A European aviation safety regulator is issuing an emergency directive about the same model of Sikorsky helicopter involved in a fatal crash off Newfoundland, saying cracks have been found in the main gearbox mounting that could lead to loss of control of the helicopter.
The European Aviation Safety Agency, based in Germany, issued the airworthiness directive Friday, saying that the mounting feet for the Sikorsky S-92s would have to be given "repetitive inspections" by the operators to insure cracks aren't developing.
Earlier this year, the entire S-92A fleet was grounded after the crash off Newfoundland of Cougar Flight 491 in which 17 people died.
The Transportation Safety Board of Canada is still investigating the crash, but it has said titanium mounting studs that attach an oil filter bowl assembly to the main gearbox broke during the flight.
The board has said the pilots of the helicopter indicated there was a problem with the main gearbox oil pressure about 13 minutes into the flight. Less than 10 minutes later, it plummeted into the ocean.
The titanium studs have since been replaced with steel under a directive issued by the U.S. Federal Aviation Administration.
The directive issued Friday says "cracks have reportedly been found" in the mounting feet of the gearbox, and that in one instance the mounting foot was completely severed from the main gearbox.
It says this condition, if it isn't detected and corrected, could lead to the main gearbox being detached and the loss of control of the aircraft.
The document requires that there be "repetitive inspections of the main gearbox mounting feet pad...for cracks and if any cracks are found, the replacement of the main gearbox assembly with a serviceable unit."
However, even after the replacement, the safety agency says that frequent inspections will be needed for every 10 hours of flight.
Friday's emergency directive comes after Sikorsky sent an Oct. 7 letter to its S-92 operators, saying cracks have appeared in footing bolts that attach the main gearbox to the S-92s fuselage.
The reported cracks have occurred only on S-92s that ferry European offshore works to platforms in the North Sea.
Paul Jackson, a spokesman for Sikorsky, a U.S.-based subsidiary of United Technologies Corp., said his company had already informed operators of the cracks in its own safety directive.
"We believe the inspection intervals spelled out in our bulletin to operators last month are appropriate, but we certainly appreciate the European Aviation Safety Agency's heightened requirements," he said in an email.
"The more attention on safety awareness, the better. We are continuing to work with the affected customers to determine root cause of this problem and correct it as quickly as possible."
"In the meantime, customers are flying and maintaining normal operations."