The Airbus Helicopters H225 and AS332L2 remain under scrutiny after the H225 accident that claimed 13 lives on April 29. On that day, a CHC-operated H225 crashed near Bergen, Norway, as it was flying back from the Gullfaks B oil platform. The EASA has required inspections. Norway and the UK have suspended H225 and AS332L2 Super Puma commercial flights.
Investigators of the Norwegian air accident bureau (AIBN) are trying to determine how the main rotor detached in flight. This also happened in 2009 on a Bond-operated AS332L2 Super Puma in the UK North Sea. In that accident, the AAIB identified rupture of the main gearbox epicyclic module case as the cause of the rotor detachment. Investigators identified issues with design and maintenance as the cause.
Two weeks after the UK CAA and its Norwegian counterpart prohibited H225 commercial flights, they extended the grounding to the AS332L2. They cited “the close similarities between the two types.” The restrictions do not apply to search-and-rescue flights.
Almost simultaneously, on May 13, the AIBN published a preliminary report. The investigation is focusing on the main rotor assembly: the suspension bars (aka lift struts), the gearbox and the rotor head. At the time, investigators had found no obvious signs of fatigue but had not yet begun metallurgical testing. They were still collecting wreckage at the crash site.
Less than a week after the latest accident, the AIBN ruled out “human error on board.” As a result, Airbus Helicopters said investigators should look to design, production or maintenance for the cause. The airframer, after preliminary examination of the vertical shaft that drives oil pumps, believes the cause is different from the issue behind two serious incidents in 2012, a problem that has since been resolved through the replacement of certain serial-numbered main gearbox (MGB) bevel gear vertical shafts and replacement, if necessary, of each MGB bevel gear vertical shaft. Therefore, Airbus Helicopters quickly said its decision was “not to suspend flights of any nature for the EC225LP” [H225].
On May 3 the EASA issued an emergency AD, requiring inspections of the H225 before any further flight. The installation of the three suspension bars located around the main rotor assembly must be checked. The chip detectors of the main gearbox, as well as the oil filter, must be checked for absence of metallic particles. According to the AAIB, detection and identification of such particles could have prevented the 2009 accident. The third step of the mandated inspection is, for those helicopters equipped with the M’arms vibration health monitoring system (the H225’s Hums), to download data and check for any threshold exceedance.