The Metrojet Airbus A321-200 flight data recorder. (Russian Ministry of Defence)  Unusual sounds can reportedly be heard on the black box recorders of a Russian jet which crashed in Egypt, killing all 224 on board.  Flight 7K9268 plunged to the ground Saturday, 23 minutes after taking off from the Red Sea resort of Sharm-el-Sheikh on a flight to St Petersburg.  Investigators have begun examining the Airbus A321’s two black boxes, one of which recorded on-board conversations and the other flight data.  Russian news agency Interfax has quoted an Egyptian security official, who claimed the uncharacteristic sounds pointed to an on-board emergency before the crash.  "Judging by the recording, a situation on-board developed suddenly and unexpectedly for the crew, and as a result the pilots did not manage to send a distress signal," Interfax reported.  "Before the moment of the disappearance of the aircraft from radar screens, sounds are recorded which are not characteristic of a normal flight."  Russia has declared a day of mourning for the victims. (AAP)  Earlier, US media reported a American military satellite had detected a "heat flash" over Egypt's Sinai region at the time the airline plummeted to the ground.  Experts have said the fact that debris and bodies were strewn over a large area were signs the plane broke up in mid-air, a rare but not unprecedented event.  A militant group affiliated with Islamic State (ISIL) has claimed it brought down the plane.  Intelligence analysis has ruled out a missile strike, but US officials told CNN and other US television networks that a military satellite detected a heat flash at the time of the crash.  That could point to a catastrophic event during flight, possibly the result of a bomb explosion, although analysts were considering a range of possible causes, CNN said.  All 224 people aboard the flight died. (AAP)  Among other possibilities cited by the CNN report were the explosion of a malfunctioning engine, a fire caused by a structural problem on the plane or wreckage hitting the ground.  Egypt's President Abdel Fattah al-Sisi, who has dismissed the missile strike claim as ISIL "propaganda," said it would take time to establish the cause of the crash.  The probe could last several weeks or months if the recordings in the black boxes have been damaged, sources said. Russia's government commission overseeing the investigation was also due to meet overnight.  Airline Kogalymavia said the plane crashed due to "external action," and that there was no technical fault or human error. It insisted the aircraft was in an "excellent technical condition".  "When there is propaganda that it crashed because of [ISIL], this is one way to damage the stability and security of Egypt and the image of Egypt," Mr Sisi told the BBC.  "The plane was at 35,000 feet [10,668 metres] altitude. Believe me, the situation in Sinai - especially in this limited area - is under our full control."  The scene of the crash. (AAP)  Mr Sisi warned the probe could take years as in the case of Pan-Am flight 103 from London to New York that was brought down by a bomb and crashed into the Scottish town of Lockerbie in 1988.  "It takes time to clarify the incidents. You had the Pan-American that crashed over Europe. It took years before you reached the truth about the real reasons why it crashed," Mr Sisi said.  Search operations have been extended to a radius of 40km.
The Egyptian president has warned it could take years to establish what caused a Russian jet to crash in the Sinai Peninsula.