This picture of an engine of the Avro RJ85 may provide a vital clue to investigators. Photo credit - AVHerald / CCAA
Update - this article was written before investigators confirmed that the aircraft appeared to have run-out of fuel. There are also reports of electrical failure - however this is quite misleading. The most likely scenario would be that the aircraft running out of fuel would cause a loss of power to the electrical systems.
On Monday, an aircraft carrying the Brazilian soccer team Chapecoense crashed whilst towards the end of its flight to Medellin.
We asked an experienced commercial pilot, who asked to remain anonymous, for his opinion on what might have happened.
''It's always a risky business to speculate on what might have happened to an aircraft involved in a crash so soon after the event took place.
Official investigations normally take several years to publish final reports, partly because it really can take that long for all of the evidence to come to light and for the circumstances to become clear.
However, even at this stage, there are several clues that the investigation teams will be considering.
Firstly, the aircraft in question is a very safe and reliable model, the Avro RJ85. The specific plane had a history of being operated by reputable carriers (Mesaba on behalf of Northwest in the USA, Cityjet on behalf of Air France in Europe). This aircraft did not simply 'fall out of the sky' as some media outlets would have you believe.
Indeed, there are some unusual aspects of its wreckage that provide the clues that I mentioned a moment ago. There are three that are of particular interest.
In an impact which results in such devastation of the airframe, we would expect there to be an explosion. Yet, on this occasion, none happened.
Bearing in mind that a jet engine blade would normally spin thousands of times a minute, we would expect this component to be particularly badly damaged on major impact with terrain. One of the engines of this aircraft is pictured above - you can see that it is actually remarkably intact.
Finally, the aircraft was flying a route of some 1,600 nautical miles, which is exactly the same as the maximum range of the Avro RJ85. Bearing in mind that we always carry a lot of extra fuel (for diversions, bad weather and so on, and then emergency reserve) it is extremely unusual that this flight was attempted without refueling.
We know that it was put into a hold whilst another aircraft carried out a priority landing. This accounts for the 'circling' that you can see on a map of the route that was taken. Do the lack of a fire, the relative lack of engine damage, and the extraordinary route length relative to the capabilities of the aircraft, suggest that it simply ran out of fuel?
Potentially, there are strong similarities in this scenario to Avianca flight 52, which crashed on approach to New York's JFK airport in 1990 (having taken-off from Medellin, coincidentally) due to simply running out of fuel. As I say, we take great precautions when it comes to fuel load so this situation should simply never happen - and to the best of my knowledge has not been the cause of such a serious incident since Avianca flight 52.
This is a question that the investigators will consider for many months and even years, and I can't pretend that I can answer it now. However, it is certainly an interesting thing to consider.''
Update - Audio of the air traffic control conversation between the flight and airport is now available with English subtitles. This makes clear that the flight crew declared an emergency just a few minutes before they confirm that they ran out of fuel. This would seem to be at odds with rules that state you should declare a fuel emergency as soon as you are using your last 30 minutes of fuel. Warning - some viewers may find this video distressing.