On 22 October 2012, a Eurocopter EC225 LP on 226nm passenger flight from Aberdeen to the West Phoenix Offshore Platform in the North Sea in day Visual Meteorological Conditions (VMC) was in the cruise 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 close to a ship and, with the Emergency Flotation System functioning normally. All 19 occupants evacuated into the two life rafts and were soon rescued with no injuries sustained.
An Investigation was commenced by the UK AAIB. It was soon established that the sequence of events was almost exactly the same as one which had occurred to another EC225 LP five months earlier also operating offshore out of Aberdeen, also followed by a successful controlled ditching and also under investigation by the AAIB. The Investigation is continuing into this second event and it was announced on 29 November 2012 that it has been combined with one into the earlier similar event because of the essential similar airworthiness issues raised.
An initial Special Bulletin was published on this event and thereafter further Special Bulletins have dealt with progress in both investigations:
- S6/2012, published on 24 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
Special Bulletin S6/2012 noted that the EASA AD action which followed the earlier event and had required specific action to monitor two gearbox maintenance alerts had been for only a limited range of Part Numbers for the failed shaft which did not include the one fitted to the helicopter involved in this second event.
The issue of Special Bulletin S2/2013 on 18 March 2013 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 was known to be fitted to several other aircraft types not addressed by actions taken in respect of the EC225, two more Safety Recommendations were 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.