A sick-out by Air Berlin Plc pilots is threatening an immediate grounding of the insolvent airline.

“What happened today massively jeopardizes the entire insolvency proceedings,” Frank Kebekus, the airline’s general representative appointed by a court, said in a statement Tuesday. “Unless the situation changes in the short term, we will have to end operations and all efforts to reorganize.”

Air Berlin canceled some 100 flights after about 200 of its 1,500 pilots said they were unfit to fly, with many notifying their employer just before their scheduled departures. Air Berlin said that behavior resembled “playing with fire” and cost the airline several million euros.

With the deadline drawing close for investors to submit bids for Air Berlin, operations are facing increasing disruption. The carrier said Monday it will cancel numerous routes to the Caribbean and some U.S. flights from Sept. 25, and only customers who bought tickets after the company filed for insolvency on Aug. 15 will be reimbursed. The cancellations are a result of lessor AerCap Holdings NV repatriating 10 long-range aircraft leased to Air Berlin, Sueddeutsche Zeitung wrote, without saying where it got the information.

Air Berlin’s insolvency administrator will accept bids until Sept. 15, and the airline’s creditor committee will meet Sept. 21, possibly to decide how the company will be liquidated. Deutsche Lufthansa AG is so far the only carrier to say it handed in a bid.

Possible Bidders

Lufthansa Chief Executive Officer Carsten Spohr said last month the company may be interested in Air Berlin’s Austrian arm Niki, some but not all of Air Berlin’s long-haul aircraft, its cargo operations, and possibly even the company’s fleet of Bombardier turboprop aircraft. Hans Rudolf Woehrl, an aviation entrepreneur who sold various carriers to Air Berlin in the past, said Sept. 10 that he submitted an offer that may amount to 500 million euros ($597 million). Thomas Cook Group Plc’s Condor airline and EasyJet Plc are also said to be preparing bids.

Air Berlin has drawn interest from a crowd of less likely bidders with little industry expertise as well, including closely held logistics service provider Zeitfracht of Berlin. Utz Claassen, a former CEO of German utility EnBW, also indicated he might be interested in bidding, as did Niki Lauda, the founder of Air Berlin’s leisure arm and a former Formula One race-car driver.

Pilots union Vereinigung Cockpit in a statement said it was “surprised” by the events, and called on flight deck crews to go to work. AerCap spokeswoman Gillian Culhane said the company has no comment.

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Photo Credit: Air Berlin's pilots mounted a sick-out on Tuesday, crippling the airline's operations. Air Berlin, which has a large Airbus A320 fleet, is insolvent, and with pilots rebelling, it may stop flying sooner than expected. Jasper Juinen / Bloomberg