'We are amazed that the results of the test flights done by (main carrier) Lufthansa and Air Berlin have not had any bearing on the decision-making of the air safety authorities,' Air Berlin Chief Executive Joachim Hunold said in a statement.
Air Berlin is Germany's second biggest airline after Lufthansa.
A spokesman for Britain's weather service, the Met Office, which runs the Volcanic Ash Advisory Centre in London, said its forecasts were being confirmed by observations from the ground and satellite.
He said radar sightings of the airborne ash, which is not visible to the naked eye, were 'correlating very well with what those predictions were'.
'There are going to be clear areas, but those clear areas are not going to stay in the same place,' he said. 'Just because they (Air Berlin) had a clear spot doesn't mean it's not there.'
European airspace has been restricted for up to four days, costing airlines hundreds of millions of euros, after a volcano erupted in Iceland.
Air Berlin said in a statement it carried out three test flights at low altitude and was offering to do more. It said it was lacking guidance from the federal transport ministry and called for better cooperation between air carriers and the authorities.
The first plane tested by Lufthansa flew at 3 km, the others at up to 8 km. Air Berlin did not comment on the exact height of the test flights.
'We offer -- as does Lufthansa -- to carry out more such flights to gain valid insights.'
But German Transport Minister Peter Ramsauer told Bild daily that measurements taken on Sunday near Munich, in southern Germany, showed there was still volcanic ash in the air. He said the measurements were made with modern laser technology.
A spokesman for Britain's Civil Aviation Authority questioned the worth of commercial airliner test flights.
'You can tell when you land the aircraft whether you have done any damage to it. Whether that is a scientific test flight or not, would be for someone else to say,' he said.
He contrasted them with observational flights conducted by the Met Office over recent days in a Dornier 228 twin turboprop.
'(They are) not quite the same as a proper test flight with data, recording and special sampling on board the aircraft.'
Lufthansa carried out test flights by 10 aircraft on Saturday and said post-flight inspections showed no impact on the planes, while Dutch airline KLM also said tests by aircraft had revealed no engine damage or other problems.
Air Berlin extended its flight cancellations until at least 2400 GMT Sunday.
Hunold also was quoted in a newspaper as complaining about the air travel restrictions.
'The closure of the air space happened purely because of the data of a computer simulation at the Volcanic Ash Advisory Centre in London,' he told the mass circulation Bild am Sonntag (BamS) paper.
Referring to the same point, a spokesman for Lufthansa said it was 'scandalous' that the closure was triggered by only one source as it was causing massive revenue losses.
'We reserve the right to ask the question who is liable here, who will pay for the (financial) damage,' he told Reuters.
He put the losses from the grounded fleet at 25 million euros a day at least.
DEFENDS BAN
Ramsauer defended the flight ban, saying he was sticking to strict international rules.
'To do anything else would be irresponsible,' Ramsauer told Bild daily, adding his priority was passenger safety.
Ramsauer said the ban could last several more days, depending on the weather conditions.
He said he would speak to other EU transport ministers on Monday evening about long-term measures.
German Economy Minister Rainer Bruederle expressed concern about the effect of the chaos on companies and the economy.
'The ash cloud presents special challenges for the German economy,' he said in a statement.
(Reporting by Vera Eckert and Martin Zwiebelberg and Madeline Chambers in Berlin and Tim Castle in London; Editing by Michael Roddy) Keywords: AIRBERLIN/ (vera.eckert@reuters.com; +49 69 7565 1270; Reuters Messaging: vera.eckert.reuters.com@reuters.net) COPYRIGHT Copyright Thomson Reuters 2010. All rights reserved. The copying, republication or redistribution of Reuters News Content, including by framing or similar means, is expressly prohibited without the prior written consent of Thomson Reuters.
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