Helicopter flights over the North Sea were recalled after two aircraft reported being covered with volcanic ash.
The two Bond-operated aircraft were flying about 70 miles off Aberdeen.
The pilots reported ash on the windscreens after flying through a rain cloud on Tuesday night. There was no damage and no ash was found in engines.
The later decision to close airspace over parts of the North Sea led to the cancellation of helicopter flights.
Bond said it had cancelled all offshore flights, while Bristow cancelled all services from Scatsta in Shetland. CHC has also stopped some flights.
Hundreds of offshore workers were left stranded in the wake of the Iceland volcano ash flights disruption.