Eurocopter Identifies EC225 Gear Bevel Shaft Cracking
Eurocopter "now fully understands the root cause of the cracking and need to go to validation of both the final and immediate fix," said outgoing President and CEO Lutz Bertling at the company's headquarters in Marignane on April 18. He was addressing the problem with the main gear bevel shaft that has been identified as the "root cause of the crack initiation" that lay behind the May 10 and Oct. 22, 2012 ditchings of EC225 Super Pumas in the North Sea, owned respectively by Bond Offshore Helicopters and CHC Scotia Helicopters.
"The final fix will include a partial redesign of the shaft within the same forged part. There is a residual stress caused by the manufacture process and when combined with corrosion," explained Bertling. "In the history of the company we have never had a technical issue that has impacted so much," he added.
The timeframe to get the type back into operation depends on the progress of discussions currently underway with the authorities, but Bertling believes it will be no later than the third business quarter of the year, although previous expectations for a return to service date have slipped.
Janick Blanc, head of the EC225/725 program, expanded on Eurocopter's findings, declaring that the failure was not due to a "unique cause but a combination of three factors." Rotor & Wing understands these to include the initial manufacturing process together with water ingestion, which can cause corrosion. Said Blanc: "Eurocopter engineers have been able to reproduce the cracking in their laboratories and can induce the crack propagation."
Blanc revealed that the company had created the crack propagation in "eight shafts" and that they could now create the conditions for it to occur and were conducting flight trials to measure the rate of propagation.
"We are now in the process of communicating the findings to the authorities," said Blanc. He added that a short-term fix involved the development of software and the installation of a couple of warning lights in the cockpit, but that no further additions or sensors to the existing health and usage monitoring system (HUMS) was required. This fix was being validated and certified through the European Aviation Safety Agency (EASA).
"We are providing all the data that we have to the authorities and meetings are taking place continuously," said Blanc. "We've had good exchanges with EASA, and we are confident that we will have an outcome sometime in May."
The implementation will be free to operators. Eurocopter's results have still to be validated by the Air Accidents Investigation Branch (AAIB) and EASA.  - By Andrew Drwiega, International Bureau Chief