The search has been narrowed to a 100 metre by 80 metre section of the ocean around Blackrock lighthouse, around 13km offshore from Blacksod, where the aircraft was intended to land to refuel moments before it vanished.
It is hoped if Sunday's tightly-managed operation to try and locate the helicopter is successful, then a "bigger window" will be available on Monday during which divers or remotely operated underwater vehicles will be deployed to the wreckage.
Mayo search operation stalled by poor weather