Nighthawk From UK - Scotland, joined Sep 2001, 4989 posts, RR: 38 Posted (4 years 1 month 1 week 5 days 7 hours ago) and read 1890 times:
The preliminary report into last weeks fatal helicopter crash in the north sea has been released:
Quote:
In common with similar helicopters operating in the North Sea, the helicopter was additionally
equipped with a Health and Usage Monitoring System (HUMS), which comprises a system of
sensors around the engines, airframe and drive train. Recorded information includes vibration levels
together with gearbox chip detection from a series of magnetic plugs. The data accumulated during
helicopter operations is transferred, usually on a daily basis, to the operator’s ground-based computer
system. The data is then subjected to mathematical processes that establish basic signatures and
enable trends to be monitored for individual components. The HUMS data for the day’s operation,
including the accident flight, has also been recovered. As the result of the discovery of a particle on
the main rotor gearbox epicyclic module magnetic chip detector on 25 March a daily inspection of
the epicyclic gearbox magnetic chip detector was initiated. Also, the HUMS data was downloaded
and analysed each time the helicopter returned to its base at Aberdeen for the next 25 flying hours.
No further abnormalities were identified during this period.
Examination of the wreckage indicates that the accident occurred following a catastrophic failure of
the main rotor gearbox (MGB). This resulted in the detachment of the main rotor head from the
helicopter and was rapidly followed by main rotor blade strikes on the pylon and tail boom, which
became severed from the fuselage. It is apparent that there was also a rupture in the right hand (No2)
engine casing, in the plane of the second stage power turbine. This is currently believed to be a
secondary feature. Investigations are continuing in order to understand completely the accident
sequence.
The investigation has so far revealed that the MGB had suffered from a major failure within the
epicyclic module. This is supported by HUMS data; however, this is not yet fully understood. The
examination of the MGB is continuing in conjunction with detailed analysis of the HUMS and other
recorded information.
As a result of the crash the following safety directives have been issued:
Quote:
Safety Recommendation 2009-048
It is Recommended that Eurocopter issue an Alert Service Bulletin to require all operators of
AS332L2 helicopters to implement a regime of additional inspections and enhanced monitoring to
ensure the continued airworthiness of the main rotor gearbox epicyclic module.
Safety Recommendation 2009-049
It is Recommended that the European Aviation Safety Agency (EASA) evaluate the efficacy of the
Eurocopter programme of additional inspections and enhanced monitoring and, when satisfied, make
the Eurocopter Alert Service Bulletin mandatory by issuing an Airworthiness Directive with
immediate effect.
Safety Recommendation 2009-050
It is Recommended that Eurocopter improve the gearbox monitoring and warning systems on the
AS332L2 helicopter so as to identify degradation and provide adequate alerts.
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From UK - Scotland, joined Sep 2001, 4989 posts, 
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