Therefore, this seems to have been a misjudged intentional turn.
Could be anything. Stall/Spin? Structural failure? Pilot incapacitated?
One more thing. Why did he even turn? This was not an escape maneuver, the valley goes on in almost a straight line. Therefore, this seems to have been a misjudged intentional turn. Looking at the profile of his previous flight, that seems plausible. Doing this in mountain valleys at low altitude of course is risky business.
Actually the entry speed for a Chandelle isn’t excessive, eg 105 kts for a C172. The alternative is power and the guy was flying a 182RG which has plenty of power, so probably doable. That said, you need to be trained for it.
I did a huge number of those for the FAA CPL. It needs plenty of speed before you pull up. Yes, sure, if you have speed then you have even more options. There are all kinds of “aerobatic” turns, for those who know what they are doing. But all need speed. Abd most sensible people will slow down if there is terrain left and right – so they can do a tight turn.
You could also do a Chandelle.
It has to be more than just descending. You need to accelerate in the descent. It is quite doable if you have height, and if you unload the wings enough, you can do a really fast tight turn, safely.
A descending turn will reduce both radius and G force, if height is available. Start by climbing to reduce speed, which will build up in the descent. As you are turning down valley you can afford to go near to the ground. And use any extra width from side valleys if available.
There is the danger in any canyon turn that there is a downdraft on the side you are turning to.
It would be good if DMMS – defined minimum manoeuvring speed was better understood and practiced. Approximately 1.4 x Vs this equates to a level turn of around 45 degrees with some safety margin. Aircraft clean around 85KIAS, or 95 KTAS. Radius of turn formula is Velocity squared divided by 11.25 times tangent of angle of bank. This is a radius of around 250 metres, so not trivial in a narrow canyon. Carrying out the turn with flaps and 70 KIAS, would shrink the radius by around a half to 125 metres.
Very odd – why would he accelerate while trying to turn in a narrow valley? 100 knots is below Va so he would have stalled before he broke anything, and anyway you have a substantial margin beyond Va before anything breaks catastrophically (in theory).
If you slow down to just above the stall speed at your planned bank angle, you can make an amazingly tight turn. A long time ago I wanted to be sure of turning within the bay at St Jean de Luz, slowing down (in a DR400) to about 70 and pulling a 60 degree turn. I didn’t even enter the bay.
Seems like he lost 20kn while turning, probably hard. Plane was inside the valley and a turn at 100-120knot may be too large here. Either he pulled too hard and brake the plane, or not turn tight enough and break the plane with the help of the ground… Surroundings are 7200ft high.
