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Old 1st Jan 2018, 16:33   #301 (permalink)
 
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Originally Posted by cordwainer View Post
Thanks, this and your other details understood, appreciate the clarification.

So am I understanding correctly that the plane would have had to spin around and head forward briefly in order to flip into its final orientation? If so, isn't this quite possible given the marshy ground (possible hydroplaning allowing it to spin around more easily), plus the multiple explosions noted by witnesses prior to the later tail explosion?
Marshy ground. That would support my theory. Not “spinning around”, laterally, but flipped, vertically, arse about.

Skidding forward, upright, leading edge on, the main spar and the wheels entered the “ditch”, and stuck. Dragging a loosely attached tail section, the assembly flipped over, to land as we see it. Tail attached, very loosely, but connected via the keel beams.

At this point, what was left of fuel, (which Lockheed designed to be contained entirely in the wing), flooded the tail section, puddles under the wing, and lit.

Respectfully,

concours
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Old 1st Jan 2018, 16:44   #302 (permalink)
 
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Originally Posted by BRDuBois View Post
Yes, this might have happened. I discussed how it might have bounced forward in my document. In some fashion it had to be pointing forward. Point being, this means the CAB assertion that it slid backward is wrong, and until that is recognized it's impossible to grapple with the puzzle. Again, this is not a moral judgment about the CAB but a statement of fact. There's something wrong in how the CAB reported it.

This is not about gleefully pointing out that the CAB investigators were a bunch of idiots. There is a major error in this minor aspect of the investigation, and it raises a puzzle. So the questions are: How did the plane get into that position? What else (if anything) did the CAB get wrong?

If you reverse-engineer the plane's arrival at the final site, you start to see a very different impact scenario.
Only to add support to what looks like the preferred theory, mind that the tail section was attached to the wings throughout, via the keel beams. We know this because both assemblies came to rest together, though not correctly aligned.

The tail follows the airplane, always, in flight, and even here, in its demise. Not solidly attached by any means, but connected nonetheless. Imagine the tail wagging, as in dog’s tail, as it slid to its rest.

Your explanation is elegant, and enhances what is most likely the probable path.

Great respect,

concours
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Old 1st Jan 2018, 17:41   #303 (permalink)
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Originally Posted by Concours77 View Post
both assemblies came to rest together, though not correctly aligned.
I suspect they were completely connected, and collapsed in slightly different orientations when the fuselage burned through.
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Old 1st Jan 2018, 21:24   #304 (permalink)
 
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Originally Posted by BRDuBois View Post
I suspect they were completely connected, and collapsed in slightly different orientations when the fuselage burned through.
precisely.

Only to add that if tail/wing stopped while fully connected and in proper structural alignment, the fuel mist explosion in the fuselage (tail) section would have met resistance at the dorsal, more robust area than the sides. Such an asymmetrical release of explosive gases would have rotated the tail and twisted it into the orientation we see in the photo....hat tip to cordwainer!
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Old 2nd Jan 2018, 01:52   #305 (permalink)
 
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what telltales, what chronology? Was it used to support the “vertical bank” theory at first impact? (Right wing at Railroad Tracks)? Was its inclusion to support the first impact, or the second?
I wish you would read and digest the report, it says,
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The Captains artificial horizon indicated that it was receiving a signal of 90 to 100 degrees at the time it ceased to function
The narrative makes plain it was the second impact, when the cockpit area was destroyed, not the embankment impact.
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Old 2nd Jan 2018, 02:16   #306 (permalink)
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Originally Posted by Concours77 View Post
Only to add that if tail/wing stopped while fully connected and in proper structural alignment, the fuel mist explosion in the fuselage (tail) section would have met resistance at the dorsal, more robust area than the sides. Such an asymmetrical release of explosive gases would have rotated the tail and twisted it into the orientation we see in the photo.
I doubt that we can make this connection. We don't know if it impacted as a flip-over, which would be minimal spray, or coming down from some height as in my missing-forward-fuselage sim run which might give a considerable spray. And whether the conjectured fuel-air explosion would move the empennage is a guess too far, seems to me.

Far as I can see, accepting the CAB description means envisioning the aft section essentially sliding to a stop and then bursting into flames. Once you realize that it can't have been sliding backward, the questions multiply and the certainty drops.
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Old 2nd Jan 2018, 02:29   #307 (permalink)
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I wish you would read and digest the report, it says
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The Captains artificial horizon indicated that it was receiving a signal of 90 to 100 degrees at the time it ceased to function
I have no clue what an artificial horizon might read if the plane is in a violent right-turn about its vertical axis. Presumably this depends on the technology of the time.
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Old 2nd Jan 2018, 11:55   #308 (permalink)


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The older type vacuum-driven attitude indicators have bank limits of approximately 100° to 110°, and pitch limits of 60° to 70°. These limits are imposed by the mechanical construction of the gyroscope. Modern designs frequently exceed these limits.

Electrically driven gyros can be designed to display 360° movement in any axis.
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Old 2nd Jan 2018, 15:04   #309 (permalink)
 
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Originally Posted by G0ULI View Post
The older type vacuum-driven attitude indicators have bank limits of approximately 100° to 110°, and pitch limits of 60° to 70°. These limits are imposed by the mechanical construction of the gyroscope. Modern designs frequently exceed these limits.

Electrically driven gyros can be designed to display 360° movement in any axis.
Limits are important, but not germane. What would be more instructive would be “lag” (response) of the instrument in dynamic maneuvering...

My exception would be using the instrument’s reading at impact to support (or defeat) a “conclusion” of attitude at RR impact....we are left with the photo of the embankment, and wildly discrepant witness testimony.

So. Why would CAB report “when it ceased functioning” instead of reporting “at second impact”? Is that the case? It leaves open a conclusion that it was somehow relevant to a discussion of initial impact. Sloppy.

It also opens the discussion of bias. When did the boost unit “cease functioning?” We are given a conclusion that it was damaged by fire, a rather obvious statement, but it biases the readers to a conclusion that fire alone damaged the boost unit, after impact.
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Old 2nd Jan 2018, 16:21   #310 (permalink)


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It is standard practice to estimate instrument readings from the faint indentations left in the dial face at the moment of impact. The wing contact with the railroad embankment was unlikely to have been severe enough to produce such a mark. We are left to conclude that the second impact with the ground that detatched the nose section was the one that produced the witness marks used to estimate the aircraft attitude at that point.

It is very tempting to try and read between the lines and second guess the investigators, especially when an element of doubt has been raised about certain aspects of the report. I prefer to believe the report should be read without trying to put a modern interpretation on the wording. It is clear the investigators at the time knew what they were doing.

What I find incredible is the accuracy with which cables in the control runs were expected to be assembled and installed. Cable runs of hundreds of inches were expected to terminated and fastened to tolerances measured in hundredths of an inch or better than one part in ten thousand. The aircraft was originally built with the precision of a Swiss watch, an incredible technological achievement. Despite the disruption, the investigators were still able to draw meaningful conclusions from the wreckage.
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Old 2nd Jan 2018, 17:17   #311 (permalink)
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The CAB mentions "The relatively slow, progressive disintegration which occurred in this accident makes it impossible to assess the in-flight significance of instrument readings which might otherwise be reliable."

Page 104 of my last release, as a footnote.
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Old 2nd Jan 2018, 17:54   #312 (permalink)
 
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Originally Posted by G0ULI View Post
It is standard practice to estimate instrument readings from the faint indentations left in the dial face at the moment of impact. The wing contact with the railroad embankment was unlikely to have been severe enough to produce such a mark. We are left to conclude that the second impact with the ground that detatched the nose section was the one that produced the witness marks used to estimate the aircraft attitude at that point.

It is very tempting to try and read between the lines and second guess the investigators, especially when an element of doubt has been raised about certain aspects of the report. I prefer to believe the report should be read without trying to put a modern interpretation on the wording. It is clear the investigators at the time knew what they were doing.

What I find incredible is the accuracy with which cables in the control runs were expected to be assembled and installed. Cable runs of hundreds of inches were expected to terminated and fastened to tolerances measured in hundredths of an inch or better than one part in ten thousand. The aircraft was originally built with the precision of a Swiss watch, an incredible technological achievement. Despite the disruption, the investigators were still able to draw meaningful conclusions from the wreckage.
Thanks Gouli, a patient and thoughtful message for all.

I have been considering the quality of construction myself. Impressive. The long cable runs terminating in four inches of a connection devised by daVinci, threads.

To be accurate, it is not the cables that adjust to tension, they are finite in length, and subject only to variations in temperature, in Lockclad, even the temperature deviation is mitigated by the locking aluminum sheath around the stainless stranded cable.

The 4.2 inch stainless threaded couplers and brass junction blocks were the culprits.

When considering the precision in cabling, one wonders why the cables were not simply thimbled, and held in place by safetied bolts.

Tension could be adjusted with deflection in the cable, without the need for “safety wire”.
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Old 2nd Jan 2018, 18:14   #313 (permalink)
 
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What would be more instructive would be “lag” (response) of the instrument in dynamic maneuvering..
There is no lag.
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It leaves open a conclusion that it was somehow relevant to a discussion of initial impact. Sloppy
No it doesn't. What is sloppy is the displayed inability to understand what is written and its import, and you have the hide and audacity to denigrate the CAB.
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When did the boost unit “cease functioning?”
The unit ceased functioning when the crew disengaged it, but it had already been rendered useless by the parted cable in any event.
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Cable runs of hundreds of inches were expected to terminated and fastened to tolerances measured in hundredths of an inch
No. The cable will have a length spelled out in the maintenance manual and the accuracy of the length is not subject to sub millimetre accuracy. Minor differences in length are taken up by turn buckles, or like fittings, which are tightened to a particular cable tension, with the tension applied corrected for temperature. The slack absorber allowed a total of .7 inch adjustment, and in addition there would be another adjustment tolerance available at the cockpit turn buckle. You would be surprised at the plethora of wire cables in a 747, or even 737.
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The relatively slow, progressive disintegration which occurred in this accident makes it impossible to assess the in-flight significance of instrument readings which might otherwise be reliable
The report makes no such statement. I can only guess you are referring to the flight recorder.
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The 4.2 inch stainless threaded couplers and brass junction blocks were the culprits
No. the only culprit was the failure to safety wire the unit. Standard aircraft engineering practice and design which has worked for a century.
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Old 2nd Jan 2018, 19:20   #314 (permalink)
 
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By my count, you “quote” three separate posters. You might consider separating my ignorance from the other two. Sloppy.

You seem to have no problem stating as irrefutable fact that which the CAB calls “probable”

I like that in a pilot....
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Old 2nd Jan 2018, 19:30   #315 (permalink)
 
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You might consider separating my ignorance from the other two. Sloppy.
Not sloppy at all, I would expect the authors to know what it was they wrote.
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You seem to have no problem stating as irrefutable fact that which the CAB calls “probable”
And what was that pray tell?
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Old 2nd Jan 2018, 20:29   #316 (permalink)
 
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Not sloppy at all, I would expect the authors to know what it was they wrote.And what was that pray tell?
The authors, yes, but that leaves the rest of everybody not sure.

“Probable Cause”.

You are “probably” correct, though you leave no room for questions. CAB is not a sacred source of truth.

Is it possible the Boost unit was malfunctioning to any extent pre take off?
Absolutely. The squawk sheet on N137US’ aileron system prior to boost unit replacement was extensive.

Could the problem have extended beyond simple boost replacement? Be careful, now you need to involve NWA maintenance in your “irrefutable”.

Crimped sheaves? Cracked connectors? Badly bled hydraulics? Leaky cylinder? Incorrect fluid? The list is legion.

My questions of the report are no more insulting to CAB than your irreverent demand that you know all?

With respect.
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Old 2nd Jan 2018, 20:48   #317 (permalink)
 
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The authors, yes, but that leaves the rest of everybody not sure
What better way to make them read the posts rather than skim and not understand.The boost unit, faulty or not, had no role to play as to accident causation, because the sole cause was a separated control cable, even though the CAB says "probable" cause.
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your irreverent demand that you know all
Not the case at all, but boy, there is a load of nonsense on this thread by those taking a hammer to the CAB.
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Old 2nd Jan 2018, 21:36   #318 (permalink)
 
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What better way to make them read the posts rather than skim and not understand.The boost unit, faulty or not, had no role to play as to accident causation, because the sole cause was a separated control cable, even though the CAB says "probable" cause.Not the case at all, but boy, there is a load of nonsense on this thread by those taking a hammer to the CAB.
I applaud your effort at promoting engagement. I have a favor to ask. Am having difficulty downloading the final. Do you have a link?

But this: “...boost unit faulty or not, had no role to play....” say again?

Only this possibility springs to mind: If seized, the unit prevents all control of the ailerons, since “manual control” operates through the hydraulic arm. If jammed, there are no ailerons... with or without pumps on. With or without handles engaged....

Most appreciative.
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Old 2nd Jan 2018, 22:44   #319 (permalink)
 
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If seized, the unit prevents all control of the ailerons
Design requirements are that in event of ANY sort of boost failure the system can be disengaged. The applicable rule says,
Quote:
Each hydraulic system must have means located at a flight crew station to indicate appropriate system parameters, if It performs a function necessary for continued safe flight and landing; or In the event of hydraulic system malfunction, corrective action by the crew to ensure continued safe flight and landing is necessary
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say again?
OK, the boost unit, faulty or not, had no role to play as to accident causation, because the sole cause was a separated control cable, even though the CAB says "probable" cause.
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Old 2nd Jan 2018, 23:13   #320 (permalink)
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Originally Posted by Concours77 View Post
If seized, the unit prevents all control of the ailerons, since “manual control” operates through the hydraulic arm.
The disengage handle when pulled disconnects the control cable from the boost unit for aileron, rudder or elevator, and simultaneously alters the mechanical advantage. The full range of the control surface is reduced by about half, and the force required by the pilot is about doubled.

Pulling the engage handle reverses the action.

I discuss this in the new chapter currently at https://we.tl/x0L59Bpfmj and it will be in the next release.
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