The Federal Aviation Administration also acknowledged publicly for the first time Friday that a United Parcel Service 747-400 plane that crashed in Dubai last month killing both pilots was carrying a large quantity of lithium batteries.
Since the early 1990s, there have been dozens of incidents of batteries igniting in flight. But it has not been known exactly what triggered many of the fires.
FAA now says recent research has identified heat as the trigger and is offering air carriers advice on how to reduce the risk of fire.
