Eurocopter says it has made significant progress in solving the main gearbox issue that has blighted the EC225 medium twin since last May, reporting that a third test campaign at its headquarters in Marignane, France “is establishing” the cause of crack initiation.
Eurocopter attributes the issue to “a combination of factors” leading to a degradation of the vertical shaft’s fatigue resistance. The helicopter manufacturer has excluded any “abnormal dynamic overload.” Failure of the bevel gear shaft causes a loss of lubrication.
Two EC225s ditched last year (on May 10 and October 22) and the crack initiations for both have been reproduced on test benches. The crack propagation model has been verified in bench tests as well. The conclusions, however, still need to be “discussed with the investigation authorities and Georgia Technology Research Institute,” according to Eurocopter. A flight-test regimen is being prepared to further study the propagation phase.
Eurocopter engineers had already found the root cause and a fix for the false-alarm problem with the emergency lubrication system. EC225s are still effectively grounded in the North Sea area.