Update from a local news article:


The crew of the Cessna 208B had already done three days of test flights, but the day before the crash they ended early because one of the crew members felt ill. The crew went back up the following day and was testing the Cessna’s aft center-of-gravity stall characteristics when the plane crashed, the agency said.

Witnesses said the airplane broke up in flight and descended in a near-vertical corkscrew to the ground and several witnesses reported seeing a white plume of smoke as the airplane broke into pieces, the NTSB report said. The agency has previously said a wing broke away from the plane during the crash.

Two thoughts come to my mind with that information: If there had been a ballasting error, and the C of G was actually further aft than intended, recovery could have been an extra challenge. If the stall was allowed to develop into a spin (which may be inferred from the final very tight turn in the ADS-B trace), recovery would be demanding. If both factors were combined, it would be a great challenge for the pilots to recover.

I am responsible for not detecting a couple of ballasting errors during flight testing over the years, which has made me extra vigilant in that regard. I errantly accepted a "behind the aft limit" Cessna 185 for spin testing once, and it was immediately apparent that spin recovery was noticeably more difficult behind the aft C of G limit. Lesson learned!

Summary article in Flying Magazine here:

https://www.flyingmag.com/ntsb-relea...that-killed-4/

I’m sure, although possibly less so than one might imagine. I was involved in an airprox between two helicopters, whilst acting as an examiner/observer on an IF training session in one of them. I saw the other aircraft suddenly appear from behind the coaming in our 1 o’clock and slightly low. We were in his 7 o’clock, and converging, so totally out of view as he was single pilot. I started saying loudly “turn left, turn left” but there was no reaction. RHS pilot was fixed on his instruments and couldn’t understand why I was so upset about a 3 degree ADF divergence, LHS pilot I don’t know. In the space of about 5-6 seconds I went from calm, to surprise, to shock, to fear then to total relaxed acceptance of imminent death. Then the LHS pilot turned us left and we missed - my report said 20ft vertical and 50ft horizontal separation. The subsequent physiological reaction was intense! Point being, when you know you are actually about to die, it’s not as terrifying as you would expect!

In that dive the ADS-B GS reaches 197 kt in the dive. So the airspeed was probably faster and beyond Vne.

And this is the part of the equation which is alluding me a little... The airplane moved forward around 3000 feet while losing around 7000 feet of altitude, so more down than forward. If the "forward" is the base of the triangle, described as "groundspeed", and peaked at 197 kts, and the "down" is the altitude lost, the motion along the hypotenuse of the triangle would represent the actual airpseed?

Yes terrifying. Very sadly, there will be no memories of the crew. That said, having experienced my own terrifying experience when a training flight went wrong, I can say that I have very little recollection of it at all. Only enough, to know that yes, it did happen to us. That, and another extremely traumatic experience a couple of years back, which I know I witnessed in its full horrifying duration but do not recall at all, have me convinced that the mind simply turns off observation when things get really really bad. I hope this for the crew, as I would for any person experiencing sheer terror, with zero opportunity to mitigate it. The movies show us an increasingly terrified pilot hurtling toward earth and a certain death. That's the movies, I think (hope, anyways) that our actual life experience has some kind of built in protection for our emotions.

Take off from an oil rig, 125'ASL at rotation, massive explosion and glass screen of engine instrumentation turned seemingly all red, memory ceased at that point, memory regained on climb out when other chap asked "do you want me to cancel the audio tone", not aware of it until he asked, nor aware that he had put out a mayday during the dive for the water to gain airspeed.

Using two significant figures and 3,600 seconds per hour:

3000' ≈ .49 nm
7000' ≈ 1.2 nm
GS ≈ 200 kt

Time in seconds over horizontal 3000' ≈ 0.49 / 200 x 3600 ≈ 8.8

Speed over vertical 7000' ≈ 1.2 / 8.8 x 3600 ≈ 490

Speed down slope ≈ (200^2 + 490^2)^½ ≈ 530 kt

The structural failure may have happened before achieving this speed.
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Thanks RBF, I did my modest math, and got very similar results. I figured I must have made an error along the way, and set my results aside. Like a few other planes I've dived, the Caravan will build up speed very quickly when pointed down (as opposed to a few floatplanes I've dived, when once pointed down, I had to add power to achieve the required speed).

The two photos in the preliminary NTBS report do show the airplane descending vertically, probably already broken up, and they can probably validate the speed with those photos.

Not quite the same but in the Pacific GA forum TWT has posted this report which discusses what appears to be structural failure of a 210 wing in flight...