The cause of the helicopter crash which resulted in the death of 13 oil workers – including one from Scotland – in Norway in 2016 was caused by a catastrophic mechanical failure.
- According to Norway’s air accident investigation agency, one of the internal ring gears in the main turbine gear-box on the CHC Helicopter flight developed cracks and splintered under pressure – sending metal chards careening around the gear-box and causing it to fail catastrophically.
- But the investigators said the accident was not caused by either crew failure or any failure in maintenance and inspection procedures.
The report concluded: “The main rotor suddenly detached from the helicopter without warnings. Shortly after, the helicopter impacted a small island near Turøy, northwest of Bergen.
“The accident was a result of a fatigue fracture in a second stage planet gear in the epicyclic module of the main rotor gearbox. Cracks initiated from a micro-pit at the surface and developed subsurface to a catastrophic failure without being detected.
“There are no connections between the crew handling and the accident. The AIBN has also excluded material unconformity and mechanical failure, as well as maintenance actions by the helicopter operator.
The accident happened on 29 April 2016 after the main rotor suddenly detached from an Airbus Helicopters EC 225 LP Super Puma, operated by CHC Helicopters. The helicopter was ferrying oil workers for Statoil ASA and was en route from the Gullfaks B platform in the North Sea to Bergen Airport Flesland.
The helicopter had just descended from 3,000 ft and had been established in cruise at 140 kt at 2,000 ft for about one minute. The flight was normal and the crew received no warnings before the main rotor separated from the helicopter.
The helicopter impacted a small island near Turøy, northwest of Bergen. Wreckage parts were spread over a large area of about 180,000 m2 both at land and in the sea. The main rotor fell about 550 meters north of the crash site. The impact forces destroyed the helicopter, before most of the wreckage continued into the sea. Fuel from the helicopter ignited and caused a fire onshore.
All 13 persons on board perished, including 41 year old oil worker Iain Stuart from Laurencekirk in Aberdeenshire. He worked for the oil field services company Halliburton.
The Norwegian accident report advises a number of process improvements for Super Puma helicopter operators and manufacturers.
The design of the EC 225 LP satisfied the requirements in place at the time of certification in 2004. However, the AIBN has found weaknesses in the current European Aviation Safety Agency (EASA) Certification Specifications for Large Rotorcraft (CS-29).
The accident has clear similarities to an Airbus Helicopters AS 332 L2 Super Puma accident off the coast of Scotland in 2009 (G-REDL). This accident was also identified to be the result of fatigue fracture in a second stage planet gear.
However the post-investigation actions were not sufficient to prevent another main rotor loss (as in this case)
The earlier fatal crash of an AS332 L2 off the coast of Scotland in 2009 killed 16 people. In that aircraft (G-REDL), the main rotor also detached following what was later discovered to be a fatigue fracture in a second stage planet gear.
Both Norway and Britain suspended commercial flights of the type of helicopter involved in the crash, an Airbus Helicopters H225 Super Puma, a workhorse of the offshore oil industry.
Watch Norway’s air accident agency video re-construction and crash-scene footage and investigation here:
Oil workers and Scots families demand global ban on Super Puma helicopter after 13 people die in Norway crash
12 Jul 2018