Final communications with AirAsia’s QZ8501 show that at 0612 local, the captain asks to divert around heavy weather by turning left from a heading of 313 degrees to 264 degrees, which is a 50 degree left turn. If we gauge that the plane eventually slows down to 353 kts as indicated by ATC, we’ll average 420 kts over the duration.

At an average of 420 kts (slowing down from cruise), QZ8501 cover roughly 7 nautical miles per minute, or 14 miles over 2 minutes. 1 minute after requesting the left turn, QZ8501 is roughly 7 miles off course to the left when the Captain also requests to climb. This indicates that the change in direction did not seem to reduce the bad weather. In this direction, QZ8501 would have had a tailwind of about 40km/hr, meaning if it was encountering any hail, this direction would have had the plane encountering less force going with the wind direction of the hail. The disadvantage would have been increased stall risk.

The captain is asked for his desired altitude, to which he requests FL380. By this point, the turn is already completed. So there is no issue with having both climbed & turned at the same time. Yet, as QZ8501 is now headed west on a heading of roughly 264 degrees, this means that it will intersect the course of the nearby AWQ502 which is already at FL380.

Another minute passes by and by 0614 local ATC responds that they’re authorized to climb no higher than FL350. There is no response to ATC’s directive. Yet by ATC’s last contact, we can clearly see that QZ8501 is at 36,500 feet & climbing beyond the authorized 35,000 foot level.

Is the lack response due to the fact that the pilot has already climbed beyond the authorized level? Or because an emergency has already begun?

Was the reduced airspeed an indication of intentional speed reduction due to hail? Or was it due to fast vertical climb to get out of the storm? And/or due to engine problems during the climb?

In my opinion, what we’re looking is one or a combination of the following:

Stall

Dual engine flameout due to hail/icing + auxiliary power failure (has occurred in the past w/these engines)

Decompression & mid-air break up

The problem with the stall scenario is that we would have at least expected there to have been a mayday call. Of the three bodies found so far, none had life-jackets on and at least one had no clothes, which is common during free fall.

My current best guess is that we’re looking at a decompression event related to the heavy high altitude thunderstorm (hail), and a change in altitude from FL320 to FL380. This may have also been complicated by a dual engine flameout which could have been worsened by an auxiliary failure. If this occurred while in a climb, then you’d also run into a stall. The temperature at the time in 36,000 foot air was -39C (250 hPa). So the chances for any hail/icing seem extremely high.

The general idea is that storms are less intense the higher you go, or that you can fly over them. Also, hail tends to get bigger as it falls, meaning it’s more dangerous at lower altitudes. The worst possible position to be in would be to be climbing into the wind. Climbing while flying with the wind would be a less forceful ascent in hail conditions than flying into the wind. However, the vertical component of the falling hail would produce more force when converting horizontal vecolity to vertical velocity. The difference in +/- 40km/hr wind direction is only a small component of the mostly downward velocity of mostly downward falling hail. And the original heading of 313 degrees was more of a tailwind (120+180=300 degrees) than the new 264 degree heading. Converting QZ8501's horizontal velocity of 450–350 kts into a vertical velocity in a 2000ft/min climb in affect gives any downward falling hail far more force than a change in wind direction relative to the heading of the aircraft.