Airlines are searching for safe flight paths through the cloud of volcanic ash that has grounded most aircraft for the past four days.
Dutch airline KLM and the German airline Lufthansa have already carried out test flights in their countries' airspace, adding to pressure on air traffic controllers to restore services.
KLM said that a Boeing 737 reached up to 12,500 metres, the maximum altitude at which the aircraft is certified to fly, in Dutch airspace without it suffering any damage. The Dutch airline, a subsidiary of Air France, said that it wanted to resume passenger flights in Europe as soon as possible, adding that it planned to return seven jets without passengers to Amsterdam from Dusseldorf.
Peter Hartman, chief executive of KLM, who was on board the test flight, said: "We observed no irregularities either during the flight or during the initial inspection on the ground.
"We hope to receive permission as soon as possible to start up our operation and to transport our passengers to their destinations."
Mr Hartman was quoted as saying that he had begged Eurocontrol, the European air navigation safety agency, to consider lifting the flight ban but the agency has so far refused to discuss the matter.
Lufthansa and Air Berlin said that the ban on flights was ordered without proper testing and that their aircraft showed no signs of damage after the test flights.
British Transport Secretary Lord Adonis said he would hold a video conference with European transport ministers today to examine the results of test flights across northern Europe.
It would be "hugely disruptive" if the flight ban was to continue for days on end, he said.
"But as we get more observation data, that is being fed in to the European regulators and, as I say, there will be meetings taking place over the next day to see whether it's possible to find a way through, despite the fact that we still have the ash cloud present and will do for several more days."
He said he could not give details of where British test flights were taking place but one such test plane had already completed its mission yesterday.
"Those results are being analysed at the moment and we will take full account of those results when we feed all of our data, as the Dutch and the Germans and the French are feeding their data, into the European regulators," he said.
Pressed on whether all ash had to be out of the sky for a flight to be safe, Lord Adonis replied: "This is precisely the issue that safety regulators are examining with the aircraft manufacturers at the moment, whether the no-ash, no-fly -- if there's any ash at all, there can be no flying -- rule is appropriate to the ongoing situation, or whether there is any scope for updating that rule." (© The Times, London)