Patent ID: 7725224

Claim:
A method of detecting at least one oscillatory failure in at least one position servocontrol subsystem of at least one control surface of an aircraft, said servocontrol subsystem being part of an electrical flight control system of the aircraft, said method comprising: setting a position of said control surface relative to the aircraft surface, in accordance with at least one received actuation instruction, wherein said control surface is mobile; measuring the actual position of said control surface; and operating a computer to (i) generate a control surface control instruction, (ii) receive said measured actual position, and (iii) deduce from said measured actual position an actuation instruction which is transmitted to said actuator, wherein, automatically and repetitively, the following successive series of steps is carried out: a) estimating a position corresponding to a reference position of said control surface in the absence of failure using said control surface control instruction which feeds a model of said actuator; b) computing a difference between said position estimated in step a) and said actual position to form a residual value; and c) comparing the residual value to at least one predetermined threshold value, counting successive and alternating overshoots of said predetermined threshold value by said residual value, and, determining that an oscillatory failure exists when the number resulting from said count becomes greater than a predetermined number, representing a sinusoidal periodic signal, the frequency, amplitude and phase of which follow a uniform law.