US media have reported that a heat flash was picked up by an infrared satellite over the Sinai Peninsula at the time of the crash. The black box recorders taped unusual noises on the flight deck, say Russian sources.
The black box flight recorders on board the Metrojet Airbus A321 picked up an unusual noise on the flight deck as the plane flew over the Sinai Peninsula, Russia's Interfax agency reported on Tuesday.
"Before the moment of the disappearance of the aircraft from radar screens, sounds are recorded which are not characteristic of a normal flight," Interfax quoted an unnamed security source in Cairo as saying.
Shortly before Sunday's disaster, pilots and air traffic controllers held normal conversations, with no evidence of irregularities on board the flight from Sharm el-Sheikh to St Petersburg in Russia, the agency reported.
US satellites recorded a heat flash over Sinai at the time of the crash, several US television networks reported, but there was no evidence of a rocket launch.
One US official ruled out a missile strike on the plane because neither a launch nor an engine burn had been detected.
The infrared activity that was detected could mean many things, including a bomb or that an engine on the plane exploded because of a malfunction.
Aviation analyst Paul Beaver told The Associated Press that the heat picked up by the satellite "indicates that there was a catastrophic explosion or disintegration of the airplane," but it does not reveal what caused it. "It doesn't tell us if it was a bomb ... or if somebody had a fight in the airplane with a gun - there is a whole raft of things that could happen in this regard," he added.
Egypt's civil aviation ministry said there were no facts to substantiate assertions that the airliner had broken up in mid-air.
But spokesman Mohamed Rahmi confirmed that no distress call had been received before the crash.
Experts from Egypt, Russia and Ireland - where the plane was registered - were expected to conclude their last field inspection at the crash site on Tuesday.
Officials say it would take several months for the joint investigation team to produce the final report.
Meanwhile on Tuesday, Russia continued to bring bodies of the victims home.
mm/jm (AFP, AP, Reuters)