According to the airline, an "indication of a mechanical issue in an engine" prompted the flight crew to divert the Airbus A330 to an Air Force base in the Azores. It is a remote chain of islands off the coast of Portugal. "Seeing all the emergency vehicles lining the runway, it reminded us it was a potentially dangerous situation," Elder said.

Airlines stocks took off on Thursday, boosted by Delta reporting better-than-expected earnings and reinstating its full-year guidance. Here are the key chart levels to monitor for shares of three major U.