Fell 20 Minutes Short Of Gearbox Failure Requirement

During the certification process for the Sikorsky S-92A, documents show that the aircraft failed a crucial test in which all the oil is drained from the main gearbox to simulate a loss of oil during flight. The test aircraft gearbox failed after about 10 minutes, which is 20 minutes short of the FAA standard.

A Sikorsky S-92A went down in March near Halifax, Nova Scotia, and 17 people on board the aircraft were lost. Oil loss from the gearbox is being considered as a factor in the accident.

Sikorsky and the FAA say the aircraft was certified after a bypass valve was installed that would divert oil to the gearbox in the event of a catastrophic leak, but that bypass is manually activated by the pilot. A second aircraft was tested with the bypass installed and activated, and the system performed well.  The gearbox did not fail after several hours of testing. 

The Canadian News Service reports that documents obtained through a Freedom of Information Act request show that Sikorsky and the FAA agreed that the single point of failure for an oil leak was the oil intercooler that feeds the gearbox, and that the risk of a system failure due to a gearbox housing leak was "extremely unlikely. After the bypass test was successful, the S-92A was certified by the FAA and EASA.

Sikorsky spokesman Paul Jackson said in an e-mail that the company had demonstrated to both the FAA and EASA that the installation of the bypass valve "addressed the only identified, non-extremely remote possibility for a main gearbox oil leak. It is very important to note that while the Cougar accident was indeed a very tragic event, the worldwide S-92 fleet has about 185,000 operational hours without any other incidents involving this injury."

Some people familiar with the helicopter, including retired pilot Per Gram who conducted tests on the S-92 for Norway, said the FAA should not have certified the aircraft after learning of the first test. "I disagree fully with the FAA for allowing Sikorsky to pass that test on that basis," he said, referring to the second test of the bypass valve.

File Photo

The NTSB is still investigating the accident. It said that studs had broken on an oil filter attached to the main gearbox, resulting in the loss of a large quantity of oil.  The engine ran for 10 minutes and 47 seconds after the oil loss.

FMI: www.ntsb.gov, www.faa.gov, www.sikorsy.com