The European Aviation Safety Agency (EASA) issued an Emergency Airworthiness Directive (AD) requiring a hydraulic power – high pressure manifold check valve inspection on Airbus A330 and A340 models.
An A330 operator experienced a low level of the Yellow hydraulic circuit due to a loose of check valve part number (P/N) CAR401. During the inspection on the other two hydraulic systems, the other three CAR401 check valves were also found to be loose with their lock wire broken in two instances.
A340 aeroplanes are also equipped with the same high pressure manifold check valves.
Investigations are on-going to determine the root cause of this event.
Additional cases of CAR401 check valve loosening have been experienced in service on aeroplanes having accumulated more than 1 000 flight cycles (FC). The check valve fitted on the Yellow hydraulic system is more affected, probably due to additional system cycles induced by cargo door operation.
The loss of torque due to pressure cycles could contribute to check valve loosening, resulting in a leak and finally the loss of the associated hydraulic system and, in the worst case, of the three hydraulic systems of the aeroplane.
This AD requires to perform the following inspection programme to detect any check valve loosening and, if necessary, apply the associated corrective actions:
1st Step: on yellow and blue hydraulic circuits: lock wire inspection, inspection for traces of seepage or black deposit, check valve torque and red marking application.
2nd Step: on green hydraulic circuit: same inspections as required in 1st Step and on yellow and blue hydraulic circuits: inspection of check valves for condition.
Finally: on green, yellow and blue hydraulic circuits: repetitive inspection of check valves for condition. (EASA)