All coastguard rescue helicopters in Scotland have been grounded because of safety fears.
Air safety officials have ordered replacement parts be fitted to Sikorsky S-92 aircraft following a crash off Newfoundland last week.
Seventeen people died when the aircraft came down in the Atlantic on 12 March.
The UK coastguard agency operates four S-92s based on Shetland and Lewis. The RAF and Royal Navy will continue to provide emergency cover.
A preliminary investigation into the crash in Canada suggested a gearbox mounting stud had failed.
A Maritime and Coastguard Agency (MCA) spokesman said replacement parts should arrive on the islands "within a day or so" but the helicopters could be out of action for several days while they are fitted.
He said: "We have a responsibility to our crews. We have to ensure that the helicopters are safe.
"The MCA are now working closely with the Ministry of Defence to provide cover for the islands from Lossiemouth and Prestwick."
In the meantime, RAF and Royal Navy helicopters would provide emergency cover, he said.
Coastguard helicopters in England are of a different type and are unaffected.