Newly released documents show that the model of helicopter involved in a fatal crash off Newfoundland fell radically short in a key safety test. According to certification documents from the U.S. Federal Aviation Administration, the main gearbox of the Sikorsky S-92 failed just 10 minutes into a test designed to prove that it could run for at least half an hour without oil.
The S-92's run-dry capabilities have played a prominent role in the continuing investigation of a crash that killed 17 people last March. An S-92 owned by Cougar Helicopters plunged into the Atlantic en route to an offshore oil platform. Just minutes before the crash, the pilots made a mayday call after cockpit gauges warned of falling oil pressure in the S-92's main gearbox.
The newly released FAA documents detail how the S-92 was certified under an advanced safety standard known as FAR Part 29, even though it failed the run-dry test. According to the documents, Sikorsky argued that the chances of gearbox oil loss were "extremely remote," and that the S-92 should be certified under a clause that allowed an exemption from the 30-minute run-dry requirement.
The new documents outline an ongoing discussion between American and European aviation regulators over the safety of the helicopter's all-important main gearbox. European officials noted that the S-92's transmission survived for just 10 minutes after its oil was rapidly drained - only one third of the time called for by the FAR 29 standard. The European regulators concluded that loss of oil would mean the helicopter could only stay in the air for "around 10 minutes."
A number of aviation experts, including helicopter test pilots, believe the Cougar pilots involved in the fatal crash were given a false sense of security by the S-92's certification to the FAR 29 standard and its call for a 30-minute run-dry capability. "They thought they had more time than they did," one pilot said.
Sikorsky has repeatedly defended the way the S-92 was certified, and denies that pilots and operators were given misleading impressions about its run-dry capabilities.
Spokesman Paul Jackson noted that the S-92 flight manual tells pilots to land immediately if the main gearbox loses oil pressure. Mr. Jackson has also denied that Sikorsky claimed a 30-minute run-dry capability for the S-92.
But documents obtained by The Globe and Mail show that run-dry was once touted by the company as a key S-92 feature.
The S-92's run-dry capabilities were highlighted in a Globe and Mail investigation shortly after the crash. The investigation revealed that Sikorsky got the S-92 certified after it persuaded aviation regulators that the chances of oil loss were "extremely remote" - a standard that means the statistical chance of failure is approximately one in every 10 million flight hours.
But the Globe investigation revealed a failure rate 267 times worse than that standard.
The newly obtained FAA documents show that Sikorsky came up with a work-around solution after the S-92 failed the 30-minute run-dry test. After an extensive engineering analysis, Sikorsky determined that the only clear risk of a major gearbox oil leak came from an oil cooler that fed into it. To eliminate the problem, Sikorsky came up with a bypass valve that would allow pilots to divert oil from the cooler in the event of a leak.
In a 2002 test, the S-92 gearbox ran for hours after the oil cooler bypass system was activated. But in the real world, the S-92's transmission developed leaks from an unexpected source. Titanium studs that held the transmission's oil filter in place broke in flight, allowing rapid oil loss. Investigators with the Transportation Safety Board of Canada found broken studs after recovering the wreckage of the S-92 that went down off Newfoundland in January, and aviation safety officials ordered changes to every S-92 in service.