The Accident Investigation Board of Norway (AIBN) has released a preliminary report into the fatal accident involving CHC Helicopters H225 (EC225LP), LN-OJF, near Turoy, Norway on April 29, issuing an urgent safety recommendation to the European Aviation Safety Agency (EASA) concerning the type’s main gearbox (MGB).
Metallurgical findings during the investigation found features strongly consistent with fatigue in the outer race of a second stage planet gear in the epicyclic module of the MGB.
“It cannot be ruled out that this signifies a possible safety issue that can affect other MGBs of the same type,” said the AIBN’s report published on June 1. “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. The AIBN therefore recommends that EASA take immediate action to ensure the safety of the Airbus Helicopters H225 main gearbox.”
On June 2, EASA announced the prohibition of all flights by the Airbus Helicopters H225/EC225LP and AS332L2 helicopters as a precautionary measure and also issued another Emergency Airworthiness Directive (EAD) that required further inspection and replacement instructions to ensure the correct installation of the type’s MGB suspension bars and attachment fittings.
The directive followed an earlier EAD, issued four days after the accident, that required a number one-off precautionary inspections of the type’s MGB. In carrying out the original EAD, some operators reported to EASA they found tightening torque values on the attachment bolts of the MGB’s three suspension bars were out of tolerance, plus detected some incorrectly positioned washers in the fitting assemblies.
Immediately after the release of the preliminary report, the Civil Aviation Authority of Norway and the UK’s Civil Aviation Authority extended their ban to allH225/EC225 LP and AS332 L2 flights including search and rescue (SAR) operations.
In a statement, Airbus Helicopters said: “In light of new findings from the AIBN’s preliminary accident investigation report, Airbus Helicopters supports EASA’s cautious approach. We continue to fully support the AIBN, EASA, our customers and the ongoing investigation by providing information in full transparency, while working with the wider industry to ensure safety.”
The investigation into the exact cause of why the main rotor hub detached from the fuselage continues.
