The EgyptAir flight disappearance could be the result of a bomb, according to one of Australia's most prominent counter terrorism researchers.
Deakin University professor Greg Barton said while it is possible MS804 vanished on the way from Paris to Cairo because of a conventional systems failure, "if you have an aircraft experience an explosive decompression at cruise altitude, that points to it being a bomb".
He told news.com.au that other aircraft flying in bad weather have entered into a high-speed stall and a terminal spin due to human error (such as Air France 447 flying into bad weather from Rio de Janeiro to Paris in June 2009) but that does not appear to be the case here.
"If the radar image is suddenly not there and there's a sudden deceleration, as with the Sharm el-Sheik flight, it does strongly suggest a bomb."
The Sharm el-Sheik crash came in November, when Russian Metrojet Airbus A321 crashed in the Egyptian resort town just 23 minutes after departing for St Petersburg, killing all 224 passengers. Islamic State claimed responsibility for the attack.
Professor Barton said there would be "lots of capacity for exploiting the lax security" at Cairo airport and other North African airports where the aircraft had been earlier in the day.
While it would have been harder to plant a bomb at Paris Charles de Gaulle Airport, he said someone could have managed to conceal the device on a previous flight and set it to detonate 30 hours later.
He noted that France and Belgium also had a large IS element, with many individuals returned from the Middle East.
The Middle East expert said the current security situation in Egypt is "dire", with the authorities struggling to maintain control over its citizens.
"The government under Mubarak was repressive, under Sisi [president Abdel Fattah el-Sisi], it's worse. The regimen has totalitarian aspirations but not the capacity to achieve these aspirations.
"They'll pick someone off the street and beat the life out of them. It polarises society. IS has a strong presence.
"Even in Cairo and Alexandria there are elements more inclined than ever to fight back.
They're next to Libya, a failed state that's in chaos, and they don't have complete control over their borders."
The Federal Government's advice online is for Australians to "reconsider your need to travel to Egypt due to the threat of terrorist attack and kidnapping."
It says terror attacks could occur at any time, including in tourist areas.