AA77 FDR Data, Explained
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jaydeehess
Penultimate Amazing
For those of you so inclined, perhaps you could get a ballpark number for acelleration due to hitting the genset.
You would be doing a lot of estimating though.
The genset had a velocity imparted to it by the impact in momemtum transfer.
We can also estimate how long it took for the genset to come to a halt and how far it travelled. That gives us an average velocity of the genset.
Now plug that into a conservation of momentum formula for the system consisting of the aircraft and the genset with values for the mass of both the aircraft and the genset and the initial velocities of both of them , and the final(average velocity of the genset after collssion.
Solve for the final velocity of the aircraft, now you have a number for delta V. delta T will be the time of contact between aircraft and genset and you have a ballpark for the decelleration.
I just am unsure how big this ballpark will be given the uncertainties. +/- 5 times? , a order of magnitude?
The other way of doing this would be to assume a negative 1 g for the a/c and work bacxkwards to come up with a velocity for the genset and deceid if its way too high or way too low to have caused it to move as far as it did.
You would be doing a lot of estimating though.
The genset had a velocity imparted to it by the impact in momemtum transfer.
We can also estimate how long it took for the genset to come to a halt and how far it travelled. That gives us an average velocity of the genset.
Now plug that into a conservation of momentum formula for the system consisting of the aircraft and the genset with values for the mass of both the aircraft and the genset and the initial velocities of both of them , and the final(average velocity of the genset after collssion.
Solve for the final velocity of the aircraft, now you have a number for delta V. delta T will be the time of contact between aircraft and genset and you have a ballpark for the decelleration.
I just am unsure how big this ballpark will be given the uncertainties. +/- 5 times? , a order of magnitude?
The other way of doing this would be to assume a negative 1 g for the a/c and work bacxkwards to come up with a velocity for the genset and deceid if its way too high or way too low to have caused it to move as far as it did.
There is a parameter YAW FORCE LINK POSN in the data frame layout 757-3b_1.txt. Would that be a measurement of the yaw of the aircraft?
Warren.
ETA: The YAW FORCE LINK POSN parameter is measured in degrees.
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I once did exactly this some years ago -- and yes, I did a lot of estimating. This kind of rough calculation is not definitive, but it is enough to rule whether an idea is plausible or implausible.
Using these ballpark figures, if the estimated impulse resulted in a force on the aircraft enough to decelerate it by 1 g, i.e approximately 1 MN, it would have persisted for about 0.1 seconds. This is reasonably close to the time resolution of the instrument at 0.25 seconds.
So, to my surprise, I conclude that it is possible that the blow recorded here was caused by the large industrial generator (along with whatever else the aircraft was plowing through at that instant). This kind of collision, with the engine, would also have definitely disrupted power on the aircraft, and might explain why the record now appears to end exactly here.
Yes, if we can correlate the left lateral deaccel with a yaw direction that might tell us a lot more.
Is there any description of that parameter, Warren? I didn't see it listed in the AA77 FDR report, which shows where the parameters originate. It'd be easy to figure out what it's measuring if we knew what module or sensor it's looking at. Otherwise, all we can do is guess. I'm guessing it's probably related to rudder ratio or possibly even the rudder position sensor that's in the rudder actuator linkage(in which case, there should be three).
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tfk said:
My first instinct was a preliminary impact, but I could conceivably see it being the main impact as well. But I'm no more qualified to accurately opine than any one of the lurkers in this thread. I'll defer to RMackey, beachnut, Reheat and the other aeronautical geeks!
I had a look at one earlier(it was a slow day) and it's just 4 5/16th bolts and an electrical connector. The case looked pretty solid, but it's mounted to the airframe no better than anything else. It's not mounted on the keel beam either as I suspected, but the left inboard wheel well wall(technically not a bulkhead)
I'd agree with Mackey that the engine impact could have wiped out power to the accelerometer which wouldn't necessarily have full scaled the measurements right away(hysteresis?)
Almost impossible to determine, right?
I suspect that the reason that the parameter is not listed in the AAL77 FDR Report is that it is not listed in the other data frame layout D226A101-3G.pdf. I have no other information on it. I'll try decoding it as per the data frame layout 757-3b_1.txt anyway and see whether it produces sensible values or nonsense.
Warren.
ETA: I've just realised that if I decode it as I suggested, All I can get is 0's since the formula given for converting raw values to degrees is Degrees = 0 * Raw Value + 0. Therefore I won't bother any more with this parameter.
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Ap,
The strength of the mounting won't be determined only by the size & number of the mounting hardware, of course. But by the ratio of the strength of the hardware to the mass of the box. (And the strength of the item to which it is bolted, of course.)
Anything that glitched the power bus (or generated EMF spikes) could have put lots of gibberish into the data.
Impossible for us.
But, for a committee of engineers who are experts in each of the related components, you'd be amazed at what they can figure out when their assessments are based on knowledge, instead of wild-ass guesswork heavily seasoned with paranoia.
My inclination, from reading all of this, is "don't even bother trying to explain it". We've got too may unknowns, not enough real expertise here to distinguish THE explanation from a large number of COMPLETELY PLAUSIBLE explanations.
Plus the significance of this one "1/8th second of questionable data" is, in the grand scheme of things, indistinguishable from zero.
And I'd apply the same conclusion to all data frames back to where I was certain that the data was solid & uncompromised.
And this may be exactly what the NTSB did. Although 4 seconds worth of data seems like a lot to me.
But, then again, I'm not an expert.
Tom
The strength of the mounting won't be determined only by the size & number of the mounting hardware, of course. But by the ratio of the strength of the hardware to the mass of the box. (And the strength of the item to which it is bolted, of course.)
Anything that glitched the power bus (or generated EMF spikes) could have put lots of gibberish into the data.
Impossible for us.
But, for a committee of engineers who are experts in each of the related components, you'd be amazed at what they can figure out when their assessments are based on knowledge, instead of wild-ass guesswork heavily seasoned with paranoia.
My inclination, from reading all of this, is "don't even bother trying to explain it". We've got too may unknowns, not enough real expertise here to distinguish THE explanation from a large number of COMPLETELY PLAUSIBLE explanations.
Plus the significance of this one "1/8th second of questionable data" is, in the grand scheme of things, indistinguishable from zero.
And I'd apply the same conclusion to all data frames back to where I was certain that the data was solid & uncompromised.
And this may be exactly what the NTSB did. Although 4 seconds worth of data seems like a lot to me.
But, then again, I'm not an expert.
Tom
Where did Bob say this, on his site or somewhere else? I always thought he was one of those "We give no theories" type truthers?
Balsamo says he offers no theories but he is too stupid to understand he does offer 11.2g theories each time he makes up a new delusion. Balsamo said 77 was too high to hit the Pentagon, and proved wrong as all of 77 passengers and parts are there at the Pentagon. Not deterred by facts and evidence in his zeal to sell his pathetic lies, Balsamo claims to have all these experts on board and he makes up delusions about flying and the FDR in hopes he can sell the dumb down tripe to other paranoid conspiracy theorist like himself, math-less and unable to comprehend reality.
The 4 missing seconds of data were given to him by the NTSB and he and his non-experts (biggest expert is a saleman spewing .5 seconds can't be missing, oops 4 seconds were missing and the saleman was unable to help; he could only spew the fact the internal delay to store the value in the secure FDR chip had to be less than .5 second, and has nothing to do with missing data) were unable to decode the data because Balsamo is not after the truth he is selling delusions to paranoid dumbed down math-less conspiracy theorists, knowledge free and unable to form rational conclusions.
Here is the p4t standard post on a value of -1g as 77's engine may be hitting something. The -1g is the maxium value allowed to be stored.
Notice the p4t kool-aid dispenser say 77 was vaporized; it was not. There were thousands of pieces of 77 which were identifiable as 757 fuselage parts. So the standard dirt dumb conspiracy theorist rhetoric is in full swing at terrorist-apology land, Balsamo's dirt dumb kool-aid bar where you can't be banned for being stupid, you are made administrator. Reward for being stupid from the 11.2g failed physics master, Balsamo.
The -1g is the largest value stored (aka, the minimum value which you would feel as flying forward out of your seat as you are stopping, or hitting an object)
The interesting part of these parameter listing is they give resolution to time with values collected at specific locations in time like value sampled at 4hz, this give us a time stamp for various values stored in the FDR for each second.
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Mr.Herbert
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some one is posting under the name R_Mackey @ AboveTopSecret.com. (on this topic)
http://www.abovetopsecret.com/forum/thread512723/pg7
http://www.abovetopsecret.com/forum/thread512723/pg7
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WildCat
NWO Master Conspirator
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I wonder if Cap'n Bob is impersonating him?some one is posting under the name R_Mackey @ AboveTopSecret.com. (on this topic)
http://www.abovetopsecret.com/forum/thread512723/pg7
W.D.Clinger
Philosopher
I'm going to defend the salesman (presumably Ed Sanata of L3 Communications). Rob Balsamo asked Sanata about the "typical time lag" under normal conditions. Sanata responded with "Per ED55, it shall not exceed 0.5 seconds." That is indeed the average time lag implied by the 1 Hz sampling rate under normal conditions.
Ever since then, Balsamo has been trumpeting 0.5 seconds as the worst-case latency between measurement and recording, even under the abnormal conditions of a horrific crash. That is mathematically impossible.
It is also a gross misinterpretation of what Ed Sanata actually said, in response to a question that Balsamo had misworded so badly as to render its answer irrelevant.
Here is the conversation I had with Rob Balsamo concerning this point:
http://www.ccs.neu.edu/home/will/Music/Jokes/Balsamo/final5.txt
http://www.ccs.neu.edu/home/will/Music/Jokes/Balsamo/final6.txt
http://www.ccs.neu.edu/home/will/Music/Jokes/Balsamo/final7.txt
http://www.ccs.neu.edu/home/will/Music/Jokes/Balsamo/final8.txt
For more on Balsamo's mathematical incompetence, specifically his calculations of 11.2g and 10.14g, see
http://www.ccs.neu.edu/home/will/Music/Jokes/Balsamo/balsamo2.html
Finally, I strongly suspect that the R_Mackey who's been posting over at AboveTopSecret is indeed one of Rob Balsamo's sock puppets. Who else would say "Pressure IS altitude." ?
Will
Mr.Herbert
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I have to assume so. Captain Douche-Bag is still hurting from the they way his own member shot a million MORE holes into his CT dreams.
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Mr.Herbert
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Will... GREAT stuff! A must read for everyone
Captain Bob said:
W.D. Clinger said:
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jaydeehess
Penultimate Amazing
As for the accuracy of pressure alt vs. radar alt.
I believe it may have been pointed out that the ground proximity warning system now uses both a terrain map in the computer, plus GPS postional data, plus the radar alt to warn pilots that on their present course they will hit terrain. The newer systems can give a pilot a full minute's warning. They simply cannot rely of pressure alt for this, it would be folly to do so.
I believe it may have been pointed out that the ground proximity warning system now uses both a terrain map in the computer, plus GPS postional data, plus the radar alt to warn pilots that on their present course they will hit terrain. The newer systems can give a pilot a full minute's warning. They simply cannot rely of pressure alt for this, it would be folly to do so.
jhunter1163
beer-swilling semiliterate
The real R. Mackey wouldn't say something as stupid as "Pressure IS altitude."
ETA: Last post in page 7, the faux R.Mackey says just that. He says other stupid things too, but that was the one that jumped out at me.
ETA: Last post in page 7, the faux R.Mackey says just that. He says other stupid things too, but that was the one that jumped out at me.
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No matter what the new decoded data shows they will find some way to argue about it. This is the very essence of twoofer irreducible delusion.
They already are doing this very thing by arguing the accuracy of the pressure altimeter. For example both Turdoofan (the self described technologist) and the chief loon of the "verified by the FAA" cult by providing links to the FAA mandated specs for altimeter accuracy and insisting it's 20'. Well, it is for the instrument itself, but it's operational accuracy as an installed SYSTEM is 75'. It's just another example of their misleading scumbag attempts to deceive. Other twoofers buy it, so it works for their purposes. The entire gambit is to use thing that appears reasonable to the knowledgeable. The continued reference to the use of the pressure altimeter for precision approaches is also misleading in that TERPS (the rules under which approaches are designed) takes into consideration the allowable tolerances to include a possible 75' altimeter error.
Unfortunately, for their arguments, AA 77 was well above tested parameters for which any errors are unknown. In essence, this continued argument that the pressure altimeter trumps the radar altimeter under the conditions encountered by AA 77 is well beyond a silly stupid argument. It is absurd!