crashed

[WebMaster]

Originally Posted by jack374dn

According to the NTSB the wing seperated at Sta. 177 .. Out of interest, I am going to establish Sta. 177 on 74DN this morning ... I have install data on ?? tip tank installation unless it has been disgarded ... Will let all know my findings ...

74DN super skyrocket ... From first hand experience with the acceleration potential of my airplane @ less that 1000 fpm dive @ 2300 / 32" M.P... Roger's comment is my opinion is right on ... RED LINE + ...

I don't know if it is practical for you to do so, but could you place a marker of some sort on the wing, coinciding with Station 177, and then take a picture.
It would help all of us to visualize where that is, in relation to the strut and it's attach point.

Thanks,
Larry

See attached diagram for wing station's.

[edasmus]

"The last contact was at 15:47:00, the airplane was at 600 ft msl, on a heading of 062 degrees at a ground speed of 171 knots."

"The surface weather observation at BLM at 1535 was winds 250 degrees at 7 knots; visibility 10 statute miles; sky condition clear; temperature 03 degrees Celsius; altimeter 29.76 inches of mercury."

These statements are quoted from the preliminary report. This would support a conclusion of an indicated airspeed of less than 171 knots at this point. The aircraft most likely had a tail wind component at this point making the ground speed higher than the indicated airspeed. The winds, though light, appear to be from the WSW and the aircraft was heading ENE at last radar contact.

I, like the rest of you, had the same thought about a possible overspeed and abrupt pull up. Maybe that happened and maybe it did not. At the last radar data, he probably was not at an overspeed.

Does this make sense or do I have it backwards?

Ed

[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.