The EgyptAir plane that plunged into the Mediterranean on Thursday had sent flight data through the Aircraft Communications Addressing and Reporting System (ACARS) from three different channels, indicating that there was smoke inside the cabin just before it crashed, France's air accident investigation agency said on Saturday.
According to flight data released by the Aviation Herald, which publishes information on the air industry, smoke was detected in the toilet and near the cockpit setting off smoke detectors minutes before it lost contact and crashed.
One aviation source said that a fire on board would likely have generated multiple warning signals, while a sudden explosion may not have generated any - though officials stress that no scenario, including explosion, is being ruled out.
The new information comes after the first piece of debris from EgyptAir MS804 was found in the Mediterranean Sea, along with human remains and personal belongings, the Egyptian military said on Friday.
The army published pictures on Saturday on its official Facebook page of the recovered items, which included blue debris with EgyptAir markings, seat fabric with designs in the airline's colours, and a yellow lifejacket.
Recovered debris of the EgyptAir jet that crashed in the Mediterranean Sea is seen with the Arabic caption "part of plane chair" in this still image taken from video on May 21, 2016. [Reuters]
Recovered debris of the EgyptAir jet that crashed in the Mediterranean Sea is seen with the Arabic caption "life jacket" in this still image taken from video on May 21, 2016. [Reuters]
Recovered debris of the EgyptAir jet that crashed in the Mediterranean Sea are seen in this still image taken from video on May 21, 2016. [Reuters]
Analysis of the debris and recovery of the black boxes are likely to be key to determining the cause of the crash.
The signals from the plane "do not allow in any way to say what may have caused smoke or fire on board the aircraft," said a spokesman for the French BEA agency, which is assisting an official Egyptian investigation.
He added that the priority now was to find the two flight recorders, known as black boxes, containing cockpit voice recordings and data readings, from the Airbus A320 which vanished from radar early on Thursday.
Aviation Herald published a burst of seven messages broadcast over the space of three minutes.
While suggesting a possible fire, the relatively short sequence of data gives no insight into pilot efforts to control the aircraft, nor does it show whether it fell in one piece or disintegrated in mid-air, two aviation safety experts said.
"The question now is whether the fire that caused the smoke was the result of an electrical fault - for example a short-circuit caused by damaged wiring - or whether some form of explosive or incendiary device was used - for example by a terrorist - to generate a fire or other damage," said aviation safety expert David Learmont.
The ACARS data suggested the fire had spread fast and "that might explain the fact that there was no distress call," Learmont wrote in a blog.
The aircraft was carrying 56 passengers, including a child and two infants, and 10 crew members, EgyptAirsaid on Thursday. They included 30 Egyptian and 15 French nationals, along with citizens of 10 other countries.