Restrictions on flights in and out of the UK have been extended until at least 7am on Sunday.
The move comes as the ash cloud created by an erupting volcano in Iceland is "moving around and changing shape", according to air traffic control company Nats.
If it "moves sufficiently", some domestic flights may be able to take off from Scotland and Northern Ireland.
The cloud has prevented many flights from entering or leaving the UK since noon on Thursday - at a huge cost to the industry. Experts estimate the cost to British and Irish airlines could total nearly £28m per day.
British Airways have cancelled all short-haul flights into and out of Britain on Sunday.
A spokeswoman for the airline said the cancellation covered all flights to and from European destinations as well as domestic services. A decision on long-haul flights would be made later.
