AA77 FDR Data, Explained

[wstutt]

Hi apathoid,

I wouldn't call these errors large. There are just many variables and the 757's static system wasn't certified to be accurate in that type of flight regime. The lag and source error beachnut keeps talking about is very real. I see it when I test and certify these systems, particularly the lag as I've rarely encountered source errors of 50' or greater.

In what flight conditions is the 757's static system certified to be accurate?

Do you think the 120+ foot error at the end of the flight that Rob is claiming is more due to lag than source error?

I appreciate your dispassionate approach to this problem Warren, and if you ever need any other technical assistance...take what you get from Rob with a boulder size grain of salt, and look here first.

Thanks again for all the hard work!

Your welcome.

I've been discussing the pressure altitude on the Pilots for 9/11 Truth forum here

Warren.

 

[beachnut]

Hi apathoid,

In what flight conditions is the 757's static system certified to be accurate?

Do you think the 120+ foot error at the end of the flight that Rob is claiming is more due to lag than source error?

Your welcome.

I've been discussing the pressure altitude on the Pilots for 9/11 Truth forum here

Warren.

Balsamo agrees to 120 feet of lag? Case closed. Cool

Flight 77 altimeter is only 90 feet off when it reads -99 feet.

 

[wstutt]

Hi beachnut,

Balsamo agrees to 120 feet of lag? Case closed. Cool

No he doesn't agree. He says that the pressure altitude is 120+ feet too high.

Flight 77 altimeter is only 90 feet off when it reads -99 feet.

How did you calculate only 90 feet?

Warren.

ETA: What I was meaning to ask was given that apathoid had said that he rarely encountered source errors of greater than 50 feet, would the apparent 120 foot error at the end of the flight be more due to lag?

 

[beachnut]

Hi beachnut,

No he doesn't agree. He says that the pressure altitude is 120+ feet too high.

How did you calculate only 90 feet?

Warren.

ETA: What I was meaning to ask was given that apathoid had said that he rarely encountered source errors of greater than 50 feet, would the apparent 120 foot error at the end of the flight be more due to lag?

The 120 looks good for the deed. I found 50 feet was a valid number for FDR PA to be off on normal operations during takeoff at normal speeds and maneuvers. With 120 we have to come up with 70 feet of errors, lag is a good source at 3500 fpm decent and speed is a great error of pressure problems. I have seen studies and in those studies using Boeing aircraft the typical altitude error rose with speed. Lag is an error even Balsamo can't wave off with paranoid anti-government neoNAZI dumbness.

The last reading of PA could be over the overpass about 800 feet out from impact. The plane would be 80 feet MSL about 20 feet above the local ground, very close to a RADALT reading of 4 feet which is about 16 feet above a car top, tree, dirt, truck, or something. Rough stuff based on the value position in time in the FDR. 120 looks better than my smaller number.

Since 77 did impact the Pentagon, we have the FDR showing the real values, and we have a good model for errors at 483 KIAS (233 knots over normal, highest legal speed in the USA at 50 feet AGL), pulling 1.7 gs average, and in a decent 5 times higher than a normal landing approach. Think we can have some errors in a +-75 foot static check device?

Balsamo is selling dirt dumb paranoid conspiracy theories for idiots; he can't let reality in to mess up his DVD sales and loose the dolts who spew praise on his delusional offer no theory failed physics.

I hear the bus coming, I would step back from the edge my friend.

I was thinking it was close to 90, but 120 looks good for crossing the highway, near the overpass. have a great holiday

 

[beachnut]

Hi beachnut,

No he doesn't agree. He says that the pressure altitude is 120+ feet too high. ...

Balsamo is an idiot. First he has said the 757 can't go 483 KIAS and his expert dolts, other pilots who joined the club of dummies, agree and say far out failed ideas to support their paranoid delusions.

But now!

(balsamo says)The 757 is rated for .86M, .70-.72M as displayed in the data is well below the certified limits of the pitot-static system

NOW, the 757 speed of 483 is a normal speed so the altimeter has to be within what, the +-75 feet when we check it on the ground not moving, not flying, not much of anything going on.???

Balsamo is selling lies, your reality work is not in his interest. The top speed for 757 at sea level is 350 KCAS or so, not 483 KIAS, so the 757 is not in a normal zone. There is a big difference in 483 KIAS at sea level and .86 MACH at 35,000 feet, but then Balsamo is a 2,223 G expert, so his idea of reality is off by many magnitude when it comes to selling lies, implied lies based on his offer no theory delusions.

The errors at higher altitudes where 757 can fly at .86 MACH are much higher for the altimeter. So if Balsamo wants .86 MACH to be normal thing at 50 feet MSL, then he has to have the higher altimeter errors that go with that speed and 200 feet is not out of the question. But who expects an engineer who worked at AFWAL and is an ATP rate pilot with thousands of hours in heavy jets who has flown .9 MACH in a 707 airframe for hours to have a clue. I would not trust me either, but I know 77 hit the Pentagon and it is a fact proved many times over. Even a grade school kid has the education to form the reality conclusion on 77; No wonder Balsamo never earned an ATP.

Now 483 KIAS is normal. cool; what happen to too fast for Vmo of 350? Now .73 MACH at 50 feet is p4t approved! Airspeed at Pentagon now p4t approved; news at 2,223 Gs. lol

Balsamo has no clue, he looks up stuff and comes up with 2,223 Gs when it is clear 77 was averaging 1.7 G the last two seconds and then impacted the Pentagon. Funny stuff.

 

[apathoid]

ETA: What I was meaning to ask was given that apathoid had said that he rarely encountered source errors of greater than 50 feet, would the apparent 120 foot error at the end of the flight be more due to lag?

Well there is a caveat with that assertion. Under normal test conditions, using normal 757 test altitude and speed pressures: the most I've seen is 50 feet or so. The test setup we use simulates a perfect atmosphere, not subject to turbulent airflow, compressibility and any other factors that may throw off an accurate measurement.

As beachnut pointed out, the altimetry accuracy is a function of airspeed as well, and a higher airspeed means a high delta "P" between pitot and static systems, especially at low altitudes. This delta "P" or what our manual refers to as "impact pressure" is what we base the accuracy measurements on. At low speed/low altitudes, impact pressure is low so the accuracy is quite fine +/- 40' or so. As the delta "P" increases with airspeed, our last test point of 400 kts, the accuracy is +/- 125'.

That said, I do feel we are looking mostly at lag; its something I've seen during pitot-static tests and its effects are known. Instrument lag is a big reason Vertical Speed Indicators(VSI) now use accelerometers to eliminate the lag, they are called IVSI's.

"An instantaneous vertical speed indicator (IVSI) displays vertical speed information with essentially zero, time lag. A single pointer indicates rate of altitude change against a fixed circular scale much the same as a vertical speed indicator (see Instantaneous Vertical Speed Indicator figure on the right).This instrument is similar in operation to a vertical speed indicator, except that accelerometers have been added to the linkage between the capsule and the pointers. These sense accelerations of vertical velocity and provide appropriate motion to the pointer before any static pressure differential has been established."

 

[apathoid]

Balsamo is an idiot. First he has said the 757 can't go 483 KIAS and his expert dolts, other pilots who joined the club of dummies, agree and say far out failed ideas to support their paranoid delusions.

But now!
NOW, the 757 speed of 483 is a normal speed so the altimeter has to be within what, the +-75 feet when we check it on the ground not moving, not flying, not much of anything going on.???

Classic Balsamo "heads I win; tails you lose" form of argument. He changes his arguments to support whatever newest pet theory he has. And when you tell that many lies, it gets kinda hard to keep up with all of them. Cognitive Dissonance apparently has zero effect on first officer Robbie, or truthers in general.

Also, notice how when he gets backed into a corner, he always has a cop-out ready ie "we dont any evidence that the FDR is actually from N644AA, therefore this data means nothing".

Balsamo has no clue, he looks up stuff and comes up with 2,223 Gs when it is clear 77 was averaging 1.7 G the last two seconds and then impacted the Pentagon. Funny stuff.

 

[9/11 Chewy Defense]

If I had a diaper factory for all the **** the Truthers put out, I'd be a multi-millionaire!

 

[wstutt]

<snip>

As beachnut pointed out, the altimetry accuracy is a function of airspeed as well, and a higher airspeed means a high delta "P" between pitot and static systems, especially at low altitudes. This delta "P" or what our manual refers to as "impact pressure" is what we base the accuracy measurements on. At low speed/low altitudes, impact pressure is low so the accuracy is quite fine +/- 40' or so. As the delta "P" increases with airspeed, our last test point of 400 kts, the accuracy is +/- 125'.

<snip>

Thanks apathoid,

Is that test point of 400 kts with accuracy +/- 125 feet you referred to at low altitude on a 757?

Would the parameter named TOTAL PRESSURE in the FDR file be related to impact pressure?

After following the discussion over here, I pointed out the possibility to Rob of the high total pressure causing a greater error in the pressure altitude reading:

I see that the total pressure (which I realise is not static pressure because it also depends on airspeed) increases to 1400mB in the NTSB CSV file towards the end of the flight. Using my decoder, I see that the total pressure never rises above 1058mB in any of the other flights in the FDR file.

Was the pressure altitude reading on the aircraft calibrated to correctly remove errors at such high total pressures? I don't know.

Here's what Rob said in reply:

Every type of aircraft goes through a rigorous type certification process. The "Flight envelope" of the 757 is .86M and is tested above those speeds. The Static system is tested to such speeds and calibrated to remove such errors.

Warren.

 

[apathoid]

Thanks apathoid,

Is that test point of 400 kts with accuracy +/- 125 feet you referred to at low altitude on a 757?

No, we test high speed accuracy with a high test altitude and vice versa. We don't do a test for low altitude accuracy at high speed. In fact, the manual gives explicit instructions not to do this as the resulting high delta "P" can damage the bellows in the Air Data Computer, Standby Altimeter and Elevator Feel Computers.

So I cant give you a +/- for the exact profile flight 77 was flying; we simply don't test anything remotely resembling that.

Would the parameter named TOTAL PRESSURE in the FDR file be related to impact pressure?

First of all, I misspoke in my last post. "Impact pressure" is another way of saying pitot pressure. As airspeed(impact pressure) increases, the difference in pressure between pitot and static pressures increase, especially at low altitude, increasing the error. I'll try to find something in the ADC's repair manual that illustrates this and I don't think I did a real good job explaining it. It's one of those things that kinda needs to be seen in person.

After following the discussion over here, I pointed out the possibility to Rob of the high total pressure causing a greater error in the pressure altitude reading:
Here's what Rob said in reply:

Every type of aircraft goes through a rigorous type certification process. The "Flight envelope" of the 757 is .86M and is tested above those speeds. The Static system is tested to such speeds and calibrated to remove such errors.

That was a total non-answer because he has no clue about how these systems are designed, calibrated and subsequently tested. Yes, the 757 is capable of Mach 0.86, but only at very high altitudes. He apparently has no concept of a flight envelope. An aircrafts V_mo changes with altitude. If he has any documentation that the 757 is certified to fly 80 kts above V_mo, tell him produce it or retract his claim.

eta: Just to highlight the dizzying incompetence of this statement by Rob: "The "Flight envelope" of the 757 is .86M and is tested above those speeds". He's trying to say the 757 is certified to fly Mach 0.86 regardless of altitude. That's like saying the SR-71's flight envelope is Mach 3.5, so it must be able to fly that at sea level, right?

Try 0.7 Mach http://hsc.csu.edu.au/engineering_studies/aero_eng/3057/images/figure2.gif

 

[Pinch]

eta: Just to highlight the dizzying incompetence of this statement by Rob: "The "Flight envelope" of the 757 is .86M and is tested above those speeds".

The aerodynamic accuracy of that statement is so stupefyingly disingenuous, one can't begin to address it.

Cap't Bob Balsamo is speaking as if the "flight envelope" is a singular entity; a flat, one dimensional element made of of a single maximum speed.

A more accurate statement would have been: "The "Flight Envelope" of the 757 includes an upper airspeed limit of .86M at flight level XXX. Certain aeronautical testing does occur above those speeds, but only in a tightly controlled test environment by qualified test pilots and using test-program developed deviations outside of the airspeed/altitude "flight envelope" to garner specific data points".

If Balsamo has evidence of the low-altitude/high speed test regime the 757 was subjected to that includes errors produced by the pressure altitude system because of the aforementioned flight-test environment, he should be more specific in his statements. As it is, PfT and CIT and the other treeforts routinely post shoddy, poorly researched and junior-high school-quality information that impress their so-very-easily-impressed sycophants but are seen as pur ecrap by those who know what this is all about.

Specificity is the very soul of credibility, and Balsamo displays none of this in any way, shape or form. It IS funny, though, watching him hold forth on his site, yelling like a aeronautical Lear against a storm of logic and science. I hope he doesn't stop. Makes the monthly Comcast ISP bill that much easier to pay.

 

[alexi_drago]

............
I hope he doesn't stop. Makes the monthly Comcast ISP bill that much easier to pay.

You seem to be in luck, he's not giving up on this cockpit door.

If you cannot provide such a document stating a different state for 0 other than CLOSED, the only conclusion is that the data provided by the NTSB is in DIRECT conflict with the govt story once again. A Flight Deck Door CLOSED condition makes a hijack impossible. This is straight forward and undisputed.

bolding mine.

 

[BCR]

This is straight forward and undisputed

Another lie...

 

[Pinch]

You seem to be in luck, he's not giving up on this cockpit door.

If you cannot provide such a document stating a different state for 0 other than CLOSED, the only conclusion is that the data provided by the NTSB is in DIRECT conflict with the govt story once again. A Flight Deck Door CLOSED condition makes a hijack impossible. This is straight forward and undisputed.

And what makes this turd *really* shine is that, without taking a breath, he states that the data he bases his above statement on is invalid because

"...even if we obtain the Maintenance Manual from American, we must first determine the data is from an American Airlines aircraft, N644AA. This is why i have repeatedly stated this data is not "proof" of anything.

Proof positive that a box of hammers is smarter than Cap't Bob Balsamo.

 

[beachnut]

... Proof positive that a box of hammers is smarter than Cap't Bob Balsamo.

Or any box of rocks.

Balsamo has a big problem with physics and flying information.

On lag he says 77 is level at the end of data, and tries to minimize lag after giving up .5 to 2 seconds of lag are typical. I feel sorry for the "kool-aid cult dolts" when they figure what 2 seconds of lag mean even if you do level off at 1.7 G.

What are the errors in PA when you check the darn thing at +-75 feet under static conditions. Balsamo, this means zero airspeed, sitting still, at a known location. Wake up p4t dolts, your fearless leader is selling DVDs for 10 bucks, dumbed downed for those who love "offer no theory", about 2,223 Gs of no theories.

2,223Gs? I thought 11.2 Gs was dumb but never thought someone could move that many orders of magnitude more stupid.

The data in the FDR show the exact errors in the PA. Warren has the final numbers which confirm 77's impact; watch out for the bus of dolts coming to run him down.


Level?
Level flight was 1.1 pitch, so Balsamo's level flight claim for 77 may not be a fact he can back up with the flawed fish-eye distorted lens of the Pentagon's super high speed (compared to balsamo) camera.
The final pitch looks like it was down. Oops... -2.3 -2.1 -1.8 -1.2 The last 4 pitch angles from the FDR FOUND IN THE PENTAGON, you know Flight 77's FDR.

The G force found in the FDR can be used to estimate the final VVI of ~348 feet, negative. That is down for p4t core members. (as in not level)

How dumb do you have to be to be a p4t core member?

 

[apathoid]

With Tino(turbofan), Warren, and JFK....PfT's tech guys....all calling him out on his cockpit door idiocy, it's a wonder Cap'n Booby is still clinging to this one. There is absolutely no one left backing him on this anymore; all of the forum groupies(all five of them) seem to agree with the above three.

But saving face is apparently not an option to this outright fraudster. Since he's spammed this "finding" far and wide, he knows he can't quietly retract this claim without major damage to his truther "street cred". He also knows only a tiny fraction of the black tee-shirt brigade will actually research this claim and subsequently find that it's bogus. There is no such thing as a bad batch of snakeoil to Booby - for every one of his closest allies who call him out of this crap, he knows there are a hundred more who gladly swallowed every drop of it.

Basically, he'd rather continue looking like an assclown than admit that the GL's...along with his "tech guys"..were right all along.

 

[apathoid]

And what makes this turd *really* shine is that, without taking a breath, he states that the data he bases his above statement on is invalid because

"...even if we obtain the Maintenance Manual from American, we must first determine the data is from an American Airlines aircraft, N644AA. This is why i have repeatedly stated this data is not "proof" of anything.

Proof positive that a box of hammers is smarter than Cap't Bob Balsamo.

Yup. I also highlighted this glaring contradiction at the ATS forum. I guess if you are really really stupid, as Balsamo is, stating the above may seem like a good idea because you are right either way. Data is fake = inside jorb. Data is real/contradicts the official story = inside jobby job.

However, most rational people with IQ's over room temperature see this for what it is - a mental midget, who's in way over his head, making excuses for his thoroughly destroyed claim.

 

[apathoid]

Happy 2010 everyone!

I'm cross-posting this from the ATS forum. It's relevant to the recent discussion here...



I'll revisit the altimeter lag argument shortly, if anything just to tie up the loose ends from this discussion. I believe lag played a large part in the error of the pressure altitude in the final moments, but showing "proof positive" that lag caused the error is unnecessary. Here's why...

A short dialog with Warren Stutt, in reference to PfT's pressure altitude argument, got me thinking along some different lines. I suppose I knew all along that the 757's Air Data Computing/Pitot-Static System wasn't designed for such a flight profile as AA77s final "attack run", but I didn't think I could demonstrate such without information not currently at my disposal. A question from Warren about a parameter - Total Pressure(which I'll refer to as Pt)- got me digging in the manual about pressure limits. Long story short, I found a few things that should bury the "pressure altitude reads too high" issue for any rational mind.

I'll show the following:

- AA77 was travelling at 488 knots True Air Speed(TAS) at the end of data, some 141 knots above the 757's max operating speed(VMO). This obviously means that AA77 was operating well beyond the 757 flight envelope; meaning that the Air Data system was never tested, calibrated, or certified for such extreme conditions.

- The Total Pressure(Pt) at the end of data exceeded 42 in/Hg, resulting in a differential pressure of over 12 in/Hg between Total Pressure(Pt) and Static Pressure(Ps) This is important because, as I'll show, the 757 Maintenance Manual states that differential pressures over 10 in/Hg can cause damage to the Pitot-Static System. Enough said.

- The Air Data Computer is never tested for anything approaching the pressures that AA77 experienced approaching impact. As I'll show, pitot and static(speed and altitude) pressures are tested in pairs(this is because the Air Data Computer is calibrated to condition raw static/altitude data with different airspeeds, angle of attack, and air temperatures) which check only low speed/low altitude and progress in a linear fashion to high speed/ high altitude. High speed/low altitude profiles are not tested, and we can assume that the ADC is not calibrated to be accurate in such a regime, especially given how far beyond the flight envelope AA77 was.

- Finally, and probably most importantly: The 'Air Data Accuracy Test' allowable errors pertain to test conditions only, and don't include error from "..the aerodynamic effects of flight". Rob Balsamo will try to have you believe that the error pertains to flight conditions. I'll show that it doesn't.


757 Flight Envelope/VMO


Reference: 757 Air Data Accuracy Test

The far right hand column is the computed VMO(or Velocity, Maximum Operating) based on input pressures which simulate a range of airspeeds and altitudes. You'll notice that from 0' up to 18,000', the 757's VMO is 347 knots. The speed at the end if data is 488 knots, some 141 knots over VMO. That's not barely past the envelope; its into uncharted territory. No 757 has flown that far beyond VMO and lived to tell the story.

Why is any of that trivial information important? Because Air Data Computing Systems are only designed, tested, and calibrated for conditions within the airplanes performance envelope and perhaps even slightly beyond.



Differential Pressure Beyond Damage Threshold.


Reference:
757 Air Data Accuracy Test(from Boeing's Maintenance Manual.)
FDR Decode - Airspeed and Total Pressure(Pt) Fields at End Of Data
Total Pressure Conversion

Note the large bolded text at the beginning of the procedure which states:

"MAKE SURE THE DIFFERENCE BETWEEN TOTAL PRESSURE AND STATIC PRESSURE DOES NOT EXCEED 10 IN/HG....THIS WILL PREVENT DAMAGE TO THE PITOT-STATIC SYSTEM"

What that means is you cannot supply too high of an airspeed for a given altitude, or damage can occur. I've actually damaged and Air Data Computer once by not heeding a similar warning. The system is designed for only a certain range of pressures and up to a delta of 10 in/Hg between altitude and airspeed. This was grossly exceeded in the final moments of AA77's existence, as you will see.

Note the FDR Decode link above shows that Total Pressure(Pt) as 1442 mB's at the end of data. The Static Pressure(Ps) parameter is unavailable; however its not needed as we know that a pressure altitude of -99' MSL, AA77's altitude at end of data, is equivalent to 30.030 in/Hg. Since we have a mix of units, and we are looking for both units to be in in/Hg - we have to convert the 1442mB. Note the Total Pressure Conversion above and we'll see that 1442 mB is equal to 42.58 in/Hg. So we have:

a Total Pressure of: 42.58 in/Hg
a Static Pressure of: 30.03 in/Hg

..giving us a difference in pressure of 12.55 in/Hg. What did that note say again?

"MAKE SURE THE DIFFERENCE BETWEEN TOTAL PRESSURE AND STATIC PRESSURE DOES NOT EXCEED 10 IN/HG....THIS WILL PREVENT DAMAGE TO THE PITOT-STATIC SYSTEM"

There ya go, moving on...



Air Data Computer Test Range


Reference:
757 Air Data Accuracy Test

Note the Maintenance Manual figure above. With a given set of test pressures(at left), you'll see the output altitudes and speeds with an accuracy figure and "delta" figure. The thing that's important here is the range that is being checked, note that the only airspeed checked with 0' altitude is 150 kts. The full range goes like this:

0' 150 kts
10,000' 200 kts
20,000' 300 kts
30,000' Mach 0.75
35,000' Mach 0.80
40,000' Mach 0.85

This is the calibration range that is tested for accuracy. Note that there is no 0' 490 kts test point, or anything remotely close to it. As I mentioned, the Air Data Computer is calibrated over the normal flight envelope, and this test shows that there are no tests for any speed/altitude combination outside that flight envelope. Actually, it even shows that only a relatively small range within the flight envelope is checked for accuracy - that being only the typical airspeeds for the given altitude.

The other thing to notice, again, is the difference between Total and Static Pressures(these are at left). You can see that over the test range, the maximum difference is about 4.8 in/Hg. Recall what AA77 was experiencing in the final moments; 12.55 with 10.0 being the damage threshold.



Air Data Computer Accuracy


Reference:
757 Air Data Accuracy Test


I'll keep this point short. Just note the highlighted portion at the bottom..

"..the aerodynamics of flight do not contribute to the tolerance allowance"

So, at 0' and 150 kts, a tolerance under test conditions of +/- 25' and +/- 2.0 kts is allowed. That is, to re-iterate, under perfect test conditions - not subect to aerodynamic disturbances. Rob will have you believe that the tolerance is for flight conditions, it's not. This renders any argument to the effect of "the accuracy for an altimeter at 0' MSL is +/-25', so AA77 is still (x)' too high." ...completely void, especially given how far beyond the flight envelope AA77 was.





I hope some of you found this to be enlightening. Most aviation experts here already kinda know most of this, but I thought showing it would be a good idea since these claims keep persisting. If anyone has any specific problems or corrections to the above, I'll gladly discuss them.

The meta-argument of whether or not the altimeter was slightly lagging behind is sort of moot, but I'll dig up some stuff on the ADC's Pt and Ps transducers for you, Tino. I've looked quickly through the 'Functional Test'(bench test) for those sensors and there isn't a test for lag, just accuracy tests, leak rate tests, and latency tests for the output ARINC data words. IIRC, these were something like 250,000-1,000,000 nanoseconds. But that's obviously not related to the lag I was talking about.

 

[Klimax]

Thans. Very interesting.

 

[BCR]

I hope some of you found this to be enlightening. Most aviation experts here already kinda know most of this, but I thought showing it would be a good idea since these claims keep persisting.

And just like NoC, 'these claims' will 'keep persisting'. I appreciate the post. It gives specifics for the generalizations that most of us familiar with physics understood intutitively. The system measures air pressure, but as air flows at different speeds and densities around any measurement system, the properties of the medium being measured change, thus the calibration parameters don't apply.

I had to give up ATS because it started causing my Norton's anitvirus software headaches. But even though you have explained it in terms even a simple minded non-pilot like me can understand, P4T has built their career around the plane being 'too high'. They will never admit to flying beyond spec speeds at sea-level having any impact on air pressure measurement systems.