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EgyptAir flight MS804 may have suffered an on-board fire just moments before the aircraft plunged off radar screens, according to an aviation industry publication.
Warning messages sent automatically by the Airbus A320's computer systems to ground stations show smoke was detected in a lavatory close to the cockpit shortly after entering Egyptian airspace on Thursday.
The Aircraft Communications Addressing and Reporting system messages also seem to indicate there may have been a problem with the controls and computers, critical to controlling the plane.
Sky News has obtained a screen grab of the data from EgyptAir Operations Centre's computer, which has time stamps that match the approximate time the aircraft disappeared.
Simon Hradecky of The Aviation Herald, a website that covers the civil aviation industry, explained to Sky News what the series of messages suggests.
He said: "The window sensors are all temperature sensors. Their activation suggests they went over-temperature - for whatever reason. So the right hand sliding window is at the start of the whole sequence indicating that the window became too hot - and this is why pilot discussions more and more focus on the right hand side of the cockpit as start of the fire.
"Then the lavatory smoke alert comes. The ATA Code is not completely known, it probably identifies which of the lavatories was affected. Everybody right now assumes it was the forward lavatory right behind the cockpit wall.
"Then the avionics smoke comes active, indicating the avionics bay, the room below the cockpit with all the aircraft electronics and all its computers, contained smoke. And now the right hand fixed window comes active (which is forward of the sliding window and better exposed to the oncoming air) two minutes after the start of the sequence.
"Then the systems start to crumble, all of which are in the avionics bay. So one can see how the heat/fire spread and affected the systems, and that pattern makes sense.
"Many pilots assume that there was a fire in the avionics bay just below the cockpit floor."
He added: "The smoke/fire was the first event in the crash sequence that started the crash sequence. What then happened is up to speculation until we know the contents of the cockpit voice recorder.
"However, the 90 degrees turn left is required procedure to get off the airway for an emergency descent (in order to not descend into another aircraft).
"The 360 degrees turn, as described by the Greek Defence Minister, is a good pilot manoeuvre to increase drag and thus accelerate the descent.
"In case of a catastrophic fire pilots will try to ditch the aircraft (if over water), and it would appear plausible that this is what happened."
Experts say answers will only come with an examination of the wreckage and the plane's cockpit voice and flight data recorders.
Search crews found floating human remains, luggage and seats from the jet on Friday, but ongoing efforts are being made to find large pieces of wreckage and the black boxes.
Egyptian authorities say they believe terrorism is a more likely explanation than equipment failure, and some aviation experts have said the erratic flight suggests a bomb blast or a struggle in the cockpit. But so far no hard evidence has emerged.
No militant group has claimed to have brought down the aircraft, in contrast to the downing of a Russian jet in October over Egypt's Sinai Peninsula that killed 224 people. In that case, the Islamic State group issued a claim of responsibility within hours.
Three European security officials have reportedly said the passenger manifest for the flight contained no names on terrorism watch lists. This has not been verified by EgyptAir.
French aviation investigators have begun to check and question all baggage handlers, maintenance workers, gate agents and other ground crew members at De Gaulle Airport who had a direct or indirect link to the plane before it took off, officials said.
Flight MS804 left Paris at 10.09pm BST on Wednesday but vanished at 1.30am on Thursday.
EgyptAir said on Twitter that radar contact with the plane was lost about 295km from the Egyptian coastline.
The European Space Agency said one of its satellites spotted a possible oil slick in the same area but there was no certainty it came from the plane.
An Egyptian paper has quoted the country's civil aviation minister Sherif Fathi as telling victims' relatives there are "no survivors".