British investigators are focusing on a fractured bevel-gear, vertical drive shaft as a contributing factor in the North Sea ditching of a Bond Offshore Eurocopter EC225LP Super Puma (G-REDW) 20 nm east of Aberdeen, Scotland, on May 10. The UK’s Air Accidents Investigation Branch (AAIB) issued a bulletin late last week on its preliminary findings.
Investigators found the shaft failed after 167 flight hours, causing a failure of primary lubrication to the helicopter’s main gearbox (MGB). The crew elected to ditch when an annunciator light warned that the back-up MGB lubrication system had also failed. Emergency pop-out floats were deployed and the crew and 12 passengers were rescued. Two passengers sustained minor injuries.
Investigators have yet to determine conclusively why the “MGB EMLUB” warning light illuminated; however, a valve in the system that should have been closed was found to be slightly open. Following the ditching, 18 vertical drive shafts from the same manufacturing lot were examined and “a number were found to be outside the design tolerance,” according to the AAIB.