Air Berlin filed for bankruptcy protection last month after its biggest shareholder, Etihad Airways, withdrew funding following years of losses.
Parties interested in buying its assets have until Friday to submit binding offers.
On Tuesday, about 100 flights were cancelled after 200 pilots called in sick.
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Some short-haul flights at Lufthansa’s budget airline Eurowings were also hit because it leases 33 planes with crews from Air Berlin.
About 150 pilots called in sick on Wednesday, Air Berlin said.
The airline has said the...