The Russian Metrojet aircraft lost in north-central Sinai today was a leased Airbus A321 that entered service 18 years ago. Its reported passenger load was 224 people, which means its cabin was full or nearly full.

It had left the southern Sinai coastal resort town of Sharm el-Sheikh heading north for its destination, St Petersburg in Russia. Its route took it across Sinai – where the weather was good – and it would have continued northward over Cyprus and Turkey.

According to commercial flight tracking service Flightradar24 the aircraft was seen to suffer a disturbance which caused rapid variations in its speed and height, reducing the speed to 6okt at one point, which would put it into a deep stall condition unless the crew acted rapidly to recover speed again. Then the aircraft developed a high rate of descent – about 5,000ft per minute, and the position, height and speed information from the aircraft’s transponder was lost.

Flightradar24’s information about the Germanwings aircraft lost in the French Alps earlier this year proved to be highly accurate, and ahead of official information from the investigators it became evident that the A320 had  begun what looked like a deliberate descent to impact, and so it subsequently proved.

In this case the information is more complex because of the apparent speed and height variations that preceded the fatal descent.

The Egyptian authorities have been quick to rule out terrorist action in the form of sabotage or a missile strike, but it is too soon to rule anything out. Sharm el-Sheikh is an important Egyptian tourist resort, and any suggestion of security breaches affecting travellers there would be harmful to trade.

The aircraft was cruising at 31,000ft, at which it would be safe from the kind of man-portable missiles that terrorists in the area could obtain fairly easily, but the aircraft was 2,000ft lower than the Malaysia Airlines Boeing 777 that was shot down over eastern Ukraine last year by a more powerful ground-launched missile.

Early information suggests the aircraft came down in one piece and broke up on impact, making the missile strike theory less likely. On-board sabotage, however, does not have to break an aircraft up in order to damage its controllability.

So at this point it is certain that the aircraft suffered a serious upset during the cruise, but there is no indication why that occurred.