crashed

[Roger]

The math would be as follows: He decended from 1400msl to 600 msl in a left bank and accelerated 23 kts from the beginning top of his decending dive as noted on radar. It started at 148deg - at 156kts, and the next and last return was 62 deg at 171kts . If he maintained the same descent profile then it is: 23 x 450 / 800 = 13kts in additional airspeed at 150msl/ground = 184Kts +/-

My book says: Va 137KIAS at max gross: Do not make full or abrupt control movements above this speed. Further is says: Vno 168 KIAS : Do not exceed this speed except in smooth air, and then only with caution.

So unless this skymaster had an emergency chute that slowed it down in the last 450' of it's dive, than this was clearly a case of flying the aircraft way outside the parameters of Va, or even Vno

[Skymaster337B]

Even if the aircraft exceeded 171 knots, the normal engineering factor is 150% (also known as the "ultimate load limit"). So, the structure should have been able to hold together until at least Vne x 1.5 (for example 171knots x 1.5 = 256.5knots). If your aircraft tears apart right at Vne, then imagine how much damage you would be doing flying one knot below Vne. That's why there's normal an engineering factor of 150%.

However, if the structure was damaged it might not make it to 150% over, such as corrosion. I've found lots of corrosion in the wing tips before. It's possible. However, from my many accident investigations experience...it's usually a "change" that caused it. My Vegas odds are on improper wing tip modifications & or design. That's were I would start as an investigator.

Comments?

[edasmus]

Your comment sounds logical to me. I am certainly no engineer but it seems to me that flight control movement is very important as well. Meaning one could be operating at speeds well below Vne and even at Va and still damage the aircraft with abrupt control movements. My memory is a little fuzzy but I thought that the Airbus that shed it's vertical tail in New York shortly after 9/11 was at about 250KIAS when that occurred. I do not claim to know what the appropriate speeds are for passenger jet aircraft to maneuver around are but I believe by most standards 250 knots is relatively slow for that type.

I just want to add that though I think it is good to discuss this unfortunate accident we should all be patient and let the final report be published before rushing to any conclusions. I know we all want to believe our airplanes are safe and they most likely are but nonetheless a structural failure occurred and I certainly want to know why. It will take time to get these results.

Ed

[Skymaster337B]

I don't believe the "findings" of that Airbus accident....or TWA flight 800 either. But you are right, maneuvering can cause damage....especially at high speed. Assuming 137kts is the Va speed, then 137 x 1.5 = 205.5kts. That's faster than the 171 kts we're talking about, but with age/damage/corrosion, etc. the structure might not make it all the way to 150%. So, we'll see. But as an investigator I'd start with the wing mods.

[Roger]

A 4500lb car travelling at 180 mph experiences a 20G force if stopped in 50'. Now granted the accident aircraft did not "initially" stop in 50', but instead apparently changed his vetor angle at the bottom of the dive. An angled stop is less severe than a 90' stop as well. That being said if instead of "stopping" his dive he over pulled, then his vector angle change was more severe than a "stop", albeit beginning at an angle.

In the heat of fear, if he pulled this plane up at the last minute, especially given the large elevator on the 337 which will do a damn good job stopping or deflecting the descent, I can see the plane stopping it's descent in a distance that would cause some serious G's loading of the wings. Meanwhile if there were alterations to the tips and added weight of fuel in the tips, this is a no-brainer.

"Watch this"

[CO_Skymaster]

It is possible, in that last instant before wanting to hit the runway he could have pull back hard and created a peak load over the 150% structural limit on the wing. Extending the wing with the tip tanks could also increase the moment arm the load has to work on. It sounds like he was fully loaded with people and fuel and near max gross weight. There is also the possibility that he has done this maneuver many times before and over stressed the wing, creating fracture or deformation. This might have been the straw that broke the camel’s back.

[Kim Geyer]

I think at wing station 177 is where the autopilot bridle cables go through the wing spar