EC 225 CHC Helikoper Bergen

2.5.5 The AIBN is aware that one should be careful to pass a critical judgement of the adequacy of the actions taken following the G-REDL accident, based on the hindsight created by the knowledge we have after LN-OJF. The actions made by the manufacturer and the authorities in the aftermath of G-REDL were based on the available knowledge and circumstances at the time. This knowledge was naturally limited for several reasons; most importantly, key elements of information were missing due to the fact that not all gear parts were recovered.
2.5.6 It is, however, the mandate of the safety investigation authority to assess how and why two similar catastrophic accidents could happen only seven years apart to near identical helicopters

2.5.8.1 A more detailed assessment of the actions in response to the safety recommendations, and how they were documented and closed by EASA and Airbus Helicopters will follow in the final report.

3.1 The main areas for the AIBN’s further investigation are:
- The AIBN will continue with the metallurgical examinations and, in conjunction with Airbus Helicopters, as far as practicable seek to understand the underlying driving mechanisms of the fatigue fracture. This includes:
 assessment of a possible connection between the fatigue and the differences in the two planet gear configurations approved for the gearbox.
 detailed examination of the area where the fatigue crack is assumed to have initiated.
 examination of the recently salvaged second stage planet carrier with the inner race from the fractured planet gear and the lower rotor mast bearing.
- The observed failure mode in this accident seems to differ from what was expected or foreseen during the design and certification of the main rotor gearbox. The certification process and Certification Specifications for Large Rotorcraft related to catastrophic failure and requirements for safety barriers will be subject to further investigation.
- The AIBN will continue the investigation into how and why two similar catastrophic accidents could happen to near identical helicopters only seven years apart. Further assessment of the follow-up on the G-REDL safety recommendations and the continuing airworthiness of the gearbox after 2009 is a relevant issue.
This work requires good collaboration with the responsible entities, primarily the helicopter manufacturer and the EASA, and unhampered access to relevant documentation.

1.        Airbus Helicopters notes the publication of the preliminary report by the AIBN to mark the first anniversary of the H225 accident, which claimed the lives of 13 people off Turøy in Norway. We wish to express our deep regret at this tragedy, and again, we offer our sincere and profound sympathies to the bereaved families.
2.        Since the accident, we have been providing our full and complete support to the investigation. We have had regular technical meetings with the authorities as well as with all relevant helicopter industry bodies. We look forward to every opportunity to discuss with them the safety recommendations and technical points arising from the report. We are totally committed to transparency in all matters regarding aviation safety and international helicopter regulations. Indeed, it is the essence of what we do.
3.        In the course of the AIBN investigation, additional elements brought by the 2016 accident showed that there were mechanical similarities between the 2016 accident and an earlier one, in 2009. We were not aware of any related issue at the time of the 2016 accident.
4.        The information available to us from the 2016 accident has allowed us to take protective measures that we could unfortunately not have put in place in 2009 based on the knowledge and evidence available at the time, and also because significant parts from the 2009 accident were never recovered.
5.        We will continue to work with the European Aviation Safety Agency (EASA) and to comply with EASA airworthiness requirements. In the course of the investigation into the 2016 accident, we have implemented a set of protective measures which have been requested and validated by EASA. Nothing in this preliminary report alters this.
6.        We are using lessons learned from the ongoing investigations into the 2016 accident to set new standards for the helicopter industry. As part of these efforts, we are also looking to improve working practices across the sector.

The new epicyclic module in the AS 332 L2 had an architecture based on the AS 332 L1, but was fitted with 8 planet gears instead of the previous 9, while the diameter of each gear increased. Specifically, the focus was on limiting spalling on the inner raceway, as this had been a problem with the AS 332 L1. L10 life4 was not specified by Airbus Helicopters, but according to Airbus Helicopters it was included in the proposals from the suppliers. The specific proposals from the suppliers are unknown to this investigation as Airbus Helicopters has not been able to retrieve the documentation.

Since EASA AD 2017-0050-E was issued, AH designed for the EC 225 LP helicopters a Full Flow Magnetic Plug (FFMP) device enabling collection of MGB particles upstream of the oil cooler (MOD 07 53047), and in addition, a revised repetitive inspection regime. AH also streamlined the concept of maintenance of the MGB, which resulted in the need to further revise life limits for the second stage planet gear of the MGB. AH issued AS332 Emergency ASB 05.01.07 and EC225 ASB 05A049 as separate documents at Revision 5.