine engine cooling system. The cooling system includes a heat exchanger having a first fluid path through which fan air flows, and a second fluid path through which relatively hot compressor air flows. The cooling system includes a valve configurable between an open position corresponding to a first operating mode, where fan air flows through the first path cooling the compressor air in the second path to a lower temperature, and a closed position corresponding to a second operating mode, where fan air may flow through the first path at a reduced rate, thus the compressor air in the second path could be cooled to a lesser extent. The valve is operated in first mode when the aircraft is in a descent mode, or when turbine entry temperature is above a predetermined amount. Otherwise, the valve is operated in second mode.

Abstract: A method of constructing a piecewise linear engine performance model, comprises the steps of: (a) providing a non-linear engine performance model which iteratively calculates engine performance variables y from a plurality of sub-models, each sub-model representing the performance of a component of the engine; (b) defining a plurality of engine power conditions, each engine power condition being defined by one or more engine state variables x; (c) for each of the engine power conditions, using the non-linear engine performance model to determine partial derivatives ?y of the engine performance variables y with respect to engine control variables u and with respect to the engine state variables x, the values of the partial derivatives ?y being determined so that, on integrating the partial derivatives ?y, the error between steady state values for the engine performance variables y calculated by the non-linear engine performance model and steady state values for the engine performance variables y calculated