Germany's second-largest airline, Air Berlin, which declared bankruptcy last month after years of losses, was forced to cancel dozens of flights on Tuesday due to an unusually high number of pilots calling in sick. Air Berlin has been dogged by delays and cancellations, which have resulted in it paying millions of euros in compensation to passengers.
Lufthansa - which already leases 38 of Air Berlin's 140 planes - could buy up to 70 aircraft with as many as 3,000 crew for Eurowings, German media had reported.
Domestic and worldwide flights have been affected, stranding passengers.
The action comes ahead of a Friday deadline for interested bidders to submit offers to take over parts of the carrier.
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Air Berlin filed for insolvency in mid-August, after its main shareholder Gulf carrier Etihad pulled the plug on its cash lifeline.
Thomas Winkelmann claimed the move by almost 200 pilots to call in sick at short notice was "the equivalent to playing with fire" and would cost the troubled airline "several million euros". "A stable operation is mandatory for these negotiations to succeed".
They announced the cancellation of more than 100 flights on Tuesday.
"VC is convinced that talks about a social plan for an orderly staff transfer is the only way to safeguard as many jobs as possible", says the union, adding that it has urged its members at Air Berlin to honour obligations in their labour contracts unless there is an "acute reason" to call in sick. Germany's government has backed a €150 million ($179 million) bridging loan, and talks with potential investors are under way.