his month, Dutch airline KLM began testing a program it calls Meet and Seat, allowing ticket-holders to upload details from their Facebook or LinkedIn profiles and use the data to choose seatmates. “For at least 10 years, there has been this question about serendipity and whether you could improve the chances of meeting someone interesting onboard,’’ said Erik Varwijk, a managing director in charge of passenger business at KLM. “But the technology just wasn’t available.’’ Relative latecomers to the social media party, airlines are quickly becoming sophisticated users of online networks, not only as marketing tools, but as a low-cost way to learn more about their customers and their preferences. With Facebook alone claiming nearly 500 million daily active users - more than 60 times the 8 million people who fly each day - KLM and others are betting that many of them would be willing to share their profiles in exchange, say, for a chance to meet someone with a common interest or who might be going to the same event.