The investigation has identified a 360° circumferential crack in the bevel gear vertical shaft in the main gearbox, in the vicinity of a manufacturing weld, causing disengagement of the drive to both mechanical oil pumps
Driving both oil pumps from the same shaft - the main and stand-by - evidently enables a single failure to cause complete loss of oil pressure.
Am I being old fashioned by suggesting that any stand-by system should be totally seperate from the main system, and any failure (short of a catastrophic xmsn disintegration) that causes the main to fail shouldn't affect the stand-by?