The Crash of Air Asia Flight QZ8501.

Last Sunday (28/12/14) an Airbus A320-216 call-sign QZ8501 disappeared from radar screens over the Java Sea on route from Surabaya, Indonesia to Singapore. Unlike Malaysia Airlines flight MH370 which disappeared in the same area in March 2013 I suspect that almost immediately the authorities had a good idea of the general area where QZ8501 had crashed into the sea.

Unfortunately though since then conditions in the Java Sea have been appalling making it very difficult to send out ships let alone send down divers to recover the wreckage. During this terrible waiting game I genuinely thought the most useful thing I could do was to change the subject to provide something else to talk about.

In the past couple of days though the weather has begun to improve slightly meaning that large sections of the wreckage have now been identified and up to 40 bodies have been recovered from the crash site. Therefore I think it is time for me to put forward my theory of what happened. However I should point out that the flight recorders have not yet been recovered so this is just a theory and could be subject to change as new information becomes available.

I should probably start with the basics. In fixed wing aircraft flight is achieved by forcing an angled wing through the air at speed. This creates an area of low density air above the wing and an area of high density air below the wing. When the force created by this high density air matches or exceeds the force of gravity then the wing lifts and flight is achieved. The problem is that air is not of uniform density so as you fly through it you sometimes hit pockets or air where even with the angled wing the density of the air doesn't produce enough upward force and gravity starts pulling the plane back to earth. If you fly a lot you are no doubt familiar with this pattern of a plane failing to fly for a moment and then recovering, failing and then recovering which is commonly known as turbulence.

The area that QZ8501 was flying through is known as the Intertropical Convergence Zone (ITCZ). In this area trade winds from the northern hemisphere meet trade winds from the southern hemisphere creating pockets of very dense air right next to pockets of much less dense air. When flying through these aircraft have to constantly adjust their speed to make sure they're producing enough lift. It can also produce very large pockets - tens of kilometres wide - in which the air lacks density to the extent that an aircraft of the A320's size cannot produce enough speed to generate the lift needed to maintain flight.

By the sounds of things QZ8501 encountered one of these large pockets - which can just suddenly appear - so requested permission to turn and climb to avoid it. Air Traffic Control (ATC) apparently gave permission for the turn but denied permission for the climb because there was another aircraft in the way. This seems to have prompted the pilot of QZ8501 to make the climb anyway but to do it slowly. This was a strange decision that creates two major problems. Always when a plane climbs it changes the angle that the wing is moving through the air (known as the angle of attack) reducing the density of the air beneath the wing and therefore the lift it creates. In order to compensate the aircraft needs to speed up to increase the flow and therefore density of the air beneath the wing.

So by deciding to climb slowly in an aircraft that was already having problems with lift it is likely that QZ8501's pilot has caused what is known as an aerodynamic stall where the wings don't produce enough lift causing the plane to simply fall from the sky under the power of gravity.

Obviously I don't want to lay all the blame on a pilot who is not able to defend themselves before I have all the information. For example if both of the aircraft's engines failed then that would also create an aerodynamic stall although that is a lot less likely. However I think that QZ8501 has crashed because of several elements beyond human control such as the weather combining to present the pilot with a series of challenges that he was not able to overcome. Therefore I think it was purely an accident rather then something more sinister or "just random, dumb luck" if you prefer.

Even if they have not been at fault in any way Air Asia are still obligated to compensate the relatives of the victims of the crash and that process has already begun. While I appreciate that this will be hugely expensive for Air Asia with it costing around USD90 million to replace the aircraft alone I think it would be a nice gesture if - on top of compensation - they were also prepared to meet the relatives out of pocket expenses such as hotel rooms and meals at least until the bodies have been recovered.

15:50 on 5/1/15 (UK date).