Towards the end of the flight the Central Warning System indicated an oil pressure loss on the No 2 engine. The engine was shut down and an uneventful single engine landing was carried out. It was found that a cap locating the propeller overspeed governor test solenoid had detached, allowing most of the oil from the No 2 engine lubrication system to be lost. Investigation of the component revealed that the four cap securing bolts had failed, predominantly in fatigue. Extensive investigation failed to identify conclusively the root cause of the bolt fatigue damage. Although three similar in-service failures of these bolts have occurred on other aircraft types utilising this design of governor, no others have been recorded on DHC 8-400 types and all those that have occurred have been on units of an earlier modification state.
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