Noise insulation and the large terminal building were driving costs beyond the expected €4.3bn, Bretschneider told German broadcaster ZDF, and additional levies were payable for every month the airport remains closed.
“I still believe the airport will be able to cover its costs, but not as swiftly as thought,” he said.
The fate of the airport has dented Germany’s reputation for efficiency.
Already 20 years in the planning when construction began in 2006, the airport was then set to open in 2011.
That was pushed back to June 2012, then to March 2013, then to October 2013 and now to some point after 2014.