At least one offshore helicopter company has begun passenger flights to oil and gas installations, nine days after an AS332 L2 Super Puma crashed off Shetland with the loss of four lives.
Bristow said it resumed operations using the Eurocopter-built Super Puma AS332 L on Monday after an earlier voluntary suspension was lifted by the oil industry's Helicopter Safety Steering Group (HSSG). The aircraft is an older version of the L2 that crashed.
It is understood many of the Super Puma models, which account for 70% of the North Sea fleet, are undergoing pilot-only operations in readiness for taking passengers again.
The move came after the Civil Aviation Authority (CAA), which regulates aviation in the UK, issued a statement on Friday saying it did not believe the accident was caused by an airworthiness or technical problem, based on the information available.
However, the Air Accidents Investigation Branch (AAIB), which is leading the probe into the crash, has said it is unable to ascertain why the CAA arrived at that verdict.
The AAIB, which has in the past has given early indications of the causes of crashes, insisted after its initial investigations it was too early to draw conclusions on what caused the Super Puma AS332 L2 to crash.
Now Unite regional industrial officer John Taylor has said the 13 AS332 L2s serving the UK oil and gas industry should remain grounded until there is a clear indication about what caused the crash.
Mr Taylor said: "All I know is the helicopter came down, we don't know what the reasons are, and until we do, we should keep them grounded."
Chancellor George Osborne joined oil and gas industry representatives in Aberdeen yesterday in a minute's silence for the victims of last week's helicopter crash before he flew on a Super Puma to the Montrose platform, one of the oldest in the North Sea.
The CAA said it stood by support for the lifting of the ban on Super Puma passenger flights, including the use of the L2.
A CAA spokesman said: "With the available information as it stands, there is nothing that makes us think it would be unsafe for the aircraft to operate. We wouldn't let it operate if we thought it would be unsafe."
The AAIB said it was still too early to rule out any technical problem with the AS332 L2 that crashed.