On 10 May 2012, a Eurocopter EC225 making a 150nm passenger flight from Aberdeen to the Maersk Resilient Offshore Platform in the North Sea in day Visual Meteorological Conditions (VMC) was in the cruise at an altitude of 3000 feet with the AP engaged when there was a sudden warning of failure of the main gearbox (MGB) lubrication system and soon afterwards, another warning indicating failure of the emergency lubrication system. A controlled ditching was completed in benign conditions and, with the Emergency Flotation System functioning normally the 14 occupants evacuated into one of the life rafts. Two occupants sustained minor injuries whilst evacuating; six were subsequently rescued by a SAR helicopter and the remainder were transferred to a lifeboat.
An Investigation was carried out by the UK AAIB. It was established that the helicopter had been was in the cruise at an altitude of 3000 feet with First Officer as PF and the AP engaged. When 34nm east of Aberdeen, an indication of low oil pressure was annunciated for the main gearbox (MGB). The crew activated the emergency lubrication system in accordance with the required procedure but shortly afterwards, a further warning was also display indicating that this system was inoperative. The associated procedure in this situation is to land immediately so the aircraft commander briefed the passengers, took control and carried out a successful ditching. The total flight time was 27 minutes.
The helicopter remained upright, supported by its Helicopter Emergency Floatation System (EFS) and after the engines had been shut down and the rotors stopped, all occupants evacuated the helicopter into one of the life rafts using the right hand cabin door. Six were subsequently rescued from the raft by a SAR helicopter and the other eight were transferred to a lifeboat.
Three Special Bulletins were published during the initial stages of the Investigation and it was progressively established that although there had been a catastrophic mechanical failure causing the MGB to fail, the emergency lubrication system had, despite the contrary indication available to the crew, had been functioning normally throughout. It was noted that “this was the first time the MGB emergency lubrication system on the EC225 LP had been activated operationally” and stated that it had been found that a bleed air pressure sensor could generate a false indication of failure for the emergency lubrication system even if it functioning was within the required tolerance.
In a Safety Bulletin issued on 17 October, a Safety Recommendation was accordingly issued as follows:
- that the European Aviation Safety Agency requires Eurocopter to review the design of the main gearbox emergency lubrication system on the EC225 LP Super Puma to ensure that the system will provide the crew with an accurate indication of its status when activated. [2012-034]
When, shortly after this finding had been announced and the corresponding Safety Recommendation made in Special Bulletin S5/2012, another EC225 LP helicopter had ditched in similar circumstances, involving only the second case of an MGB emergency lubrication system on an EC225 LP being activated operationally, this also became the subject of a UK AAIB Investigation. It was soon found that the system issues appeared to be closely related but also that the airworthiness response to the first event had been insufficient to prevent the second. Consequently, it was announced on 29 November 2012 that the two Investigations had been combined because of the essential similar airworthiness issues raised. The three earlier Special Bulletins have since been followed by two more dealing with the progress of the combined Investigation, which is continuing.
On 18 March 2013, the issue of a Special Bulletin concerned problems which had been encountered after each ditching with effective deployment of the Crash Position Indicator (CPI). Action being taken by Eurocopter to resolve the matter in respect of the EC225 was noted but since the same type of Automatically Deployable Emergency Locator Transmitter (ADELT) device is also fitted to several other aircraft types not addressed by actions taken in respect of the EC225, two more Safety Recommendations were therefore issued:
- that the European Aviation Safety Agency requires the manufacturers of aircraft equipped with a Type 15-503 Crash Position Indicator system, or similar Automatically Deployable Emergency Locator Transmitter, to review and amend, if necessary, the respective Flight Manuals to ensure they contain information about any features that could inhibit automatic deployment. [2013-006]
- that the Federal Aviation Administration requires the manufacturers of aircraft equipped with a Type 15-503 Crash Position Indicator system, or similar Automatically Deployable Emergency Locator Transmitter, to review and amend, if necessary, the respective Flight Manuals to ensure they contain information about any features that could inhibit automatic deployment. [2013-007]
This Bulletin also confirmed the finding that both MGB oil losses had occurred because of the fracture of the bevel gear vertical shaft and that the most likely cause of both emergency lubrication system false failure annunciations had been a consequence of an error by Eurocopter in the specification issued to the manufacturer of a related pressure switch.
Since it was the false indication that the emergency MGB lubrication system had failed that was the reason both helicopters had been ditched, it was noted that Eurocopter had issued an Alert Service Bulletin (ASB) on 22 February 2013 requiring the modification of pressures switch wiring to fix the problem and that this ASB had then been mandated by an EASA AD 2013-0037 the same day.
The Investigation is continuing and an independent review of the fracture mechanics to establish why both these shafts failed during normal operations is being carried out. It is not yet certain that the root causes of the failure of the both shafts occurred for the same reasons.
The Investigation so far is covered by Special Bulletins as follows:
- S3/2012, published on 13 July 2012
- S5/2012, published on 17 October 2012
- S7/2012, published on 29 November 2012
- S2/2013, published on 18 March 2013 and containing Safety Recommendations 2013-006 and 2013-007