Mexicana Airlines, the busiest foreign carrier at Los Angeles International Airport, announced Tuesday that it had filed for bankruptcy protection in the U.S. and Mexico, blaming much of its financial trouble on high labor costs. The debt-ridden airline made the announcement one day after suspending 31 flights at airports across the country, including in Los Angeles, New York, Chicago, San Jose, Sacramento, San Francisco and Oakland. At LAX, the airline put a hold on four of 15 daily flights to Puerto Vallarta, Guadalajara and Mexico City. The Mexico City-based airline promised to contact passengers with tickets on canceled flights for...