Turbine clearance control system

A turbine engine active clearance control systein is activated based on a flight phase of an aircraft using the engine and adjusts a turbine clearance based on a preselected value. The clearance control may be enabled using a switch operated by an operator or remotely using signals from another aircraft or an air traffic controller. A stable flight phase can be determined by comparing the rate of change of a measured engine parameter, such as core speed, fuel flow and temperature, with a threshold. An operator such as a pilot may be notified of clearance control activation by a display (fig 4,204) or aurally. The system may determine the turbine clearance and adjust the gap in response. The clearance control system may be de-activated a preset time before the end of a stable flight phase.