Method for predicting the operational reliability of an aircraft system

A prediction method of the reliability of an aircraft system (S) onboard an aircraft and constituted by a plurality of elements, the operation of said aircraft comprising a sequence of cycles, each cycle comprising a flight phase and a ground station phase, characterised in that it comprises:

• an initialization step (510) of the probabilities of good operation or faultiness of each element (Pr{xD1}, Pr{ xD1}) at the beginning of the said operation;
• and an iterative loop, each iteration corresponding to an operation cycle and including:
• a first estimation step (520), for each element, of the upper (UB(TLT|xFT∩xDT)) and lower (LB(TLT|xFT∩xDT)) bounds of the conditional breakdown probability of the system if the said element breaks down during said cycle, the estimation being done from the minimal cuts of the default tree, the minimal paths of the reliability diagram of said system and the upper and lower bounds of probability of good operation (UB(xDT);
• LB(xDT)) or faultiness (UB( xDT), LB( xDT)) of the different elements at the beginning of said cycle;
• a second estimation step (530) of the upper (UB(TLT)) and lower (LB(TLT)) bounds of the probabilities of the breakdown of said system from the upper and lower bounds estimated at the first step for the said different elements of the system and the respective probabilities of the different elements of the system of breaking down during a cycle (Pr{xFT|xDT});
• a third estimation step (540), for each element of said system, of the upper (UB(TLT∩ xDT)) and lower (LB(TLT∩ xDT)) bounds of the conditional breakdown probability of the system during said cycle if the said element were faulty at the beginning of the cycle, the estimation being done from the minimal cuts of the default tree and the minimal paths of the reliability diagram of said system;
• a fourth estimation step (550) of the upper and lower bounds of probability of good operation (UB(xDT+1);
• LB(xDT+1)) or faultiness (UB( xDT+1), LB( xDT+1)) of the different elements of the system at the beginning of the following cycle, from the upper and lower bounds estimated by the first step, as well as the upper and lower bounds estimated by the third step.