Local authorities are still to approve plans for the fire safety systems in the passages connecting the airport's terminal and underground train station, Berlin's Tagesspiegel newspaper reported on Wednesday.
Officials are not satisfied with the simulations offered by planners of what would happen in the event of a fire in the tunnels while trains were passing through the station.
Without the construction permit for the smoke extractors, there is no chance of getting the airport ready for action by December 2017 – already more than six years after it was supposed to open.
Airport boss Karsten Mühlenfeld maintained in an interview with Tagesspiegel that a 2017 opening could still be possible if he receives the permits as hoped by July or August this year.
But local head of building regulation Stephan Loge confirmed to Berlin's RBB radio on Wednesday that the delay in issuing the permits would make it “inevitable” that the airport could not open until 2018.
Technical failure and corruption
The Berlin-Brandenburg Willy Brandt airport project – named after the legendary Social Democratic Chancellor and long-time mayor of the German capital – has been floundering since missing its original opening date of 2011.
A second planned opening date in 2011 was pushed back while the third, in 2012, was cancelled just 10 days in advance after plane tickets had already been issued.
The budget for the stricken airport has ballooned from €2.83 billion to more than €5 billion, with further costs in keeping the existing Tegel and Schönefeld airports open past their planned closure dates.
And planners have suggested that another terminal may have to be built, as the structure as-is may not be able to handle the number of passengers expected.
After the resignation of project chief Hartmut Mehdorn in 2014 and the installation of former Rolls-Royce executive Mühlenheld as the new boss, there had been hope that the mega-project would gather momentum again.
A number of former managers at the airport have also been caught up in corruption allegations, with the former technical director convicted of corruption and fraud in 2014.
Most recently, the project's PR director was fired for admitting to a trade magazine that the entire saga had been a "shit show" and calling on managers to "take responsibility".
"No politician or airport director, no person who is not addicted to pills, would give you definitive assurances about this airport," he told PR Magazine when asked about the 2017 opening date.
Note: This article has been updated to more clearly state that the airport was originally scheduled to open in 2011.