Official: Smoke Detected On Board EgyptAir 804, 'Priority Is to Locate Wreckage and Black Boxes'

— -- Smoke was detected from within the doomed EgyptAir plane shortly before it disappeared from radar over the Mediterranean Sea, ABC News has confirmed. Experts believe, that if accurate, this may point towards mechanical failure.

A spokesman for France's Le Bureau d'Enquêtes et d'Analyses (BEA) -- the agency responsible for investigating aviation accidents -- cited data from ACARS (Aircraft Communications Addressing and Reporting System) in confirming the detection of smoke in the aircraft. ACARS data is automatically relayed between the plane and the ground.

"We can confirm that we have seen ACARS messages from flight MS804 in which it is written that smoke was detected on board," said the spokesman. "At this stage we still do not know what happened on board. Our priority is to locate the wreckage and the black boxes.”

A U.S. A320 captain told ABC News that if ACARS (Aircraft Communications Addressing and Reporting System) data is accurate, it would indicate a fire in the plane -- specifically in the avionics bay underneath the cockpit.

Initially, when the ACARS data was published by aviation trade publication the Aviation Herald, Airbus said it would not "comment on any potentially leaked data" and would not "contribute to any kind of speculation in the frame of an ongoing investigation."

While it's too early to reach a conclusion, the ACARS data may be significant because it suggests other explanations for the crash beyond terrorism.

An A320 chief avionics mechanic for a major U.S. airline read the ACARS messages and told ABC News that if these messages are in fact accurate, they would suggest that the window heater computer in the avionics compartment went bad, initially sending faulty signals about the windows.

The computer may have short-circuited, overheated and started a fire, eventually leading to a total electrical failure on the plane, said the chief avionics mechanic, basing the assessment on the ACARS messages.

The missing EgyptAir plane was en route to Cairo from Paris when it disappeared early Thursday with 66 aboard. The plane lost contact with the radar tracking system at 2:45 a.m. at an altitude of 37,000 feet, according to EgyptAir. Search teams today scoured a wide area south of the Greek island of Crete for signs of the Airbus A320.

ABC News' Louise Dewast contributed to this report.