Originally Posted by
Pilot DAR
I'm not sure I accept that the fatal crash force was "between 3 g and 4.25 g." (page 27 of the AAIB report), I expect a much higher number for a .45 to .75 stop from 55 MIAS? My very modest search for a calculation result suggests as high as 65 G. A friend of mine similarly crashed his 150, similarly stopping in about 12 inches, near straight down. The coroner told me that his stop was in the range of 200 G.
In any case, a nose down vertical arrival will likely be fatal, regardless of seatbelt use.
55 KIAS was the proximated forward speed of the a/c, it was said to have "entered the dive at about 50 ft agl", there is no speed mentioned at impact.
While I agree with you that the deceleration seems to be a rather low number this is acknowledged in Footnote 7 of the report, also there's a reasonable amount of data that we're not privy to (for example the video frame rate/position of a/c on horizon at different frames) which could cast a different light on things.
That said, if we take the stated 'g' my (literally) back-of-the-envelope calcs suggest an approx speed at impact could be as low as 6-8kn... I've allowed a 'fudge factor' to take into account some other variables such as greater initial deformation of the ground (described as soft) and the a/c itself before they both returned to a static state. If this is the case, and given the injuries described, then it seems to me the occupant would have had a [greater] chance of survival had he been more fully restrained (as he likely could have been).
While the inner engineer is interested in the physics I need to say that I was horrified to read this report. I had my head in my hands thinking of all the things that went wrong here, the people affected, and the lives irreparably altered. So sad, so unnecessary, but is there anything more we can do to stop this sort of thing happening again? Is there anything new to learn from the tragedy?
FP.