The US Federal Aviation Administration plans issue an airworthiness directive calling on Sikorsky S-92 operators to repetitively inspect the helicopter's main gearbox mounting feet for cracks, defects that could lead to gearbox detachment and loss of control of the helicopter.

The FAA mandate will follow an emergency airworthiness directive issued by the European Aviation Safety Agency on 23 October after reports that cracks had been found in the feet, pads and foot ribs on main gearboxes during inspections. "In one case, the mounting foot was completely severed from the gearbox," says EASA. "Other cases include cracks at the fore and aft mounting bolt location on the right-hand side of the mounting foot."

Regulators began scrutinising S-92 main gearboxes after the fatal crash of a Cougar Helicopters S-92 off the coast of Newfoundland in March. Early findings from that investigation, which is ongoing, revealed that mounting studs for the main gearbox oil filter had potentially broken off in flight, leading to the loss of all lubricant. Authorities later issued ADs to replace the original factory titanium mounting studs with steel versions.

Sikorsky S-92
 © Sikorsky

The FAA began developing the latest AD in September, it says, but was unable to complete it as it waited for Sikorsky to submit a failure analysis for the main gearbox mounting feet and other information. The FAA says the cracking phenomenon, while seen in the North Sea, has not been experienced by operators in the USA and Gulf of Mexico.

The FAA says EASA notified officials on 23 October it was considering issuing an AD and wanted FAA comments. "EASA issued their AD that same day, prior to us making any comments," says the FAA, adding: "We plan to follow up shortly with our own AD."

Source: Flight International