The U.S. assessment is not contained in a formal document, said a source, who emphasized the cause of the deadly crash remains under investigation.

A preliminary report released last week included detail about the fuel, saying that the fuel to the plane's engines appeared to have been shut off.

Captain RS Sandhu, a veteran pilot and former Air India director of operations, has been appointed as a domain expert in the ongoing investigation into the Ahmedabad plane crash by the AAIB