Loss of lubrication to the main gearbox (MGB) has been responsible for several crashes, ditchings and precautionary landings in large transport category helicopters in recent years. These accidents set off broad debate as to exactly what is required of main gearboxes under Part 29 certification of the U.S.
The EASA has issued a new emergency AD on the Eurocopter EC225, requiring crews to land or ditch immediately if the main gearbox’s back-up lubrication system activates. “Investigations on the [emergency lubrication] system have revealed an area of the flight envelope in which the [system’s] performance is different from that assumed during certification,” the EASA said. The system was designed to allow for 30 minutes of flight after loss of oil lubrication.
The UK Air Accidents Investigation Branch (AAIB) has explained why the emergency lubrication system sent a “failure” warning–while working nominally–to the crews of the two Eurocopter EC225s that ditched in the North Sea last year.
The FAA is moving to redefine what “extremely remote” means when it comes to Part 29 certification provisions regarding loss of helicopter gearbox lubrication. The S-92 originally gained certification after Sikorsky convinced the FAA that complete loss of lubrication was extremely remote. Failure of the main rotor gearbox lubrication system is blamed for the fatal ditching of a Cougar Helicopters S-92A off Newfoundland in March 2009.