The company says that with the detection methods in place, the probability of a bevel gear crack going undetected by M-ARMS or NDI is now lower than 109/FH, or one per billion, which the company says is “more severe than the certification standards.”
Eurocopter says that while shaft ruptures can be eliminated, the risk of finding a crack can not, so it is developing a new bevel gear vertical shaft that will feature improvements in surface, finish, lubrication and geometry to avoid what the manufacturer calls “corrosion accretion.”
The design will also eliminate stress hot spots, which engineers say was one of the factors for the failure of the original design. The new shaft will also be thicker, but it is not clear if the component comes with a weight penalty.
According to Eurocopter, the new shaft will be available for retrofit in the second half of 2014, and will eliminate the need for the interim fixes.
The U.K. Civil Aviation Authority says it will amend its operational restrictions on each aircraft once the requirements of the EASA directives are met.
Operators have welcomed the decision. A spokesman for Bond Offshore Helicopters says, “This is an important step forward in the validation of the safety measures proposed by Eurocopter by the airworthiness authorities. Bond continues to work with Eurocopter, the regulators, our oil and gas industry customers and other operators to achieve a safe return to flying operations for the aircraft.”
A CHC spokeswoman, meanwhile, says, “Today’s action is an important step forward for industry toward the safe return of the EC225 aircraft to fly overwater service. We are continuing with careful and thorough preparations for resuming such flights pending additional regulatory approvals.”