Airline passengers learned an unsettling truth this month: Your property can be stolen, even at cruising altitude. In one incident, the son of actress Cybill Shepherd allegedly pilfered valuables from carry-on bags while flying cross-country from San Francisco; the 22-year-old was arrested at the Philadelphia airport. In another case, five travelers flying business class from Tokyo to Paris reported missing more than $5,700. The thefts occurred while they were sleeping.