European safety regulators have lifted the grounding order on Airbus Helicopters Super Puma rotorcraft imposed in the wake of a fatal crash earlier this year, but separate flight bans in the UK and Norway remain in force.
A total of 13 passengers and crew died when the main rotor separated from the rest of a H225 helicopter (LN-OJF) near Turøy on Norway’s west coast on 29 April.
A subsequent report issued on 1 June by Norway’s SHT air accident investigation agency narrowed the cause to the disintegration of the second-stage planet gear in the main gearbox epicyclic module. It blamed this on a fatigue crack initiated by spalling – the disintegration of a bearing surface.
In a response the following day, the European Aviation Safety Agency said it had decided “as an additional precautionary measure” to “temporarily ground the fleet” by prohibiting flights of all civil H225 and AS332 L2 helicopters.
EASA says that although the “root cause of this failure is still not fully understood” by Airbus Helicopters, it is confident that with a number of steps put in place by the manufacture,r the Super Puma is now safe to return to service.
Key among these is the replacement of one of the two configurations of planet gear. A review of in-service data showed that “one configuration has higher operating stress levels that result[s] in more frequent events of spalling… while the other exhibits better reliability behaviour,” says EASA.
The two designs are made by separate manufacturers. Airbus Helicopters has not revealed which supplier’s product has proved less reliable, but stresses that both were designed to its specifications.
EASA says that by limiting the gear configuration to the more reliable version, plus reducing inspections of the particle chip detector and main gearbox oil filters to intervals of 10 flight hours, “an acceptable level of safety can be restored”.
In addition, it has reduced the service life of the remaining planet gear design, as well as mandating the replacement of the part if it has been involved in an unusual event such as a lightning strike or road accident during transit.
SHT had noted that the main gearbox fitted to the ill-fated H225 had been involved in an incident during transportation, but had not identified a positive link with the Turøy crash.
However, the flight restrictions imposed by the regulators in both Norway and the UK are still in place.
The UK Civil Aviation Authority says it is “united in [its] approach” with its Norwegian counterpart. “Both agencies now await further information from the accident investigation before considering any future action,” it says.
Airbus Helicopters adds: “We are providing assistance to our customers and working with related stakeholders in order to help them return their aircraft to service at the appropriate time.
“Meanwhile, we maintain our full support to the AIBN in the frame of the ongoing investigation.”