In another safety issue affecting the Sikorsky S-92 helicopter’s main gearbox, on July 18 the FAA released an airworthiness directive (AD) that calls for inspection for cracks. The AD was prompted by the discovery of a crack in the gearbox housing of one S-92, “in the cored passage area adjacent to the scissor bracket mount,” allowing oil to leak. The result could be a loss of oil and subsequent failure of the gearbox, the FAA said.
Operators can choose between repetitive visual inspections and a one-time eddy current inspection. Repetitive visual inspections should be made within 10 hours of time in service or 15 days, whichever occurs earlier, and subsequently before the first flight or each day. Time in service between two inspections should not exceed 10 hours.
If a crack is found, the gearbox must be replaced.
The FAA estimates the AD will affect 16 helicopters on the U.S. registry. Gearbox failure after a loss of oil was determined to be the cause of the 2009 fatal crash of a Cougar-operated S-92 off Newfoundland.