FRANKFURT (Reuters) - A Berlin court on Thursday asked a higher court to rule on a legal challenge to the insolvency filing of airline Niki, which could derail the sale of the Air Berlin (>> Air Berlin Plc) unit to Britain's IAG (>> International Consolidated Airlines Group).

According to a statement by Berlin's civil courts, the Charlottenburg court still believes that Niki is in its jurisdiction, after Fairplane, a group representing airline passengers, sought to have the carrier's insolvency proceedings shifted to Austria from Germany.

(Reporting by Maria Sheahan; Editing by Christoph Steitz)