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#16
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________ Ipad Cases Last edited by birddog : 04-09-11 at 06:03 PM. 
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#17
02-23-10, 06:41 PM
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NTSB Report Posted
__________________
Herb R Harney 1968 337C Flying the same Skymaster for 47 years
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#18
02-24-10, 06:27 AM
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Sad incident, but I find it interesting that even with the wing separating from the aircraft, the failure was out board of the strut, and the wing to fuselage integrity was not compromised.
It would seem to eliminate the need to remove the wings for Cessna's SIDs.
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#19
02-24-10, 07:22 AM
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Lets do a little Math
Reading the preliminary report, a couple of things struck me.
Radar showed it doing 171 KTS at 600 MSL, 188 degrees from the reported wind. KBLM is at 153 ft, MSL. So, he was 447 feet AGL. Presumably, he was descending, and building speed when radar track was lost, because reports are that he was about 50 AGL, or 203 MSL. At 171, with 7 kts of head wind, he was doing, and I know this is simplified, but he was doing 204 MPH IAS. I remember when Herb put his winglets on, that he had to remark the air speed indicator, because the winglets had a VNE of 201 MPH. So, before he got down on the deck and going really fast, he was already exceeding the VNE for the airframe.
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#20
02-24-10, 07:39 AM
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NY preliminary NTSB
So far this appears to be the classic example of why you never want to be in an airplane where the last thing heard by the pilot was "watch this".
He had apparently accelerated through 171 knots in his dive by the time he was down at 600' from his 1400' starting point going in the opposite direction. It would seem logical that if this dive run continued he would have been well over red line by the time he tried to pull up, and no one will ever know how quickly he (whoever was flying) tried to pull up. I could picture a 2000'+ fpm dive followed by an emergency yank back on the yoke once whoever was flying (or whoever took over) realized he may strike the runway. If that quick pull was done outside of the operating parameters of the aircraft "G" envelope, than this could be pure pilot error. And/or, does anybody know if the wing tip tank STC requires drilling through the internal wing structure, and if so, where does that drilling take place in relation to this break? http://www.337skymaster.com/messages...uote=1&p=15274
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#21
02-24-10, 08:43 AM
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Quote:
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 + ...
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#22
02-24-10, 03:14 PM
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Media Report On The Ntsb Release
__________________
Herb R Harney 1968 337C Flying the same Skymaster for 47 years
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#23
02-24-10, 06:26 PM
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It would help all of us to visualize where that is, in relation to the strut and it's attach point. Thanks, Larry
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#24
02-24-10, 11:23 PM
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See attached diagram for wing station's.
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#25
02-25-10, 12:34 AM
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"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
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#26
02-25-10, 01:29 AM
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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
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#27
02-25-10, 03:36 AM
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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?
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#28
02-25-10, 10:38 AM
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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
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#29
02-25-10, 10:57 AM
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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.
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#30
02-25-10, 12:05 PM
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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"
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