Several scenarios would explain the mysterious crash of the EgyptAir flight MS804 into the Mediterranean en route from Paris to Cairo early yesterday, but aviation experts say a terror attack is the most probable. Both France and Egypt have been leading targets for Islamist terrorists in recent months.In October, Islamic State claimed responsibility for bombing a Russian charter plane that crashed into the Sinai desert on its way from Sharm el-Sheikh to St Petersburg, killing 224 passengers and crew.MS804 is said to have plunged more than 6700m before spinning full circle and crashing into the Mediterranean off the Greek island of Karpathos. Two large floating objects in the Mediterranean were spotted by the crew of a Greek navy frigate yesterday afternoon. Pictures posted online purported to show debris from the airliner. But the head of the Greek air safety authority said last night that wreckage found ''does not come from a plane''.Greek defence officials earlier said pieces of white and red plastic, and two life jackets, were spotted close to an area from which a transponder signal had been heard.Sky News reported that the authorities were examining CCTV footage at Charles de Gaulle Airport. A ship's captainsaid he saw ''flame in the sky'' about 200km south of Karpathos.Egypt's aviation minister, Sherif Fathy, said the chances of an attack were "higher than the possibility of a technical [failure]" for the downing of the EgyptAir plane.Aviation experts agreed that there was little chance that a mechanical fault was responsible. The plane was put into service in 2003, making it relatively new for an aircraft that usually operates for 30 or 40 years."A major technical fault - the explosion of an engine, for instance - seems improbable," said aeronautics expert Gerard Feldzer.Jean-Paul Troadec, former director of France's Aviation Bureau of Investigation and Analysis, told Europe 1 radio: "It's a modern plane and the incident happened in mid-flight in extremely stable conditions. The quality of the maintenance and the quality of the plane are not in question in this incident."Experts also say it is unlikely the plane was shot down from the ground, as was the case with Malaysia Airlines Flight 17, which went down over Ukraine in 2014.The EgyptAir plane was flying at 11000m when it disappeared."We cannot exclude the possibility that it was shot down by another aircraft by mistake, but if it were it is likely we would already know," said Feldzer.The region around northern Egypt, including the coastlines of Israel and Gaza, is "one of the most monitored regions in the world, including by satellite. It would be very difficult to hide this kind of information," he added.That leaves a terrorist attack as the most likely possibility, the experts said, not least because it appears that no distress signal was sent from the aircraft."A technical problem, a fire or a malfunction doesn't cause an instantaneous accident and the crew has time to react," said Troadec."The crew didn't say anything."If a bombing is established, the question for investigators will be how a device was smuggled aboard a flight taking off from France's busiest airport, Paris Charles de Gaulle, which has been on high alert since last year's jihadist attacks in the French capital."A bomb placed on board in Paris or Cairo is possible because it is difficult to make an airport 100% watertight, even in an airport such as Charles de Gaulle," said Feldzer.FlightRadar24 indicates that the plane travelled to Egypt, Tunisia and Eritrea two days before the crash, raising the possibility that a bomb was put on board in Africa...