Flight KGL9268 crashed just 23 minutes after take-off. As investigators reach the wreckage Sky News looks at what we know and what may have caused the disaster.
:: What happened?
The A321 Airbus operated by a small Russian airline bound for St Petersburg took off from the holiday resort of Sharm el-Sheikh at 5.58am am (local time) carrying 224 people - mostly tourists.
At 6.20am flight KGL9268 vanished from radar screens while flying at an altitude of 31,000ft over the mountainous area of Arish and gone into a "rapid descent".
:: Who was on board?
Egyptian authorities say the plane was carrying 217 adults, 17 children and seven crew.
:: Is the A321 safe?
According to former head of flight operations at the Civil Aviation Authority Mike Vivian the aircraft has an "excellent safety record".
:: And the airline?
It's a small Russian airline, with only around six jets, that mainly operates internal flights and some holiday flights to Turkey and Egypt.
It is not on the EU blacklist of Russian airlines banned over European airspace and has had only one serious incident - in 2011 there was a problem with an aircraft on the ground which caused an accident killing three people.
:: Was it mechanical failure?
Unlikely, say experts. Mainly because of the the A321's good performance. Airsafe.com give it a mid-table ranking for with just 0.10 incidents per 1 million flights.
However, Egyptian authorities have suggested the pilot did contact air traffic controllers saying that there was a problem on board.
:: What else could have caused it?
Weather conditions could have been a factor, but there were no reports of poor weather in the area. In addition it could have been a pilot error. Again, experts say this is unlikely.
:: Terrorists?
Mr Vivian has said "hostile action" should not be ruled out but Egyptian authorities were quick to rule out suggestions the plane had been shot from the sky.
Russia last month launched military strikes in Syria against IS and other rebel groups fighting the Bashar al-Assad regime.
IS has control over some Sinai territory and other rebel groups in the region have sworn allegiance to the IS leader Abu Bakr al-Baghdadi.
:: What is key for investigators?
Rescue teams are now at the crash site and will be searching for the black boxes to help them gain greater insight into what happened in the short time before the plane began its rapid descent.
Experts say they will be looking for signs to tell them whether the plane broke up in the sky, which would suggest an explosion at altitude.
:: And survivors?
Rescue teams have said they can hear voices of people trapped in the plane wreckage.
Five children have been found dead, other bodies have been found still strapped in their seats.