Incorrect specifications supplied to a company manufacturing the pressure switches used in the emergency lubrication system of certain Eurocopter EC225s resulted in an erroneous failure message being displayed to two crews, who subsequently ditched in the North Sea.
The latest update on the incidents in May and October last year issued by the UK's Air Accidents Investigation Branch reveals that the crews of both helicopters - G-REDW and G-CHCN, respectively - received the warning message indicating a failure in the main gearbox emergency lubrication system around 30s after it was activated.
Although the primary lubrication system had ceased operating in both cases due to a fractured drive shaft, the back-up system was working correctly, the AAIB says.
However, standard operating procedure mandates an immediate landing if the emergency system fails. This was safely performed in both cases.
The AAIB says the fault, introduced when Eurocopter modified the system in 2010, was "the most likely cause" of the incorrect warning displayed during the accidents. It also identified an issue with the crash position indicators fitted to both aircraft, with the manufacturer now taking action to resolve this, it says.
Eurocopter is yet to identify the root cause behind the fractures of the bevel gear vertical shaft at fault in both accidents. As a result, over-water flights of the type are still restricted in both the UK and Norway, with operators elsewhere taking a similarly cautious view.
Although a third campaign of testing on the component has been completed, the manufacturer is yet to release the results.
The airframer could also still face compensation claims from EC225 operators struggling with disruption to their services as a result of the effective groundings in force.
CHC Helicopter - parent company of CHC Scotia, the operator of G-CHCN - warns in its latest financial statements that it "preserve[s] our rights to recover any losses we may experience" from the restrictions in place, although it notes that no material impact was felt during the quarter to 31 January.
However, fellow EC225 operator ERA Helicopters highlighted in its full-year results on 27 February the difficulties it could face. "With no definitive timeline in place for the EC225 to return to service, a reduction or cancellation of customer contracts for those EC225 helicopters that we operate and for those operated by our contract-lease customers around the world could have an adverse effect on our financial results," it says.
It has been forced to return to service a number of parked AgustaWestland AW139s in order to support its offshore operations in Brazil. "During this challenging time, the operational capabilities of the AW139 helicopter have been demonstrated with great effect in serving to fill the needs of our EC225 customers," it says.