July 09, 2013
Oil and gas operators could return their Eurocopter EC225s to service within weeks now that the European Aviation Safety Agency (EASA) has certified fixes to the bevel gear vertical shaft, a critical component in the main gearbox that drives lubrication pumps.
The July 9 clearance by EASA ends a nine-month grounding of more than half the worldwide fleet of EC225 and EC725 helicopters imposed after air accident investigators concluded that two ditchings into the North Sea by U.K. operators — Bond Offshore in May 2012, and CHC in October 2012 — were caused by the failure of the bevel gear vertical shaft.
In its announcement, EASA says Eurocopter’s solution reduces the “likelihood of any shaft crack initiation,” and that while it is satisfied that the changes ensured “safe and airworthy operations of the EC225 type,” it may update its directive based on further investigation.
Eurocopter says the crack can only appear during an “unlikely combination of factors,” and that this “explains why it appeared only after seven years and 300,000 flight hours for the EC225/725 fleet.”
The manufacturer’s four interim fixes, as previously reported by Aviation Week, include a new shaft-cleaning procedure that removes mud generated by the wear of the gearbox splines in the localized humid environment on the shaft. The company says this would “significantly reduce the possibility of active corrosion and the likelihood of crack initiation.”
This measure will be enhanced with the addition of new oil jets.
To help detect cracks, EASA has approved the use of an ultrasonic non-destructive inspection (NDI) as an alternative to the eddy current method now in use. Company documents suggest tests should take place every 8-10 hr. Eurocopter says training on the new method will be provided for free.
The primary interim fix, however, is real-time monitoring of the shaft using an update to the aircraft’s onboard health and usage monitoring system, known an M-ARMS. When fitted, the modification — dubbed Mod 45 — will issue an onboard cockpit amber warning if vibration levels indicate the presence of a crack. In the event of a warning, the aircraft will be able to continue to safely operate for sufficient flight time to permit the pilot to return to base or perform a normal landing.
Eurocopter has tested the system in flight using a pre-cracked gearbox, flying the aircraft to the point of failure as part of the certification process.