When the Canadian government placed a $5-billion order for 28 Sikorsky S-92s in 2004, the model was touted as "the safest helicopter in the world," with an advanced design certified to tough safety standards that made it ideal for risky offshore operations. But a crash that killed 17 people off Newfoundland last month is raising questions about the safety of the S-92.
Documents obtained by The Globe and Mail show that the S-92 failed a critical test of whether the aircraft can keep flying if the oil in its main gearbox leaks out, a key safety feature found in other makes of helicopter - including a model that was beaten out by the Sikorsky for the Canadian military contract. The delivery of the helicopters to the Department of National Defence has already been beset by a series of delays.
Certification documents show that the S-92 couldn't meet a specification that calls for the main gearbox to run for half an hour without oil - a requirement known as "run dry." The specification is designed to give pilots extra time to make a safe landing if the gearbox loses its oil.
That is considered one of the deadliest emergencies a helicopter pilot can face, since it can cause a transmission seizure that stops the rotor blades.
"There's not much worse that can happen," says Shawn Coyle, a U.S.-based test pilot who has flown 55 types of helicopter. "If the rotors stop, it's all over."
Although many older helicopters can survive for only a few minutes without gearbox lubrication, the Sikorsky S-92 is certified to an advanced standard called Federal Aviation Regulation (FAR) 29, which calls for a run-dry time of 30 minutes. But certification documents filed with the Joint Aviation Authorities, the European counterpart to the U.S. Federal Aviation Administration, show that the S-92 couldn't meet the specification. Instead, the Sikorsky was certified under a clause that allows an exemption if the chances of gearbox oil loss are "extremely remote."
With only 100 S-92s sold worldwide, there has already been one documented case of total oil loss, and it is the leading theory in last month's S-92 crash off the coast of Newfoundland. "Two cases in five years is not what I would call an extremely remote chance," says an aerospace engineer who has followed the S-92. "One in five million is remote."
The first known case of total oil loss with an S-92 happened in the summer of 2008, when an Australian S-92 made a forced landing after the pilots noticed that the gearbox oil pressure had fallen. The S-92 landed safely within eight minutes. Accident investigators quickly pinpointed the cause: The oil filter on the main gearbox had worked loose, letting the gearbox oil escape. The failure was attributed to unexpected wear on three titanium studs that connect the oil-filter assembly to the main gearbox. Investigators found similar damage on the S-92 that crashed last month off Newfoundland.
The crash of a Cougar Helicopters flight has sparked intense debate among pilots, who have focused on what appears to be a key contradiction: The S-92 is certified to a standard that appears to give the pilots half an hour to make a landing if the gearbox runs dry, but the helicopter isn't capable of it - instead, it was approved on the assumption that complete oil loss is near impossible.
Mr. Coyle, a certified test pilot who has worked for Bell Helicopter and Transport Canada and has logged more than 7,400 hours in the air, said few pilots would be aware of the distinction that allowed the S-92 to pass FAR 29 without actually meeting the run-dry requirement. "If you'd asked me three weeks ago, I would have said that there was half an hour," he says. "Now I know different."
Although the S-92 flight manual instructs pilots to land immediately if they lose oil pressure in the main gearbox, the actions of the flight crew in the Newfoundland crash on March 12 suggest that they thought they had more time than they did.
After radioing a mayday in which they reported gearbox oil-pressure problems, they spent approximately eight minutes descending from 9,000 feet to about 800, where they apparently levelled off for several more minutes. Although the investigation is ongoing, many pilots and engineers believe the S-92's gearbox seized, dropping the helicopter into the Atlantic when the rotor blades stopped.
Experienced pilots say the crew could have made it from 9,000 feet to the water in less than half the time they took. "To me, the descent rate says they thought they had a longer window," says a former offshore helicopter pilot.
According to the JAA documents, the S-92 passed certification after Sikorsky, an American company based in Connecticut, demonstrated that a complete loss of gearbox oil was nearly impossible. The S-92 was also approved by the FAA, which refused to release any of the gearbox test results, but indicated that the S-92 did not run completely dry when it met the standard: "The specifics of how Sikorsky met the provisions of [the regulation]are proprietary," says spokesman Les Dorr.
A helicopter's main gearbox, which transmits engine power to the rotor blades, is one of the most critical components in the aircraft - if the gearbox seizes, the rotor stops turning, and the helicopter falls out of the sky. The stresses inside a helicopter gearbox are enormous, particularly in a large helicopter like the S-92, which has two turbine engines and rotor blades that span 17 metres - wider than an NBA basketball court.
Pilots of older designs, like Canada's notorious Sea Kings, know that their machines can fall out of the sky quickly if they lose gearbox oil pressure. Many are equipped with dual warning systems, to ensure that pilots get some warning before the gearbox seizes. Pilots are trained to get down as quickly as possible if they see an oil-pressure warning: "You look at what's underneath you, and that's where you go," says a pilot who spent several years in the offshore-oil industry.
The introduction of FAR 29 and its 30-minute run-dry requirement in the late 1980s presented engineers with a serious challenge. "Making a helicopter transmission survive without oil is one of the toughest jobs there is," says one aerospace engineer.
Several competitor's helicopters have passed the run-dry test, including archrival Augusta Westland's EH-101, which was once chosen by the Canadian government as a maritime-patrol helicopter to replace the aging Sea King, only to be pushed aside in favour of the S-92 variant named the CH-148. The Eurocopter EC-225 passed the dry-run test after engineers added a backup system that sprayed the gears with coolant if the oil leaked.
Sikorsky representatives said they could not discuss any specifics of the S-92's gearbox, or its compliance with the run-dry standard, due to the ongoing investigation into the Newfoundland crash:
"Sikorsky is continuing to assist in the investigation," said spokesman Paul Jackson. "Since that investigation remains ongoing and the gearbox has been identified as an area of focus, I cannot comment on any matters related to it."
Cougar Helicopters spokesmen did not respond to interview requests, but one employee said the company has continued faith in the Sikorsky S-92: "It's a great helicopter," he said.
Mr. Coyle, the test pilot, said Cougar is known in the industry for its professionalism and unrelenting maintenance standards: "They fly in some of the world's toughest conditions, and they do a great job at it. What happened here is unbelievably sad."