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Norwegian Investigators Identify Possible Maintenance Issue

Norwegian Investigation Links Sikorsky S-92 Engine Failure to Maintenance Concerns
Norwegian investigators have identified a probable maintenance-related cause behind the in-flight engine failure of a Sikorsky S-92 helicopter operated by Bristow Norway. The incident occurred shortly after the aircraft departed the Linus mobile drilling platform on 5 June 2023. Carrying two pilots and 14 passengers, the helicopter had ascended to an altitude between 3,000 and 4,000 feet when the crew reported hearing a “loud bang,” according to the final report issued by the Norwegian Safety Investigation Authority (NSIA).
Details of the Incident and Technical Findings
Flight instruments indicated that the left-hand engine had ceased functioning, and despite attempts, the crew was unable to restart it. Judging a return to the platform unsafe, the pilots opted to continue to Stavanger Sola airport on a single engine, escorted by a rescue helicopter. Subsequent technical examination revealed a critical failure within the GE Aerospace CT7-8A turboshaft engine. Specifically, the joint connecting the centrifugal impeller to the compressor rotor rear shaft, which is secured by 12 T-head bolts, had become disconnected. All twelve bolts exhibited fatigue fractures, leading to the uncommanded engine shutdown.
Laboratory analysis conducted by Qinetiq in the United Kingdom confirmed fatigue on each bolt but was unable to determine a definitive root cause. The NSIA noted that metallurgical examinations could not establish whether the bolts had been installed correctly or torqued according to specifications. Notably, no similar failures involving the CT7-8A engine were found in GE’s records.
The engine in question had undergone repair at ITP Aero’s Albacete facility in 2020, was released to service in June 2022, and installed on the helicopter in November 2022. It had accumulated 894 flight hours before the failure occurred.
Maintenance Procedures and Industry Implications
While the NSIA deemed a material defect unlikely, the investigation highlighted minor discrepancies in ITP Aero’s maintenance procedures. The report outlined several potential scenarios, including incorrect tightening torque during bolt installation or improper matching of joint components. The assembly process was described as “critical and complex,” underscoring the heightened risk of human error.
In response, ITP Aero has implemented safety-enhancing measures to address the identified concerns. The NSIA recommended that GE revise its workshop manual to include clearer instructions and additional procedural steps aimed at reducing assembly errors.
The findings carry significant implications for the offshore sector, where helicopter transport plays a crucial role. The investigation may prompt increased regulatory scrutiny and pressure on maintenance standards, extending beyond oil and gas platforms to related industries such as offshore wind energy. Market reactions could include temporary declines in the stock prices of companies involved in offshore operations, as investors reassess risks associated with maintenance failures. Concurrently, competitors may intensify efforts to demonstrate the safety and reliability of their projects, potentially driving innovation and heightened competition across the sector.

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