After a meeting of the airport's supervisory board, officials of the airport, owned by the states of Brandenburg and Berlin as well as the federal state, said a decision was now due on September 14 on whether it would open on March 17, 2013.

"At the latest at the next board meeting in mid-September, we will have clarity and will be able to say whether the opening date stands or not," Horst Amann, who took over as the airport's chief operating officer at the start of the month, told reporters.

Amann and his team were still trying to figure out how much more work needed to be done to get the airport running.

Originally, Berlin-Brandenburg Airport was due to open in 2011 but the opening has been delayed twice already. In May, the scheduled opening for June 3 was scrapped due to problems with fire safety systems.

More than 20 years since German reunification, the capital is still making do with two small airports that date back to the Cold war era.

The delays have been a headache for Germany's second-biggest airline Air Berlin (AB1.DE) in particular, which plans to use the new airport as a hub for more lucrative intercontinental flights.

It also increases the pressure on managers at the airport operation and Berlin mayor Klaus Wowereit, a Social Democrat who had made the airport his flagship project and who sits on its board.

"(Wowereit) is making the city look more and more ridiculous in international eyes," said Rainer Bruederle, a senior member of the Free Democrats FDP.L, who share power in Chancellor Angela Merkel's centre-right coalition.

The delays will likely make the airport, to be named after West German Cold War chancellor Willy Brandt, more expensive than the roughly 2.5 billion euros it was projected to cost,

But deputy transport minister Rainer Bomba, who represents the ministry on the airport's board, said the government remained committed to the project.

Opening the airport is of vital importance for loss-making Air Berlin. The company wants to use it as a hub for more intercontinental routes, which are more profitable than flights within Europe but impossible to run at the small Tegel airport.

"We need Berlin-Brandenburg because this situation is not sustainable in the long term," Air Berlin chief executive Hartmut Mehdorn said on Wednesday.

Lufthansa, whose home hub is in Frankfurt but also has plans to expand its services from Berlin, has said the most important thing is that any new date is reliable.

The new airport will replace Tegel in western Berlin and Schoenefeld in the former Communist eastern part of the city. It will be Germany's third biggest airport after Frankfurt and Munich.

UK-based easyjet (EZJ.L) will also run out of the new airport, which aims to attract up to 27 million passengers a year. (Reporting by Oliver Keck, Annika Breidthardt, Hans-Edzard Busemann and Victoria Bryan; Editing by Alison Williams)

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