Air Algerie flight with 116 people on board has dropped off radar, prompting a search for the missing plane, the airline's operator said Thursday.The plane, an MD-83, was carrying 110 passengers, two pilots and four crew members. The MD-83 is part of the McDonnell Douglas MD-80 family of twin-engine, single-aisle jets. The plane belongs to a private Spanish company, Swiftair, but it appears to have been operated by Air Algerie. Flight 5017 lost radar contact 50 minutes after takeoff from Ouagadougou, Burkina Faso, early Thursday. It was supposed to arrive at Algiers' Houari Boumediene Airport about four hours later.