European safety regulators have grounded the region’s fleets of Airbus Helicopters H225 and AS332 L2 rotorcraft after evidence emerged of a potentially catastrophic gearbox fault afflicting both types.
The European Aviation Safety Agency emergency airworthiness directive (EAD), issued on 2 June, comes on the back of the fatal 29 April crash of a H225 (LN-OJF) on the coast of Norway in which 13 passengers and crew died after the main rotor separated from the rest of the aircraft.
Investigators had narrowed down their inquiry to three components – the gearbox suspension bars, the conical gearbox housing, and the main gearbox epicyclic module.
EASA identifies a potential issue with the latter component as the reason for its grounding order. It cites the ongoing Norwegian investigation which found “metallurgical findings of fatigue and surface degradation in the outer race of a second stage planet gear” in the epicyclic module.
A 1 June preliminary report from Norway’s SHT accident investigation branch says it found “features strongly consistent with fatigue” on recovered sections of a second stage gear. This, it says, appears to have originated in the outer race of the bearing – effectively the inner surface of the part – “propagating towards the web of gear teeth”. It also indicates there is “evidence of spalling” – or degradation of the bearing surface.
It adds: “The nature of the catastrophic failure of the LN-OJF main rotor system indicates that the current means to detect a failure in advance are not effective.” It also calls on EASA to take preventative action.
Although the safety agency cautions that it is not yet possible to determine “if this is a contributing causal factor or subsequent failure from another initiating factor”, it has nonetheless ordered the grounding.
Suggestions that the epicyclic module might be at fault emerged soon after the accident due to its striking similarity to a fatal crash of an AS332 L2 (G-REDL) in 2009 in which the same part failed.
But the manufacturer had attempted to play down possible links, instead focusing on the failure of the gearbox suspension bars as the most likely cause for the rotor separation.
However, the evidence of spalling – the process which initiated the gearbox break up in the crash of G-REDL – seems to add weight to the connection between the two disasters.
Airbus Helicopters say that in the light of the new findings it “supports EASA’s cautious approach” and remains committed supporting the investigation and its customers “while working with the wider industry to ensure safety”.
In addition, a separate EAD issued on 1 June calls for the replacement of the attachment hardware and base plate fittings of the main gearbox suspension bars.
H225s and AS332 L2s had already been grounded in the UK and Norway following the crash. The wider order also does not apply to examples used for military of parapublic missions.