Pilots at Lufthansa Group carrier Eurowings have been disrupting operations today with an eight-hour strike, in effect since 05:00.
The industrial action has affected services at Berlin Tegel, Dresden, Dusseldorf, Hamburg, Cologne and Nuremberg.
Pilots union Vereinigung Cockpit says the action follows discusions with Eurowings over job security, after Lufthansa opted to slash its fleet of 50-seat regional jets.
Crews are seeking an agreement to counter the effects of the decision. The union says the carrier could have a surplus of 180 pilots as a result, and that offers from the airline have been "inadequate".