Germany's second-biggest airline Air Berlin files for insolvency on Tuesday after its biggest investor announced to withdraw support.

As the major shareholder Abu Dhabi-based Etihad Airways declared that no further financial support would be available, it could be concluded that there is no longer a positive forecast for Air Berlin, according to a statement by the airline.

It has submitted an application for insolvency proceedings to a local court against this background, Air Berlin stated.

Meanwhile, the German government has said to step in and plans to provide Air Berlin with a temporary credit of 150 million euros (177 million U.S. dollars), enabling the company to continue running.