Cabin crew at German flag carrier Lufthansa walked off of their jobs on Friday, with a strike that began at midnight (2200 Thursday GMT) and that will affect hundreds of flights. Some 20,000 flight attendants have been called to strike until 10 p.m. on Friday. The UFO trade union called a one-day strike for its members both with Lufthansa and its Cityline regional subsidiary, as wage negotiations continue to stall. The walkout is Lufthansa's third major one this year. It follows two rounds of pilot strikes. How is the strike expected to affect travel? Lufthansa, Germany's largest airline, canceled hundreds of flights in advance of the strike, as it struggles to mitigate the impact of the walkout. Cancellations are expected to hit the hubs in Munich and Frankfurt, as well as other airports, including Leipzig/Halle, Berlin and Stuttgart.  At its largest hub in Frankfurt, nearly 75% of some 350 scheduled Lufthansa departures were canceled.…