Twenty-five helicopters that service the offshore oil and gas industry have been grounded after urgent safety checks were ordered on two models of the Super Puma aircraft.
It comes after the Air Accidents Investigation Branch (AAIB) ordered further “urgent” inspections on gearboxes following the latest report into the North Sea crash in which 16 people died.
Operators were given a week to carry out safety checks or have their Super Pumas grounded indefinitely.
The order applies to two models of the helicopter – the AS332L2, which was involved in the most recent crash on April 1, and the EC225LP, which ditched in the North Sea 120 miles east of Aberdeen in February in which all 18 on board survived.
Both models have been temporarily grounded by the industry body Oil and Gas UK. Twenty five helicopters in the UK offshore fleet will be affected.
Its statement said: “Oil and gas companies operating in the UK offshore are temporarily refraining from flying the two models of Super Puma helicopter subject to the latest recommendation issued by the UK Air Accidents Investigation Branch.
“This will apply to all passenger flights over the weekend.”
The AAIB alert has gone out to all European Super Puma operators, in 31 countries, asking them to carry out the checks on helicopter gearboxes by Friday or face having the models grounded.
An initial AAIB report published by investigators said a “catastrophic failure” of its main gearbox was to blame.
It also revealed that a loose metal particle was found on a magnetic chip detector in a section of the gearbox seven days before the crash.
The appearance of such debris is seen as an early warning of possible gearbox failure.
The second initial report released yesterday stated: “However, during the period between the discovery of the chip and the accident, no signs of an incipient gearbox failure were detected.”
The AAIB added it was recommending the new checks “as a matter of urgency to ensure the continued airworthiness of the main rotor gearbox”.
The recommendation, which was made mandatory by European Aviation Safety Agency following the AAIB report, effectively requires operators to strip the section and start again.
Ex-RAF pilot and Flight International magazine’s operations and safety editor David Learmount said investigators issued the warning because they were still no closer to discovering the cause of the initial fault.
He said the new recommendation would be psychologically “very unnerving” for those flying in Super Pumas.
He said: “They know what the failure did, and what the results were, but they still don’t know why it failed in the first place.
“They’re asking them to take it apart and look through everything -take it to bits and look at everything as if you have not looked at it before.
“They’re looking for something which is really scary – a sudden fault which gives no warning.
“The main gearbox and the rotor are the two components which, if they fail catastrophically during flight, there is no back-up for them. There is only one main rotor and one main gearbox.”
Investigators said yesterday that while they still do not know what caused the initial failure, they now understand more about its sequence.
Yesterday’s report revealed that the gearbox casing ruptured, which caused the main rotor to separate from the helicopter.
The gearbox is one of the load-bearing structures that keeps the rotor connected to the fuselage, so when it broke, it sent the helicopter plummeting more than 2,000ft into the sea below.
A statement issued by the AAIB said: “The sequence of failure is now better understood but further work is required to determine the initiating event.
“The painstaking work continues as the final failure of the gearbox involved the transport of metal debris through the meshing gears and bearings, absorbing energy from the engines and rotor assembly, leading to the gearbox bursting.
“This has resulted in a large amount of secondary damage to all gearbox components potentially masking the initial failure.”
Representatives from the oil and gas companies, together with the helicopter operators Bond, Bristow and CHC Scotia, will meet tomorrow afternoon to decide what further action needs to be taken.
Jake Molloy, regional organiser of the RMT union, said report would cause offshore workers more concern as additional gearbox checks were already in place.
“We feel it would be appropriate in the absence of a definitive finding into the cause of the crash to ground the model,” he said.
The 14 passengers and two crew were returning from BP’s Miller platform when the helicopter crashed 11 miles north-east of Peterhead.
On Wednesday, the Duke and Duchess of Rothesay, Prime Minister Gordon Brown and First Minister Alex Salmond were among those attending a memorial service for the dead men.
A service was held on the platform the following day.
Last night, the Crown Office and Procurator Fiscal Service confirmed that the bodies of the remaining two UK victims of the crash could be returned to their families.
Arrangements are also being made for the return of the body of Mihails Zuravskis to his family in Latvia.
The bodies of the 13 other men were returned to their families earlier this week.