The UK is enduring a fourth day as a virtual no-fly zone, as the travel chaos caused by volcanic ash drifting from Iceland shows no sign of ending.Flight restrictions have been extended until at least 7pm and forecasters say the ash cloud could remain over the UK for several more days.
BBC business editor Robert Peston said the disruption risked becoming a "major business and economic disaster".
He said a number of European airlines were facing financial difficulties.
Our correspondent said: "If [the disruption] goes on many days longer, a number of European airlines will run into financial difficulties and may need bailing out by governments - or so I am told by senior airline figures."
On Friday, the International Air Transport Association (IATA) warned airlines would lose at least $200m (£130m) per day in revenues during the disruption.
Meanwhile, Dutch airline KLM and German airline Lufthansa have carried out test flights in their countries' airspace to see if it is safe for planes to fly.
KLM said its aircraft had been able to fly at its normal operating altitude of 13km (8 miles) over Dutch skies and no problems had been reported. The plane's engines were being inspected for possible damage, with a view to getting permission from the aviation authorities to start up operations again.
The disruption has affected hundreds of thousands of travellers since Wednesday, when the Eyjafjallajoekull volcano began erupting.
Among those affected were British wedding guests who had to watch on an internet connection as a bride and groom stranded in Dubai took their vows.
Link to live webcam of the volcano
In the shadow of the volcano
