Puma crash probe orders gear review

Published on Thursday 16 July 2009 22:02

AN URGENT review of engine gears in Super Puma helicopters was ordered yesterday by officials investigating the North Sea crash which killed 16 men.

The way in which checks are carried out to identify debris found in the aircraft's gearboxes should also be re-examined, the Department for Transport's Air Accidents Investigation Branch (AAIB) reported.

The crash on 1 April happened 11 miles north-east of Peterhead as the Eurocopter AS332L2 Super Puma was returning to Aberdeen from BP's Miller platform.

The ongoing investigation has already established it was caused by the "catastrophic failure" of the helicopter's gearbox, within which metallic debris had been found.

A third interim report, published yesterday, showed sensors had recorded four metal slivers in the three minutes before the pilots sent a mayday. The pilots were not alerted to this because such information has to be manually downloaded while the aircraft is being serviced.

The AAIB said the failed gearbox could have been removed from service before the crash if not for the "inappropriate diagnosis" of a previously detected debris particle.

The particle was found, one week before the crash, on the gearbox magnetic chip detector, which is used to attract any bits of metal which can get into the system. The appearance of such debris is seen as an early warning of a possible gearbox failure.

However, at the time, those who carried out the maintenance for helicopter operator Bond concluded the particle was of a type that did not require further investigation.

The magnetic chip detector in the gearbox was then inspected daily up until 31 March, the day before the accident, and no further abnormalities were found.

The AAIB report stated: "Had a different diagnosis of the chip type been made on March 25, it is possible that the main rotor gearbox (MRG) would have been removed from service for further investigation."

Investigators found evidence of damage caused by debris on all the gear teeth, consistent with them running in an abnormal condition before the main rotor head separated from the aircraft. They recovered 66 per cent of the gear component that failed, and it had five conjoined cracks.

The AAIB called on the European Aviation Safety Agency (EASA) and Eurocopter to urgently review the design, operational life and inspection processes of the gears. The EASA said significant work had already been carried out on the issues.

A spokesman for Bond said its inspections had followed the manufacturer's agreed procedures, and follow-up checks found no abnormalities.

COUNTDOWN TO DISASTER

THE doomed helicopter flight's timeline:

12:03pm: 1 April: Super Puma takes off from BP's Miller platform with 14 oil workers and two crew on board.

12:51: Metallic sliver is detected by gearbox magnetic chip detector.

12:52: Two more slivers are detected.

12:53: A fourth sliver is detected.

12:54:01: Routine call from co-pilot that helicopter is serviceable and arrival in Aberdeen expected at 1:14pm.

12:54:13: Brief mayday call is made by one of the pilots.

12:54:18: Main rotor gearbox low pressure warning is recorded.

12:54:23: Combined cockpit voice and flight data recorder ceases recording.

12:55: Helicopter crashes.