Method for detecting malfunctioning of a fuel return valve in an aircraft

A method for monitoring a fuel return valve (FRV), the FRV controlling a flow of fuel, used to cool an oil feeding a propulsion engine of an aircraft and an oil of an integrated drive generator (IDG) from a fuel distribution system to the propulsion engine to a recirculation system returning hot fuel to a fuel tank of the aircraft, an aperture of the FRV configured to increase a flow of fuel circulating in the fuel distribution system, the fuel being colder fuel originating from said fuel tank of the aircraft, a first oil temperature sensor supplying oil temperature measurements at an outlet port of the IDG, a second oil temperature sensor supplying measurements of a temperature of oil feeding the propulsion engine, the method being implemented by an FRV operation monitoring system comprising electronic circuitry, the method comprising the following steps:

• receiving measurements from the first oil temperature sensor of a first oil temperature and from the second oil temperature sensor of a second oil temperature;
• identifying, over a total number of flights, a sliding window of Z flights, the Z flights being a consecutive subset of the total number of flights, exceeding a duration D for monitoring the first oil temperature and the second oil temperature, the sliding window updated with each flight of the aircraft up to the total number of flights;
• determining, for each flight of the aircraft, a maximum oil temperature at the outlet port of the IDG according to the measurements of said first oil temperature sensor, or a maximum oil temperature of the propulsion engine according to the measurements of said second oil temperature sensor, or according to both;
• assessing a trend of the maximum oil temperature at the outlet port of the IDG, or the maximum oil temperature of the propulsion engine, or both over the Z flights;
• generating an alarm flagging a malfunction experienced by the FRV, the malfunction leading to an undesirable closure of the FRV and thereby leading to an undesirable temperature rise of the oil used to cool the IDG, when the trend of the maximum oil temperature shows that a predetermined oil temperature threshold (T) has been exceeded during Y flights of the sliding window of Z flights, with Y and Z predetermined values such that Y<Z.