Sikorsky has issued an Alert Service Bulletin (ASB) calling for inspection of S-92 helicopters used to carry workers to and from offshore oil platforms. This follows an incident on 28th December in which an S-92 operated by CHC made a hard landing on an oil and gas installation in the Elgin-Franklin Offshore Field in the North Sea following loss of tail rotor effectiveness.
According to a report by the UK Air Accidents Investigation Branch (AAIB), the technical investigation revealed that the tail rotor pitch change shaft (TRPCS) double row angular contact bearing was in a severely distressed condition, leading ultimately to a total loss of control of the tail rotor.
This was the third event over the past 10 years involving a degradation of the TRPCS bearing on the S-92. Underlying causes had been identified and a number of safety measures introduced. Investigators are seeking to understand whether the recent incident is the result of a new root cause, or a previously unidentified failure mode.
The ASB issued by the manufacturer on 10 January 2017 called for a one-time inspection of the TRPCS and bearing assembly “for ratcheting, binding, or rough turning”. Operators are also required to review data from the helicopter’s health usage and monitoring system (HUMS).
On 13th January, the FAA issued an Emergency Airworthiness Directive (AD) requiring a one-time visual inspection and a repetitive borescope inspection of the TRPCS assembly bearing.
This latest incident comes in the aftermath of an accident in April 2016 involving another oil and gas workhorse, the Eurocopter H225, in which 2 crew and 11 passengers lost their lives. That flight was also operated by CHC. Though the European Aviation Safety Agency (EASA) cleared the helicopter — and the AS332 L2 variant — to resume flying in October, authorities in the UK and Norway still have flight bans in place.
CHC filed for bankruptcy protection in May 2016.