The charity's helicopters have traditionally been leased
Great North Air Ambulance cover is set to resume following the grounding of its fleet of helicopters last week.
Two of the charity's three aircraft, based at Otterburn, Northumberland, and Langwathby, Cumbria, were taken out of service because of mechanical problems.
The lease on the third helicopter, near Darlington, ran out on Thursday and the charity is yet to find a replacement.
A spokeswoman said one of the aircraft had now been repaired and cover was expected to be restored on Monday.
The organisation is attempting to buy a new helicopter for its Durham Tees Valley base, as it moves away from a policy of leasing its aircraft.
Sarah Booth, of the Great North Air Ambulance, said it had hoped to extend the lease as the search continued for a replacement but the air ambulance had already been sold on by its owners.
She said: "Ideally we always want to work with three helicopters but we will have one up and running today.
"Hopefully we will find out this week when we will have the second one back and we are looking at (buying) a third aircraft over in Stockholm."
The charity plans to have three larger helicopters in service next year, which it says will provide an improved service.
It says buying the aircraft will prove more cost effective than leasing arrangements.
The Yorkshire Air Ambulance and the North West Air Ambulance charities also provide cover for Cumbria and North Yorkshire.