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Help researching 1961 Electra crash

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Help researching 1961 Electra crash

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Old 31st Jan 2018, 01:30
  #381 (permalink)  
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Originally Posted by Concours77 View Post
An intact tail will be feathers to the arrow, always.
I understand your point, but you can throw an arrow backward like a dart and it will take eight or ten feet to turn around.
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Old 31st Jan 2018, 17:49
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I've uploaded a video showing how the sim behaves if the CG is moved five feet forward. It makes a drastic change, and the plane behaves much more as Concours77 was expecting. It is not how N137US behaved, of course.

The precise numbers are probably not important, since there's so much uncertainty in the sim in the first place. It's an approximation of the plane behavior, and I've drastically altered the plane to simulate the damage. So the sim's value is in showing broad trends and ideas.

As I say in the video, if this behavior is the explanation behind how N137US got to the final wreckage site, then N137US behaved more like a sim with the 20 foot CG displacement than 15, regardless that the real life displacement was some different value.

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Old 5th Feb 2018, 18:57
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I'm working on illustrations for my next published version, and just finished a couple examining the CG for the whole plane and for the plane after losing the engines and forward fuselage.

The whole plane graphic will be part of the knife edge flying discussion. I wanted to get a feel for the forces involved. It's at https://ibb.co/cZNvWH

The damaged plane graphic is to help understand the dynamics after the first impact as discussed above. I guesstimated that the CG would move aft about 20 feet. I guesstimated the center of pressure using a simple cross section area calc, which doesn't take into account things like drag around sharp edges. So I wouldn't trust those values within less than a few feet. But it shows that the new CG and CP are pretty much lined up, which is why the sim would be highly sensitive to moving the CG a small amount. It's at https://ibb.co/iWvSdx

The second one has a couple things I'll fix before putting it in the report.
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Old 6th Feb 2018, 01:44
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Craig

I fear you may be heading up a blind alley with these weight and balance figures. They are immensely important with regards to straight and level flight, but I have to question their relevance during the break up sequence.

Contact with the embankment removed several outboard feet of the starboard wing. Initial contact with level ground appears to have removed the nose and in all likelyhood most of the remainder of the starboard wing if the bank angle was actually around 90°, which of course you dispute.

This means that the remains of the aircraft would be very asymmetric, making a nonsense of any calculations based on all or part of an intact airframe.

It is necessary to start somewhere with the calculations, but I think this will be a much more complex matter than just considering a change in the centre of gravity caused by the loss of parts of the aircraft. I do not consider this can be a valid aproach to modelling the final disposition of the rear fuselage and wing box section unless it can be worked out for varying degrees of bank from level flight to at least 90° of bank. 10° increments would suffice to show the broad distribution of wreckage resulting and may contribute towards establishing exactly at what angle of bank the aircraft struck the ground. That is to say, whatever angle of bank calculation best fits the distribution of wreckage actually found at the scene will go some way to providing a definitive answer to whether the aircraft was levelling out or the bank remained completely uncontrollable.
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Old 6th Feb 2018, 17:56
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As to..

Agreed as to parameters of controlled flight. Motion of any body that has no aerodynamic stability, or stable CG cannot be predicted without a great deal of data. In the sixties, the supercomputer was an infant, and chaos was also in infancy.

The CAB had a purpose outlined in its remit. After the third impact, nothing was quantifiable such that a reward of any kind could be had relative to “preventing” such an accident in the future.

The single cable system was the underlying culprit, and nothing could be done to make it redundant, certainly not at reasonable cost. The “fix”, one assumes, is more frequent inspections (not terribly difficult) involving pulling up some carpet and removing an Inpanel. More stringent repair procedures were no doubt applied, etc.

No mention of the two terrible accidents that were seemingly cured by LEAP, and I find that strange. The experiment involving flap/aileron, done by Lockheed, in my opinion, was done to eliminate the possibility that the wing had been partially destroyed, either prior to, or as a result of, the last take off.

Howl as much as you like, Whirl Mode was on everyone’s mind, and purposely not bringing it up was a political move.

IMO
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Old 6th Feb 2018, 20:01
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The graphic labeled "Knife edge flying" was intended to show the forces involved. It's interesting that it would take about 24,000 lbs of force on the rudder to do this, and I don't seriously contemplate that it happened or that the structure could stand it if it were attempted.

The balance issues for the broken plane are totally relevant. I agree that in a 90 degree bank more of the right wing would have been lost, but the CAB said it survived to WS 293, which is nearly to the number four nacelle. In the final wreckage the number three nacelle is clearly intact on its underside. The remains under where the rest of that wing burned confirms that there was wing past nacelle three. That's one of the best arguments that it wasn't in a vertical bank.

I have found varied evidence that the plane was in a shallow bank. If anyone wants to do the modelling to show what an Electra in a vertical bank would do, they're free to do so. The Argentine crash gives a good example of an Electra crashing in a vertical bank. My goal is to adduce evidence for what I think actually happened. I've run through many possibilities, now I'm working on presenting my case.

The purpose in running a sim on the broken plane was to find out what it would do in its damaged state. The result was so striking that I animated it that way, and it's very much like seeing a hydrofoil blow over. It's not a matter of treating the CG as the only important aspect, but of seeing what the CG change would do. It's certainly a valid question.

The difference between that and my animation of the CAB scenario is obvious, and I think anyone viewing the CAB animation would dismiss it. The sim is evidence (though thin) and the animation is illustration.

As for whirl mode, it was never a possibility. My mom got regular updates from people involved and she kept us informed. Whirl mode was not on the table in any way.

The sound of an engine in heavy whirl mode vibration is distinctive, the prop tips can go supersonic, and it was never reported. Everyone was aware that the Electra had a troubled history, and they wanted this solved fast so the public could be reassured. But whirl mode was not in the scope.
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Old 6th Feb 2018, 23:10
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More...

Hello,

From the (sim) angles alone, my guess of angle of Bank at RR embankment impact is no more than forty degrees, likely less.

The angle of crossing included with angle of descent, plus dihedral makes sense only if the scar is in the vertical. A ninety degree bank is impossible, with the reported orientation of the airframe, as it involves flight characteristics that involve nonsense. If head on, the aircraft would have been ninety degrees PLUS dihedral.

That there was wing left out to the fourth nacelle shows the engine parted with the wing? The engine is not part of the wing structure, it rests atop the upper wing surface.

Had Whirl Mode been “on everybody’s mind”, CAB made a decision not to address it. You have evidence Whirl was actively eliminated, or just dismissed? “Well, we can eliminate Whirl Mode.....” Erm, exactly why?

I have proof via my own eyeballs that Whirl Mode continued through 1969. LEAP did not eliminate the phenomenon; it added structure that was supposed to prevent it from damaging the aircraft.

The gearbox/torque shaft/engine was a pile driver, capable of tearing the three connected structures free of the original mounts.

“We’ll add an additional torque strut, and embellish the mounts...” Lockheed

“The battery catches fire, ok. We’ll enclose it in a steel box....” Boeing
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Old 7th Feb 2018, 00:29
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Thanks megan, for the links. I am trying to suss my misunderstanding of Whirl Mode. I think I stated the phenomenon is common, and not unique to the Electra.

The concentration of power/mass locally (well forward of the wing) cannot be dismissed. The propellors are heavy, and have an unusually long moment arm related to the forward wing spar. It provides an extreme and asymmetric increase in power translated during whirl, relative to other installations. My experience with Whirl Mode occurred on short Final, as pilot selected full power to make up for an undershoot. The articulation of the nacelle was extreme, I promise you it was profoundly distressing to this passenger.
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Old 7th Feb 2018, 12:13
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Originally Posted by Concours77 View Post
That there was wing left out to the fourth nacelle shows the engine parted with the wing? The engine is not part of the wing structure, it rests atop the upper wing surface.
We don't know what happened to the engines. The ALPA report said engine four separated from the wing at the tracks. It doesn't say where it ended up. The Chicago Tribune said three engines were found close together and one was in deep mud. The reporter clearly got it wrong, since he identified the left inboard and the number two engine as two different engines.

You have evidence Whirl was actively eliminated, or just dismissed? “Well, we can eliminate Whirl Mode.....” Erm, exactly why?
No evidence, just recollection. Everyone knew about whirl mode, and it was never discussed as being considered in this crash.
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Old 7th Feb 2018, 14:13
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The two previous whirl mode crashes involved structural failure of the wing at the wing root and subsequent loss of a complete wing while the aircraft were still in the air. That was clearly not what happened here as both wings remained attached even after striking the railroad embankment. Whirl mode can therefore be dismissed as a factor in this accident.
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Old 7th Feb 2018, 14:49
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Electra LEAP

The first thought on someone’s (objective) mind would be Whirl Mode.

Absent the main spar couple at low Hertz, the power line (especially outboard) can inflict serious damage to the wing, especially the more sensitive, less reinforced structures, specifically the piano hinges at the ailerons. This type of hinge is light, easy to service (exposed), and relatively inexpensive. It is efficient in the distribution of stress, but falls short of a design consideration that might include profound asymmetric vibration.

As I stated before, Lockheed’s “experimental” test of Flap/Aileron fouling was not to do with aerodynamic loads. That ship sailed in 1957, and no unknown “spill” or vortex generated stresses were unknown.

It was specifically designed to “exonerate” engine/propellor induced damage to the aileron. That is why the jack was removed from the experimental system.

Any success with FOIA?

Of importance would be the eyewitness accounts of the “engine noise” alteration(s). Again, most of the noise produced by a heavy turbo prop is propellor related, and any changes in tone would suggest pitch change (isolated to one system?). Something to look for would be oscillations in tone and volume, (surge) which would suggest problems related to thrust, and especially (if found) a system which has lost its steady state.

The rolling release, the turn onto the center line, the known Slop in the primary cabling, and the damage signature on the aileron suggest an early failure, at full power. An early and uncommanded roll would have had everything to do with lack of climb angle (who has time to increase pitch with such a serious problem showing up, and especially if one is considering an abort of the takeoff?) and also the very early “turn”.

edit. As a student pilot when I encountered the Whirl Mode on the Electra (as a passenger), I was thinking about p-factor as a source of vibration, since it would have been changing rapidly with each rotation of each blade. The propellors angle of attack would have been chaotic, to say the least. The noise we heard in the cabin was from Hell....

Last edited by Concours77; 7th Feb 2018 at 15:00.
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Old 7th Feb 2018, 21:12
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Originally Posted by G0ULI View Post
The two previous whirl mode crashes involved structural failure of the wing at the wing root and subsequent loss of a complete wing while the aircraft were still in the air. That was clearly not what happened here as both wings remained attached even after striking the railroad embankment. Whirl mode can therefore be dismissed as a factor in this accident.
Hi Gouli,

Whirl mode is what leads to wing loss, but only if there is a wing flutter component attached. There needs to be a (wing) sympathetic flutter concurrent and matching at low Hertz. These “partners” exacerbate the stress beyond just mount Slop, and beyond structural limits.

What I saw in 1969, (post LEAP), was a widening divergence from center thrustline, which got to what I estimated was a fifteen degree deflection, each way, for a total of thirty degrees “back and forth”. We were landing and in still air; I still noticed the wing twisting in three separate directions about its spar. As soon as the thrust went to idle, the show stopped.

I am trying to point out that not losing a wing does not eliminate Whirl Mode as a possibility as cause of aileron damage.

Would you care to comment? On the flap/aileron experiment?
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Old 8th Feb 2018, 00:33
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Concours77

I can envisage a situation where a developing whirl mode might cause an incorrectly assembled aileron cable to break. The vibration and flex of the wing adding just enough stress to part a misassembled joint.

Since all aircraft wings are designed to flex, often by several feet at the wingtips, the designers would have taken this into consideration when planning the control cable run for the ailerons. They would assume in their calculations that everything was assembled correctly and in good condition.

You propose a plausible mechanism as to how the aileron cable broke when it did, but the root cause was still incorrect assembly and ajustment by the ground engineers.

As far as the flap and aileron experiment is concerned, I believe that it was conducted to ensure that neither part could significantly interfere with the other. I don't think it was conducted to see if whirl mode was more likely at certain power settings as a series of experiments had already been carried out to determine the cause of the two previous whirl mode accidents where aircraft lost their wings. Then there is the question of whether flap would reduce the ability of a disconnected aileron to return to a neutral position in the slipstream. Clearly in this case, the ailerons remained displaced, so it was important to determine why this happened. I believe that it was determined that the ailerons were held in place by residual hydraulic pressure from the boost system. Once the control cable separated, the valves would have remained at their last commanded position.
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Old 8th Feb 2018, 15:02
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Originally Posted by G0ULI View Post
Since all aircraft wings are designed to flex, often by several feet at the wingtips, the designers would have taken this into consideration when planning the control cable run for the ailerons.
Bear in mind that other than the aileron trim tabs there was no cabling in the wing. The cables ended at the boost unit.
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Old 8th Feb 2018, 23:42
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Originally Posted by G0ULI View Post
Concours77

I can envisage a situation where a developing whirl mode might cause an incorrectly assembled aileron cable to break. The vibration and flex of the wing adding just enough stress to part a misassembled joint.

My experience involved other than standard “flex”. The wing was “twisting”, in spiral fashion.

Since all aircraft wings are designed to flex, often by several feet at the wingtips, the designers would have taken this into consideration when planning the control cable run for the ailerons. They would assume in their calculations that everything was assembled correctly and in good condition.

Yes, but there are no cables in the wing. Rods, running in sleeved ball bearings. Aileron Trim is by cables, I believe.

You propose a plausible mechanism as to how the aileron cable broke when it did, but the root cause was still incorrect assembly and ajustment by the ground engineers.

Well, the cable did not break, it separated at swage/connector/turnbuckle. CAB claim the cable parted at the forward junction block, between the turnbuckle and the pulley carriage.

As far as the flap and aileron experiment is concerned, I believe that it was conducted to ensure that neither part could significantly interfere with the other. I don't think it was conducted to see if whirl mode was more likely at certain power settings as a series of experiments had already been carried out to determine the cause of the two previous whirl mode accidents where aircraft lost their wings. Then there is the question of whether flap would reduce the ability of a disconnected aileron to return to a neutral position in the slipstream. Clearly in this case, the ailerons remained displaced, so it was important to determine why this happened. I believe that it was determined that the ailerons were held in place by residual hydraulic pressure from the boost system. Once the control cable separated, the valves would have remained at their last commanded position.
By “significantly interfere” is your meaning aerodynamic interference (Which would have been known, via wind tunnel testing in design) or mechanically, flap fowling aileron at inboard pocket rib? The scar found on the aileron would represent evidence of my theory, that the aileron flap “joint” was closed, due fouling of flap in its track, or aileron due to separated hinge?

With boost active, the Ailerons, Rudder, and Elevators return to neutral without stick deflection, by design. It’s in the manual. This is how we know the cable did not separate; had it separated, the aileron would have returned to neutral (without damage present). Boost ON or OFF. Ailerons do not need a reversal command to return to neutral.

Last edited by Concours77; 8th Feb 2018 at 23:48. Reason: Sorry, I should read up to current before I post.
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Old 9th Feb 2018, 14:46
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Originally Posted by megan View Post
I'm afraid you don't understand the system. A control surface always requires a reverse command to return the surface to its neutral point, matters not if its boost on or off. Thats presuming you keep your hands on the controls. Removing your hands the controls will return to their trimmed position. The boost pilot valve is the one that returns to its neutral point after the control movement has taken place.The aileron deflected because of the fact the cable separated and the remaining attached cable imparted a right wing down command.
I’m afraid you don’t understand my comments. Hands removed from controls return the control surfaces to neutral, unless trim is supplied through the (unboosted) Trim cables.

With “no authority” due to “separated” control cables, the ailerons should have returned to neutral. Reversal of control to roll left had no effect because the co-pilots cable had separated and de-tensioned the system, and foreclosed a roll left, OR right.

Neither (remaining) control cable had any effect, the system was without continuity, there was no ability to roll either direction, to increase, or release right roll.

That is based on the CAB finding, which I disagree with. The roll remained constant, and irreversible, due to a damaged aileron locked at three degrees up.

Boost had nothing to do with it, neither did a remaining and fully untensioned primary control cable.

Without any effect in aileron, Electra pilot’s release the wheel, to allow the control surfaces to regain a nested and neutral position; I find it unlikely there was aileron trim in play, either aileron up, or down.

Which is interesting, because in fifty years of hindsight, aileron Trim May have saved the day, since it was the only remaining authority in Roll, as demonstrated both by the report, and by me. In the CAB’s case, it is suggested only by its omission from the report?

Oops. I reread my comments. Left out is the part about hands off. It was my intent to say the ailerons return to neutral hands off, it is in the manual. Read the manual?

Last edited by Concours77; 9th Feb 2018 at 14:51. Reason: Blunder, and correction
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Old 10th Feb 2018, 03:08
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Standard aviation design notes suggest that the rudder be capable of resisting full aileron deflection on single engine aircraft or an outboard engine failure with other engines developing full takeoff power on multiengine aircraft at speeds 1.2 times the stall speed.

Either the Electra design was flawed in that respect, or the ailerons were or became deflected and held at considerably more than three degrees.
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Old 10th Feb 2018, 15:14
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Originally Posted by G0ULI View Post
Standard aviation design notes suggest that the rudder be capable of resisting full aileron deflection on single engine aircraft or an outboard engine failure with other engines developing full takeoff power on multiengine aircraft at speeds 1.2 times the stall speed.

There is so much to discuss in this comment. First, I agree. Second, the Electra we discuss had ample airspeed to invest the Rudder with sufficient authority to overwhelm the ailerons. Add asymmetric thrust (reduce portside) and the initial recognition of a problem, and we have nothing to push around here.

Either the Electra design was flawed in that respect, or the ailerons were or became deflected and held at considerably more than three degrees.
I think there was something gone wrong that made recovery unsussable, if at all possible. The three degree scar/artifact in the inboard closing rib means only that was deflection as the wing tip folded back around the trailing edge, forcing the take off set flaps to crush the pocket together. There is a caveat, depending on any angle we must add to include the flap angle to chord that may have been zero degrees, in actuality. Flaps set to takeoff mostly move back, to increase wing area, with minimum additional drag?

If in fact the scar resulted from initial impact and the flap was down some small amount, then the aileron may have been zero, or even roll left, (down).
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Old 10th Feb 2018, 15:48
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Originally Posted by G0ULI View Post
Standard aviation design notes suggest that the rudder be capable of resisting full aileron deflection on single engine aircraft or an outboard engine failure with other engines developing full takeoff power on multiengine aircraft at speeds 1.2 times the stall speed.

Either the Electra design was flawed in that respect, or the ailerons were or became deflected and held at considerably more than three degrees.
To counter the right wing down command, the rudder needs to move the nose left. In level flight this will roll the sim Electra over.

I've said that the problem was they were already in a bank when the problem was noticed. Below the speed at which a plane can do knife-edge flying, for any given speed there is some bank angle which is the maximum bank that the rudder can counter. The rudder needs to move the nose left, which in a bank has a vertical component. The sim tells me at about 160 knots the maximum right bank is near 60 degrees, meaning beyond that angle the rudder can't lift/left the nose. At that angle the plane can fly indefinitely. And when near that angle the rudder's authority is severely degraded.

I think they were calling for left rudder and the plane was balanced, if you will, near the peak of that curve. A little higher bank and the rudder would have lost all effect, they would have gone down much faster; a little lower and they would have recovered no problem. They were in the flatter part of the response curve, and it took some time for the nose to lift. Once it started to lift, like rolling down a slope, it gained speed. So I think they were rolling fairly quickly left when the right wing hit the embankment.

It wasn't an issue of bad design, in my [nonpilot] opinion, but bad luck that they didn't know of the problem until they were too far into the zone where the rudder authority is degraded. We've discussed this here previously, and I'm including it in my next release.
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Old 10th Feb 2018, 22:26
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Originally Posted by BRDuBois View Post
To counter the right wing down command, the rudder needs to move the nose left. In level flight this will roll the sim Electra over.

I've said that the problem was they were already in a bank when the problem was noticed. Below the speed at which a plane can do knife-edge flying, for any given speed there is some bank angle which is the maximum bank that the rudder can counter. The rudder needs to move the nose left, which in a bank has a vertical component. The sim tells me at about 160 knots the maximum right bank is near 60 degrees, meaning beyond that angle the rudder can't lift/left the nose. At that angle the plane can fly indefinitely. And when near that angle the rudder's authority is severely degraded.

I think they were calling for left rudder and the plane was balanced, if you will, near the peak of that curve. A little higher bank and the rudder would have lost all effect, they would have gone down much faster; a little lower and they would have recovered no problem. They were in the flatter part of the response curve, and it took some time for the nose to lift. Once it started to lift, like rolling down a slope, it gained speed. So I think they were rolling fairly quickly left when the right wing hit the embankment.

It wasn't an issue of bad design, in my [nonpilot] opinion, but bad luck that they didn't know of the problem until they were too far into the zone where the rudder authority is degraded. We've discussed this here previously, and I'm including it in my next release.
You will have noticed I make the case for the aircraft rolling left at embankment Impact?

“It wasn't an issue of bad design, in my [nonpilot] opinion, but bad luck that they didn't know of the problem until they were too far into the zone where the rudder authority is degraded. We've discussed this here previously, and I'm including it in my next release.”

I also feel comfortable to state they knew of the problem before they broke ground. The “turn” was way too early, the climb was almost flat, and they were committed to take off before a decision could be made to abort. The right turn was “noticed” by witnesses at eight thousand feet along, and 100 feet AGL.

The ailerons could have been jammed whilst taxiing to the runway, ailerons have no authority until 70 knots, so any notice of Roll would not have been sussed as aileron induced, likely Rudder was used to keep the centerline. Any roll prior to 200 AGL would have been countered by left input, the pilot would notice instantly no response in Roll, takeoff is accepted, and the rest is a litany of problem solving and trial. They tried to roll left before the aircraft broke ground, IMO. The steady state of Right Roll suggests that some left roll was available; with acceleration, the roll rate should have accelerated also with constant deflection, so aileron deflection was reducing as the flight progressed.

Any mention of aileron trim set at impact?
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