Scammers are posting messages on Facebook falsely claiming to be giving away free flight tickets, last week at KLM, this week at Brussels Airlines. Brett M. Christensen from website hoax-slayer has written a detailed report on this plague.
The posts have no association with the airlines they name and those who participate have absolute no chance to receive the free tickets. If one of these fake airline ticket giveaway posts appears on your Facebook feed, do not click on it. And tell the person who posted it that the giveaway is a scam.