Help researching 1961 Electra crash

[BRDuBois]

Thanks, yes, the NTSB told me all the CAB files were turned over to the National Archives. The National Archives said the only CAB files they got on this incident were the final reports.

[BRDuBois]

I've uploaded a new version to http://we.tl/TvTrucG3Ak

This incorporates the material I found at the Chicago Tribune. It has a couple graphics to discuss the trajectory at the end of the flight.

Based on input here and from some emails I think my understanding of the situation has improved, and I'm characterizing the crash not as a failed attempt to make a belly landing, but more as an attempt to manage a descent that they couldn't stop.

This draft also has an explanation of the mechanism that can explain the leveling of the bank. The CAB discounted this, because they thought the bank was always increasing. Once the calculations showed that it couldn't always increase, suddenly this return-to-neutral makes much more sense.

[G0ULI]

Interesting.

I see you have incorporated some of the suggestions from the forum.

The only point of contention is that you seem to equate bank angle with a given rate of turn. While this in broadly true, it only applies in a balanced turn with ailerons and rudder acting together.

Given that there was no effective aileron control, the turn became progressively more unbalanced as the roll increased. So the aircraft was effectively skidding sideways through the air (in a horizontal axis).

That kind of makes a nonsense of any attempt to calculate a turn rate based on the angle of bank of the aircraft. That is to say, an aircraft in banked or even knife edge flight, may have no turning moment whatsoever. Or alternatively there may be a considerable initial rate of turn that then progressively reduces as bank angle increases, due to the ailerons and rudder becoming increasingly out of balance.

That would account for the impact site being where it was, despite calculations suggesting that this would not have been possible with progressively increasing bank angle and rate or turn. The rate of turn didn't increase linearly with increasing bank angle. In fact it may well have reduced somewhat.

[BRDuBois]

I see you have incorporated some of the suggestions from the forum.

Of course. That's what I came here for. I've also been in email discussions with pilots.

Yes, I understand the turn and bank calculations can be off, and I don't yet know how much off. I need to play with a simulator. So for the time being this is an approximation.

[BRDuBois]

New version posted at https://we.tl/beXUsgYPvX

Two significant additions to this release.

The first is discussion of an Argentine Navy Electra crash in '89. Video is available at

You Tube

The video shows what an Electra actually does in a high bank right wing impact, compared to what the CAB said of Flight 706. I use a bunch of frame grabs to show how this contrasts with Flight 706 regarding trajectory, crash dynamics, and survivability. Very useful lessons.

The second is a series of posed images to show what N137US would have looked like in different bank angles. My most encouraging supporter (a retired NWA pilot) gave me a big metal Electra model, and I posed it on a stand to replicate perspectives. The most important is the view from the control tower, presented as a storyboard in correct scale.

[G0ULI]

The Argentinian accident invites a lot of interesting comparisons with the original crash. The scale representations of the aircraft as it would appear in flight are a great idea. It is possible to appreciate how difficult it is to estimate bank angle from any significant distance and without a clearly defined reference. Well done.

I am still uneasy at your criticism of the original accident reports. The investigators at the time identified a disconnected aileron cable as the component commanding full right wing down. The aircraft was effectively uncontrollable from this point onwards, so no matter what action the flight crew performed, the crash was inevitable.

It is possible to run thousands of different scenarios through a modern computer and come up with several possible solutions to explain how the aircraft ended up at the final crash position and with the wreckage arranged as found. At the time of the accident, such tools simply didn't exist and imvestigators were forced to rely on experience and rules of thumb to arrive at a conclusion.

So while your scenario may indeed be more accurate in terms of describing the flight path and sequence of events during impact, it doesn't actually serve to improve flight safety, which is the primary purpose of any accident investgation.

I continue to have no doubts whatsoever that the flight crew on that day did everything they could to save the aircraft, but the physical evidence, photographs and contemporary reports do not indicate a nearly successful attempt at belly landing.

That is my interpretation of the evidence, yours is different and backed up by computer modelling and comparison to other incidents. I am happy to accept that what you propose is a possibility but not the most likely probability as to the exact sequence of events.

You have collected a mass of data from various sources and you are now probably the best informed person on the planet with regards to this accident. You are entitled to express your opinion as an expert after all that research and to be taken seriously. The experts who investigated the accident at the time were also doing their best but with the added constraint of needing to find the cause as soon as possible and without the benefit of modern technology. The truth probably lies between both sets of conclusions.

I shall be studying your latest report in more depth over the coming weeks.

[G0ULI]

I'm impressed that they all got out alive from that crash. What is clear is that there was a lot of disturbance of the wreckage during the search and freeing of casualties. The same is probably true for most crashes where there might be the possibility of survivors. That makes any reconstruction of the incident more difficult for investigators.

Where I saw a possible similarity is in initial contact by a wing with the ground. Also the increasing angle as the aircraft climbed out from the runway and control was lost.

While it might not be possible to make direct comparisons between the two crashes, the video gives an indication of the sorts of time scales involved and what a witness to the original crash might have seen.

Other than that, I agree with you megan.

[BRDuBois]

G0ULI, you're correct that my fault-finding has nothing to do with the cause of the crash. Megan had made the same point earlier. But my whole subject is the impact sequence, and I explicitly say that I don't question the cause of the crash. With regard to that part of the investigation I have nothing to criticize.

My subject is the impact sequence and plane attitude, which was investigated so badly as to qualify for my term "slapdash". If I seem harsh, it's because I lived through that and watched others live through it as information trickled in. There were many people who cared very much what happened. After over 50 years we can see that the news we waited for was misreported badly. It makes me indignant, I confess.

I've adjusted my phrasing and my understanding, based on quite a few conversations with pilots. In the document I now characterize it as not so much an attempt to make a belly landing as an attempt to manage a descent. With more altitude they might have had much better results. They were headed for the ground and were hoping not to hit too hard, rather than having the goal of putting it on the ground.

I'd be delighted if someone had the computational tools to re-enact the possibilities and see how it plays out. I don't have the equipment for it. As I say in the document, I can show that the CAB/ALPA reports are wrong, but I can't prove that I'm right. I'm confident of being pretty close, but that's about it.

A couple pilots have discussed the flight with me. They agree that this maneuver would never be tried at all (at a safer height) and there will be no data on it or first person reports. They suggest I try a flight simulator and see what results I get, and I've started on that project.

I presented the Argentine crash not because it was like the Chicago crash, but because it's like the CAB said the Chicago impact started but the Argentine crash played out differently from the first impact. No two crashes are going to be alike, but finding this one gives us the chance to draw a couple lessons from it.

I agree that the crew did all they could, and we knew that since '61. I get a lot of drive-by psychoanalysis out of this. People think I'm trying to salvage reputations that don't need salvaging, or trying to deal with trauma that I was over at least 30 years ago.

Being the best-informed person on the planet on this particular crash is setting a fairly low bar, considering that everyone who studied it in person is probably dead. I'd rather be known for my book The Passionate Ape.

[BRDuBois]

Hi Megan, glad you're still here. I have valued your input on this thread. Thanks for the video link.

As I said, the Argentine crash is not a match for the Chicago crash. The similarity starts and ends with the right wing impact.

But three things can be taken away from the Argentine crash: The trajectory of a plane with no lift, the rotational effect on an Electra when the right wing hits, and the survivability of a moderately low-angle Electra impact. These are all highly relevant to understanding the dynamics of the Chicago crash and how close they came to a survivable incident.

ETA: Your video has much better quality. The clip I found was passed through some steadying software and was electronically zoomed, and lost a lot of detail. I'll be able to redo my graphics with better quality next release.

[BRDuBois]

Oh yeah, that's a major reason why the Argentine crash is so interesting. N137US ended up tail-first and upside-down, and the Argentine plane ended tail-first and right side up.

It seems highly likely that the CAB investigators had in mind something like the Argentine impact sequence when they viewed the wreckage. It sort of fits the description of cartwheel, in a sloppy way. And the tail section being upside-down apparently didn't faze them. But being upside-down is the kiss of death to their model, because it means N137US arrived at the final site with high energy and nose-first, and then flipped over.

I presented the Argentine crash for contrast, not to show the similarity. The Argentine plane crashed just how the CAB said N137US crashed, but the Argentine plane behaved in a completely different manner. That's why (as I said in my document) the Argentine crash refutes the CAB model. If N137US crashed as the CAB said, a backward slide would be normal. But being upside-down, N137US obviously didn't crash that way.

Do you see the implication?

ETA: One of my pilot friends read the CAB report and busted out laughing at the description. He said "so it hit the right wing, and then defied the laws of physics for 800 feet."

[BRDuBois]

Several pilots have said that any information about the flight dynamics will have to come from a simulator. I've loaded X-Plane, which is the best one for my purposes, and am using a L188C model written by David Starling. The manual says the Electra at the conditions for Flight 706 should stall about 110 knots, and the model does. The maintenance manual says the rudder can deflect 30 degrees right and 25 left, and the model has it exactly.

The model appears to be an accurate representation, and we can probably take its behavior to be correct within a smallish percentage of error. I'd be interested in hearing from pilots about the feel of the model.

One of the questions is whether an Electra can knife-edge fly. Turns out it can at any speed over about 250 knots. At lower speeds there isn't enough airflow over the rudder to get the nose up. I've run a number of tests, all starting at 1k feet over Puget Sound, since Flight 706 got to 300 feet tops and ORD elevation is 680 feet. My tests start at 160, 200, 250 and 300 knots, and I throttle up as needed as soon as the bank goes vertical. At 160 knots the plane has no chance, and is essentially in free-fall for the first 500 feet. At a starting 200 knots after a few tries I could get to 250 knots about 50 to 150 feet over the water. Starting at 250 or faster the plane had no trouble at all.

There will be some discussion of this in the next version. The answer for now is that knife-edge flying was not possible for Flight 706 because it was about 100 knots too slow.

My next step is to write a program harness for X-Plane so I can run turn and bank trials and collect more rigorous numbers. The questions to address are (1) what bank can the rudder induce, or what unwanted bank can it counter, and (2) what do rudder inputs do to turn radius calculations.

Hand-flying suggests that the rudder alone can turn the plane completely over, which impressed me. I'll be interested in seeing how the data turns out.

[G0ULI]

Excellent idea to get a feel for how the aircraft handled and the effectiveness of the rudder. Even though sustained knife edge flight is not possible at speeds below 250 knots, the rate of descent is presumably reduced somewhat, even at the slower airspeeds? Inappropriate use of rudder can certainly turn an aircraft inverted and/or induce a spin.

[BRDuBois]

I'm certain that there's at least some lift from the side of the fuselage, but I haven't measured the exact rate of descent to determine how much. I hope to do that when I develop some firmer numbers. My first goal is to program the harness for running the simulator, and that is unfortunately a little ways away due to competing demands for my time.

[BRDuBois]

Other commitments have taken me away from this project for the last month. I don't yet have the program harness working. Programming is my field, and I understand the problem, but don't have a solution yet.

Meanwhile I've been trying to get some useful information out of the simulator. Bear in mind that the simulator results are all that's available, but they can only be considered an approximation. I covered the fact that knife-edge flying is not possible at 160 knots. Two other questions are answerable by hand-flying: What are the behavior characteristics of an Electra banking right under full left rudder, and what attitude would result in a five degree descent slope.

Several pilots have agreed that the rudder must have been hard left. This would be an instinctive response, it would have an immediate effect, and they would have maintained it until they regained level flight. So we have an airspeed of about 160 knots and hard left rudder in a right bank. The first issue is to determine what this does to the turn radius. All my illustrations are based on balanced turns, because no one could estimate what the rudder inputs would do to the radius.

We have evidence that the bank angle at impact was near 34 degrees, so I used that angle when collecting a representative radius value, but I'm not saying this radius calc is itself evidence for a 34 degree bank. A balanced turn at 160 knots and 34 degrees gives a turn radius of 3370 feet. A 35 degree bank at 160 knots and hard left rudder in the simulator gives a turn radius of 5275 feet. I'll be running more trials to get an average, but it's in this ballpark. The left-rudder turn radius is around 1.5 times that of a balanced 35 degree turn, give or take.

In my illustration on page 20 of the 160602 document, I said that the red-dotted path was the most extreme possible, but that was based on a balanced turn. That path would have resulted in an impact bank angle of about 22 degrees, which made it unrealistic. Given the new unbalanced turn radius estimate, that path becomes much more reasonable. The plane could have reached the 271 heading with considerably more bank than 22 degrees. So the initial emergency probably started with a higher bank farther southeast than I had thought.

The second question is: What attitude would result in a 5 degree descent slope. At 160 knots a 90 degree bank results in free-fall, as discussed earlier. When this project showed me that they weren't in a 90 degree bank as reported, I wondered why they didn't climb. The simulator says at a 34 degree bank and 160 knots with hard left rudder it's easy to climb. So I'm looking for a bank angle extreme enough that the plane has insufficient lift to stay up, but not yet stalling.

As the bank increases, the elevator angle has less and less effect vertically, and starts to serve only to tighten the turn. Meanwhile the rudder has more responsibility for keeping the nose up, but it's going too slow to do that. N137US weighed 93,000 lbs and would have stalled at about 63 degrees in a balanced turn at 160 knots. My numbers are rough, but it appears that the simulator is giving stall warnings just above 55 degrees. Pulling back on the yoke increases the stall likelihood by lifting the nose, while not pulling back keeps the plane descending.

The exact rate of descent is highly sensitive to airspeed and bank angle, but a descent of 1400 to 2000 feet per minute seems within reach. The 5 degree slope Lockheed estimated would be 1400 feet per minute. The simulator run suggests they were at the stall boundary and unable to stop descending. My latest report characterizes their effort as just trying to manage an unstoppable descent, but seeing the stall warning makes it clearer.

This view, rough as the numbers are, is the best evidence I've seen that my 34 degree impact bank angle estimate is too low. This gives about a 20 degree gap between the simulator's result of a maximum 55 degree bank in flight and physical evidence of a mid-30 bank at impact. I can see a couple possibilities. One is that the flight bank and impact bank are both somewhere in the middle, and computation errors in the simulator are showing a steeper bank than they actually could have had.

The other is that in the last two or three seconds the bank angle was changing, perhaps as the aileron boost unit was returning to neutral. If the second one is the case, then the turn radius was decreasing and the elevators would have been able to pull the nose up. In other words, it's possible the impact was actually a flare that they were unable to initiate until too late.

The idea that the bank was changing rapidly in the last couple seconds feels conceptually awkward, a bit too close to magical thinking. I'm inclined to think the first possibility is the better one.

The rate-of-descent data is very rough because I have a really tight window to get into position and collect data, and I'm no pilot. I wasn't able to collect turn radius data at this extreme bank. If I can get the harness working it will give better numbers.

Meanwhile, I'm always interested in feedback.

[BRDuBois]

I've uploaded a proof-of-concept video to my weTransfer page. This is intended to show the kind of data I'll capture using the X-Plane simulator. This is a 15 mb MP4 video. The frame rate is low, but the goal here is to capture data, not to make a smooth video experience. https://we.tl/GU7wQaiDOZ

I envisioned three levels of testing with the simulator. The first was to test basic handling characteristics of an Electra. One of the objections raised to my analysis has been the proposal that Flight 706 not in a shallow bank but was knife-edge flying when it hit, and this explains the slow descent. Hand-flying the simulator shows that this is impossible because Flight 706 was going about 100 knots too slow for knife-edge flying. Hand-flying is sufficient for this proof, but that's about my limit as a pilot.

The second is to determine the characteristics of an Electra in a banked turn. Turn radius is critical to understanding how Flight 706 got to where it impacted on the airport grounds, and the angle of attack it could have had. So the next set of tests involves putting the simulated plane into turns of varying angles and different rudder deflections and measuring the turn radius of each. A pre-requisite was to write a simulator-controlling harness, which now is showing basic functionality. The first job in this test series is to calibrate the simulator and ensure that it accurately reflects what we could expect of an Electra. The link shows part of such a calibration step.

Non-Techies skip this part: The internal control is via a Lua plugin running inside Gizmo. Gizmo is a Lua/X-Plane interface plugin. This Lua script is a dumb plugin; it passes simulator data (eztracted by Gizmo) to the external program and the external program passes data values for the plugin to stuff into the sim through Gizmo. The plugin makes no decisions. The external program is a Delphi 10 (Pascal) program that has rudimentary flying abilities. Delphi 5 was my last installed version, and it's the best IDE I ever used, but it's unable to deal with W10. Embarcadero is giving away an intro-level Delphi 10 for free for the next four or five days, so it you ever want it this is a great opportunity. The intro level has plenty horsepower for this job.

The uploaded video shows the level of control needed to establish Electra flight characteristics. The harness can hold the sim plane within about a half a degree of bank angle, and within very few meters of height. There is a ringing effect, so the longer it runs the smoother it gets. With this harness I can put the plane into a stable state and then mess with rudder inputs and the like. The large readout shows the time it takes to make a circle, control surface deflections, headings, etc. It's not all wired up yet. The goal at this point is to calibrate the simulator and refine the Delphi flight controller so it smoothes more quickly. The video shows the Electra (in 1960's livery) circling over Elliot Bay and Bainbridge Island.

Not shown in the readout are the longitude and latitude values that determine exact coordinates. These are captured in a log file with other data, and I use those to compare to the speed and timing, which determines circumference, to check on the circle dimensions. There is a distortion in these measurements due to the way the simulator handles the 'flat earth problem', so I'll have to do the real measurement flights in Jakarta, not Seattle. Circles flown near Seattle turn out to be north-south-elongated ellipses, buit circles flown near the equator are circles.

The third set of tests will be to replicate possible flight paths for Flight 706. I won't be able to work on this until I have more data, a feel for how the sim handles, and a better Delphi flight controller. If the sim cannot be shown to be a good representation of Electra handling, then more work would be wasted. Even if the sim is only a marginal flight model, there should be some useful information about how rudder deflections alter the turn radius. If the sim turns out to have a dependable flight model, then there may be more useful data forthcoming. At this point I can't be sure the sim will generate anything useful beyond disproving the knife-edge flying conjecture.

[G0ULI]

All good stuff. Obviously you need to concentrate on one set of data at a time to establish the correct control responses. Don't forget to consider the effect of various engine power and propeller pitch settings once you have your basic data established. For initial analysis, assuming the engines were developing full power at lift off would be reasonable, but changes to engine power settings may have been made as the bank developed. This would change the airflow and therefore the effectiveness of the flight control surfaces on the wings and tail. If you don't get reasonable results from your initial simulations, this may prove to be the cause of the problem.

[BRDuBois]

I've put five videos on Youtube, illustrating flight dynamics for an Electra using the X-Plane simulator.

https://youtu.be/2JiGSJ5xPQg shows knife-edge flying, which was proposed as an explanation for the slow descent of N137US. It shows it at about 250 knots and about 150, which was the actual speed of Dad's plane. This is the only clip where I hand-flew the plane. The rest were all run by my harness, for consistency and repeatability.

https://youtu.be/kwVrHJ1obSk shows how I validated the simulator's turning circle calculations. Turn radius accuracy is critical in using the simulator for this research. I ran the plane in circles at bank angles from 10 to 35 degrees and varying speeds and heights. At each setting I ran five or more circles and averaged them for accuracy. The time required for each circle, along with the speed, gives me the circumference and therefore the radius. The bank angle and speed gives me the radius using the standard formula. The extremes of latitude and longitude gives the diameter and therefore the radius. These all agree to a high degree of accuracy. The elongation of circles at a distance from the equator turns out to be a computational pleat used by the simulator to cope with the "flat earth" problem, and has no effect on the short distances involved in my Flight 706 reconstruction.

https://youtu.be/62nRO2VFyGM shows the planned departure of Flight 706, with a gradual turn toward the west. This is shown for contrast with other videos, and describes where the turn starts in relation to the tower and runway.

https://youtu.be/R3ytdwRsxUM shows the increasing bank described in the CAB and ALPA reports, and shows what the result would be of such a bank. All the trial runs end at least 2,000 feet from the known impact point, and none of the runs ends in a 90 degree bank. These runs presume that the ailerons remain at the deflection used to initiate a smooth turn somewhat less emphatic than a standard rate turn.

https://youtu.be/9z_zaW5MvOU shows what it takes to achieve the 90 degree bank described in the CAB and ALPA reports. All these trials end from 2,700 to over 3,000 feet from the known impact point, and their final heading is 90 degrees off from what was surveyed.

I am tagging all these videos with N137US, which is not otherwise used on Youtube. When Youtube gets their indexes updated, that search term should bring up all these.

I have two more sets of simulation runs in mind. One is to explore what would be required for the plane to end in a 90-degree bank at the 4,000 foot distance. The other is to recreate what I think Dad's plane did. Based on the simulation results so far, it appears possible that I'll be able to propose a causal factor that has not been mentioned before. It will be very interesting to see whether this pans out.

[G0ULI]

One thing that occurs to me while watching your videos is that the ailerons are functional throughout the simulation run. You can vary the aileron inputs to attempt to duplicate the actual flight path taken by the original accident aircraft, but does that actually represent the true aileron positions during the accident flight?

Once the aileron drive cable broke, the ailerons may have been held in a fixed position for a time by powered assistance until the pressure bled away or the power boost was turned off. Alternatively, the ailerons may have moved due to airflow over the wing and prop wash from the engines.

Because of this, it is difficult to conclude that the turning circle was continuous or at a constantly and steadily increasing bank angle. Clearly the aircraft banked to the right after take off and that bank increased to a point where the aircraft could no longer remain in the air. There is the possibility that the bank angle increased in a series of 'jumps' as the crew struggled to regain control and as the aileron deflection altered due to crew inputs such as turning off powered assistance and changing airflow patterns over the wing.

Rather than assuming a steadily and smoothly incresing bank angle, you might want to try increasing the bank in a series of steps that might correspond to attempts to regain directional control.

The initial cable break would require a left rudder deflection to try and correct the bank. The ailerons would progressively become more susceptible to aerodynamic forces, and propwash effects as engine power levels were adjusted and the bank angle increased.

It seems clear from your tests so far that this wasn't a nice neat curving climb and descent with a steadily increasing bank. You have already concluded that this simply wasn't possible if the aircraft was to finish up at the actual crash site.

Perhaps a take off with a gentle 5° bank which then increases steadily to perhaps 30° bank at the highest point in the flight, followed by a jump to 45° increasing to 60° over perhaps 5-10 seconds, then a further roll to 70+ degrees to the impact point. I feel this would more accurately reflect the possible flight profile and allow the turning radius to agree with the results recorded in the accident investigation as to impact point in relation to the runway and airfield.

The problem is that once the aileron cable broke, it is very difficult to establish the position of the ailerons between that point and the moment of impact, when witness marks would reveal the deflections with reference to the wings. Did the ailerons remain in one fixed position, did they flutter in the slipstream, were they influenced by the engine power settings, or did they move in response to control power boost devices being cycled off and on, perhaps repeatedly?

Considering the flight as a series of step changes which temporarily mitigated the situation, but then failed is probably the way to go in understanding this accident.

[BRDuBois]

Well, I CAN alter the aileron settings, but I don't. Once the turn is initiated I leave the ailerons in that position for the remainder. I use a variety of settings in different runs, but it's stable within each run. There's a little jiggling out past the second decimal, but that's generated by the sim and I can't control it. For this series of tests and examples, I'm presuming the ailerons aren't moving after the cable parted. I've been doing some other runs using a scenario where the ailerons return to neutral, but no useful results yet.

It's possible the ailerons were moving significantly after the break. In order to test possibilities, I need a backstory to justify the exploration. I can't presume they were moving at random and find all the outcomes. Statistically such research is impossible because the permutations are endless. Logically it becomes meaningless because I could concoct any movements I like in order to bolster my case.

If there's a solution (and there's no guarantee I'll find one) it needs a rational scenario for a framework. The system returning to neutral is one. The idea that they were doing something that resulted in some sudden movements is interesting, but I'm not sure how to approach it. The most accessible premise is that there was no movement, since the deflection noted in witness marks is a reasonable deflection to start a moderate turn.

Take a look at https://www.youtube.com/watch?v=MDc4fHJFchY

That's a demo I did to illustrate ideas in an email thread I've got going with a couple pilots. I've been exploring the reaction when the left rudder is initiated at different points after the cable failure using different rates of change and different degrees of aileron deflection. I'm not getting satisfactory results, but it's getting closer.

I've been doing some experiments with hand-flying the simulator in high-angle banks with hard left rudder, to see how it behaves and to see at what point it can't maintain altitude. It's possible that the real answer lies in a higher bank than I'd previously considered, maybe in the mid-50 range, with a rapid left rotation on first impact.

The damage geometry says the plane was banked no more than the mid-30's when the prop left scars on the embankment, but the embankment actually had several strikes. I'm impressed with how fast the plane rotates counter clockwise about its longitudinal axis and right about its vertical axis when it hits the right wing a glancing blow, and then straightens again under rudder influence. Perhaps the answer is that it hit the embankment at a mid-50 bank, and left prop marks while in a mid-30 posture within a matter of a few dozen feet.

I don't know how much weight we can put on impact behavior in the sim, since it's a flight sim and not a crash sim. It's very doubtful that we can trust the plane model to accurately reflect the effect on the plane from tearing off half a wing.

[G0ULI]

The videos certainly demonstrate that flight is considerably prolonged with the application of left rudder to counteract aileron deflection.

The question of the aileron positions during flight can perhaps be simplified somewhat by considering that the aircraft maintained a constant turn to the right. This suggests that the aileron position at the point the cable broke was at the very least maintained.

Application of left rudder failed to rectify the situation, so on the balance of probability, the ailerons appear to have moved somehow to a position where they became even more effective at rolling the aircraft despite the application of full left rudder. The aircraft would have been flying in an unbalanced sideslip. Would the disrupted airflow over the wings have been enough to move the ailerons, sucking them further from a neutral position?

It is probable that the engines on the right wing would have had the power pulled back at some point in order to try and get the wing to drop. The left engines would be left at full power to try and prevent an incipient spin developing which would have led to an immediate crash.

As you say, the closer you look at all the variables and interactions that could have been involved, the more difficult the problem becomes in arriving at a credible solution, rather than one that just happens to fit.

This is why I suggest that the flight needs to be considered as a series of events with the aircraft reacting to the failure and the crew's attempts to corect the problem.

Aircraft takes off a bit long and low on the runway, not necessarily a problem.
Aircraft begins a standard banked departure turn.
Aircraft climbs in a banked turn.
Aileron cable breaks.
Crew are unable to adjust the angle of bank using ailerons.
Bank increases.
Up elevator commanded to maintain height?
Progressive application of left rudder to the limits.
Further movement of aileron due to disrupted airflow over the wings in sideslip?
Aircraft starts to descend.
Crew reduce engine power to right wing engines, maintain full power on the left.
Does the application of differential engine power move the ailerons still further out of the neutral position and increase the bank angle?
Aircraft continues to roll and descend.

I have a hunch that doing the right thing in reducing engine power on the starboard engines while leaving the port engines in full power may have resulted in the ailerons being moved out into a more effective, rather than reducing to a neutral, position in the slipstream. Flight training would have taught that applying more power to the port (left) wing should raise the wing and turn the aircraft to the right. So while the flight crew reacted correctly and in accordance with their training and experience, it is possible that the "correct" course of action would have been to completely and counter intuitively reduce engine power, particularly on the port wing first. This would inevitably have resulted in a crash landing, but just possibly in a more wings level attitude.

As I say, this is just purely supposition and it is possible that the crew did finally take a counter intuitive approach to control of rhe aircraft when it became obvious that a crash was inevitable. That could certainly account for the apparent reduction in bank angle before the initial impact, which is what you have been trying to explain all along if I have my facts straight.

I doubt that these possible elevator control inputs, aileron positions, engine power settings and rudder inputs can be duplicated using personal computer flight simulation software, but approximations can be made to test the ideas. As you have already demonstrated, just applying a hard rudder against increasing bank angle dramatically prolongs the flight.

I think you are making genuine progress in explaining what actually may have happened. You are certainly building a fairly strong case that tends to support and explain your version of events.

I don't think the accident investigators at the time were at fault in any way. They had to work with the resouces available to them at the time and no doubt with considerable commercial and government pressure to produce a result quickly.

You have the benefit of being able to review and model potential scenarios over and over without any constraints. I would be surprised if you don't eventually arrive at a better solution to this tragedy, one that demonstrates that your theory is correct and also agrees with the results recorded at the time, if not the conclusions.