BERLIN/FRANKFURT (Reuters) – German airline Lufthansa (LHAG.DE) canceled hundreds of flights on Friday and warned of more disruption on Saturday after a cabin crew union started a series of walkouts that could become the longest ever strike at the carrier. On the first day of a planned week of protest over failed pension talks, flight attendants were instructed to strike at Frankfurt, Lufthansa’s biggest hub, and Duesseldorf between 1300 and 2200 GMT (0900 and 1800 EDT), affecting about 37,500 passengers.