Engineers have discovered a hairline crack in the gearbox of a Canadian-based Sikorsky S-92 helicopter, the latest chapter in an ongoing mechanical saga that has cast an investigative spotlight on the high-tech machine.
The crack was found Monday during a routine inspection of a S-92 operated by Cougar Helicopters out of Halifax. Last March, a Cougar S-92 crashed off the Newfoundland coast, killing all but one of the 18 people aboard.
The gearbox crack found Monday is the latest in a series of faults with the S-92 gearbox, which has been the subject of emergency airworthiness orders by international aviation regulators.
Last month, the European Aviation Safety Agency issued an emergency airworthiness directive (AD) after gearbox cracks were found in three S-92's operated in the North Sea. Just days ago, the US-based Federal Aviation Administration issued its own AD, ordering operators to inspect the S-92's main gearbox and its mounting points.
The S-92's main gearbox has been the subject of intense scrutiny since the Newfoundland crash. In March, a Sikorsky S-92 operated by Cougar Helicopters went down in the Atlantic after the pilots issued a mayday call. Investigators discovered broken studs on the helicopter's main gearbox oil filter, which would allow the oil to leak out. A Globe and Mail investigation revealed a series of gearbox oil loss incidents with the S-92 design.
After probing the Newfoundland crash and other S-92 incidents, aviation authorities ordered key changes, including the replacement of the titanium gearbox filter studs with steel ones. Several oil-loss incidents, including the Newfoundland crash, have sparked a continuing dispute within the aviation community about the S-92's "run-dry" capabilities.
The S-92 was certified to an advanced safety standard known as FAR Part 29, which calls for a helicopter to be able to run for at least half an hour with no oil in its main gearbox. A Globe and Mail investigation revealed that the S-92 could not achieve that, but was certified after Sikorsky showed that the chance of losing gearbox lubrication was "extremely remote."
But with just over 100 helicopters sold, the S-92's record has fallen far short of the required standard, which defines "extremely remote" as approximately one failure in 10 million flying hours. The S-92's run-dry capabilities have also sparked sharp debate about a multibillion-dollar contract with the Canadian military. An S-92 variant called the Cyclone MH-92 was chosen as a replacement for Canada's aging Sea King helicopter fleet. Defence Minister Peter MacKay says the government will not accept the Cyclone unless it meets the run-dry specifications set out in the contract.
Sikorsky spokesman Paul Jackson says the Cyclone's gearbox will be substantially different than the civilian version, but would not specify details.
The cracks discovered in the Halifax-based Cougar S-92 yesterday were in mounting feet of the main gearbox, the same location as those found in the North Sea machines last month.
"During a scheduled inspection of the main gearbox feet of a S-92A Cougar engineers identified a single hairline crack in the right-hand mounting foot of the main gearbox," Cougar Helicopters said in a news release.
A helicopter's main gearbox is considered a critical component. Although pilots are trained to deal with engine failures, the seizure of a main gearbox is a catastrophic event, because it stops the main rotor blades, leaving no recovery options.
An inquiry into last March's fatal crash has begun in Newfoundland. In June, just two months after a Globe and Mail investigation that revealed the S-92's little understood gearbox certification issues, Sikorsky and its subsidiary were sued by the sole survivor of the Newfoundland crash, and the families of those who died. Just five weeks later, the plaintiffs withdrew their suit after announcing that they would " engage in alternative dispute resolution" with the company.