The strike affects Germanwings flights departing on Thursday and Friday. However, Germanwings says it expects to operate more than 60 percent of its flights scheduled during the strike period.

It said 80 percent of passengers would reach their destination, but some could be booked onto another airline or the Deutsche Bahn rail network.

Current information on the strike can be found here. Germanwings has advised passengers to check online to see if their flights will go ahead.

The walkout mainly affects flights from Berlin, Cologne/Bonn, Düsseldorf, Hamburg and Stuttgart airports.

The Vereinigung Cockpit (VC) union announced the strike earlier this week, saying its recent attempts to mediate with Lufthansa had failed. The dispute concerns retirement benefits that Lufthansa wants to change for new pilots - while increasing the age at which pilots can take early retirement.

Currently, pilots can retire at age 55 and receive up to 60 percent of their pay until the normal pension kicks in at the age of 65. The union wants this to continue for all pilots. Lufthansa is in the process of expanding its budget operations as it undergoes restructuring in the face of heavy competition from low-budget rival airlines.

Lufthansa's main airline faced a string of similar strikes in 2014, peaking with two walkouts in the space of a week last December. The strikes wiped up to 200 million euros ($226 million) from the airline's operating profit for last year. A trade union for pilots and flight engineers, Cockpit has roughly 9,300 members.

jr/msh (Reuters, dpa)