A fleet of Royal Navy helicopters has been grounded while safety checks are carried out on "possibly thousands" of individual components.
The submarine hunting Merlin Mark I, which while on dry land are based at RNAS Culdrose near Helston in Cornwall, will only undertake urgent operational missions until every aircraft is cleared for flight.
A Ministry of Defence (MoD) spokesman said safety was paramount.
"Flight safety is of utmost importance and it is entirely appropriate that commanders have taken the practical decision to check the aircraft in this way, as part of the assurance process," he said.
The Merlins were grounded on November 9 after an issue arose with the electronic system for managing and recording maintenance activity on each aircraft. It is understood that some of the data held on computer did not tally with individual components.
This in turn raised the prospect that more than one record might be incorrect, forcing commanders to ground the entire fleet of more than 30 Mark I Merlins – as well Mark III Merlins flown by the RAF.
A former Royal Navy officer told the Western Morning News that this could potentially mean "possibly thousands" of components needed to be double-checked.
"It's a huge job. They will have to take everything apart from every Merlin, check it, log it and then put it back," said the former officer, who asked not to be named.
The MoD was asked to clarify the extent of the scrutiny and how the problem was thought to have occurred.
The response to both questions was: "An investigation is under way and it would be inappropriate to comment at this stage."
The spokesman said Merlins deployed on operational missions would continue to operate, adding: "UK Merlins are now undertaking gradual return to flying, while checks continue."
Beth Torvell, of the Navy Campaign, an independent group which speaks out for the service, said: "I understand that once they discovered anomalies in the paperwork, the Merlin fleet was grounded while they work through the process of identifying which parts of the helicopters are affected.
"Because of the variety of environments and the intensity of Fleet Air Arm flying, they take this very seriously. If a part in your helicopter breaks mid-deployment to the South Atlantic that can be a life-or-death issue."
In August, dozens of Sea King helicopters in the Westcountry were grounded while a potential technical fault was investigated.