A spokeswoman for the Lockheed Martin-owned firm confirmed the alert was for fleet-wide maintenance action, which includes around 10 helicopters in Australia.

 

The UK Air Accidents Investigation Branch has just issued an interim report on the December 28 incident on the West Franklin wellhead platform that led to the fleet being temporarily pulled from service until inspections could be carried out.

 

The report was compiled since the regulator was alerted to the incident on January 5.

 

An S-92 helicopter was on the second sector of a four-sector rotation from Aberdeen to the Elgin-Franklin field in the North Sea on December 28. 

 

After an uneventful flight to the Elgin facility the pilot took off but the S-92 yawed unexpectedly to the right through 45 degrees.

 

The aircraft was swiftly bought under control, and the crew determined the cause was most likely the impact of turbulence or wind effects created by the platform structures which, anecdotally, is not uncommon for that helideck.

 

After taking off again, the helicopter made the three nautical mile trip towards the West Franklin wellhead platform, however about four feet above the deck the S-92 yawed rapidly to the right and rolled to the left, at which point the left main landing gear contacted the helideck, and the S-92 stared spinning on its wheels.

 

There were no injuries for the nine passengers or two crew. 

 

The helicopter was subsequently craned from the helideck onto a ship and recovered to Aberdeen.

 

On inspection it was immediately apparent that the tail rotor servo piston was damaged and the tail rotor pitch change shaft was in a severely distressed condition.

 

There were signs of severe overheating with extreme wear.

 

Work suggested the failure of the bearing took place in just 4.5 hours.

 

There have been two previous events with the same model, the first being in 2007, where a degradation of the TRPCS bearing occurred, leading to reduced tail rotor control in flight, but it is not clear if that minor incident is related.

 

The operator of the helicopter has already made a number of changes, including a maximum five-hourly review of safety data from the Health and Usage Monitoring System.

 

Sikorsky's own alert emphasised the use of a ground tool that will immediately detect degradation. 

 

It issued an Alert Service Bulletin requiring the mechanism be inspected on January 10. 

 

"We greatly appreciate the UK Air Accidents Investigation Branch's work to understand this issue, and we will continue to support the ongoing investigation by the AAIB along with the NTSB, as well as our customer, into the root cause of the suspected TRPCS Bearing failure," Sikorsky said in a statement.

 

It said operators were reporting completion of the required inspections, and it expected the reviews would be completed by the weekend.