Flight 77 FDR research

I would like help clarifying these items:

(1) Does the FDR (Flight Data Recorder) record off of its own pressure altimeter or does it record off of the Captains Altimeter?

(2) Or does it take its information from the air data sensing unit which shares that data with the Captains, F/O's and standby altimeter?

(3) Does the FDR sense and record both of the Capts. and F/O's barometric pressure setting?

Thanks.

Originally posted by nick7261
What I did notice looking throug the flight path studies at the NTSB web site is that none of the studies show the altimeter graph jump going through 18000 ft., either up or down. Maybe it happens so quickly that the data isn't visible on the scale of the graph. I have no idea.

Thanks as always for your encouragement and for looking into that. There's also no jump in the FDR study. Nor in the CSV file - altitude stays steady. I'd have to double-check the scale there, but it eems any sudden 300 ft jump would show - maybe not a big bump, but noticable. There are separate alt. and adjustment numbers in there - tho I haven't sorted it all out, the altitude reading don't seem to "jump" anywhere but upon alt set to 29.92 in the animation.

Originally posted by johnlear
I would like help clarifying these items:

(1) Does the FDR (Flight Data Recorder) record off of its own pressure altimeter or does it record off of the Captains Altimeter?

(2) Or does it take its information from the air data sensing unit which shares that data with the Captains, F/O's and standby altimeter?

(3) Does the FDR sense and record both of the Capts. and F/O's barometric pressure setting?

Thanks.

I hate to show my hand, but it's been laying out on the table anyway so lemme just confess these Qs are over my head almost entirely.
If you have Excel, you should be able to open and read the CSV even better than me, especially with your advanced knowledge, and see what's recorded.
71.18.155.196...
That and the Speciaists' study are the two sources that show raw data, basically every parameter. The answers are probably in there somewhere. I'd be quite interested to see anything interesting you find, and my brain would be well relieved to have someone else figure it out first.

Stepping out now. No more questions for the time being, my press secretary will take over from here.

[edit on 4-3-2007 by Caustic Logic]

Originally posted by johnlear
I would like help clarifying these items:

(1) Does the FDR (Flight Data Recorder) record off of its own pressure altimeter or does it record off of the Captains Altimeter?

Own altimeter of sorts (see point below).

(2) Or does it take its information from the air data sensing unit which shares that data with the Captains, F/O's and standby altimeter?

It takes raw data from the ADC (Air Data Computer), and assumes a barometric pressure of 29.92. This is to eliminate the possibility of any failures in other equipment.

Consider the following: the FDR is terminating at 175ft. To the average guy in the street, this would add up the the altitude of the ground floor of the Pentagon; case closed. Because it is an uncorrected pressure altitude, when we correct for pressure, we suddenly find that the aircraft is actually 310 ft HIGHER than that reported by the FDR.

The ground is approximately 175 ft ASL, the Pentagon is approximately a further 75 ft tall. 175+75 = 250 ft.

The FDR stops at 175 ft. 175 + 310 = 485 ft (actual aircraft altitude),

The aircraft is thus: 485 - (175 ft + 75 ft) = 235 ft above the Pentagon roof. It can't hit it based on the FDR data.

You'll also note that while the altimeters are reset, the altitude recorded by the FDR does not change. The pressure on the day adds 310ft to the altimeter reading when passing through FL180 in the descent. From the CVR, ATC tapes and this reading, crash investigators have sufficient data to know what the pressure was during the accident flight, in addition to ATIS reports from surrounding airports etc..

(3) Does the FDR sense and record both of the Capts. and F/O's barometric pressure setting?

Both.

I note that the rad alt is showing as an "unconfirmed or failed item" meaning the data off these are totally useless. I was looking for at least one rad alt to be operative (there are two - Capt and F/O), but both are otherwise unavailable. I find it hard to believe that so much data isn't available on the FDR.

www.caa.co.uk...

Page 23 is rather interesting. It shows the FDR error for pressure changes, and the amount of error that is permitted for the reading.

[edit on 4-3-2007 by mirageofdeceit]

Originally posted by Caustic Logic
I'd be quite interested to see anything interesting you find, and my brain would be well relieved to have someone else figure it out first.

Thanks for the link to the Flight Data Recorder CL.

I wanted to mention couple of things here. One is that all Transport Category Aircraft have an MEL (minimum equipment list). If the airplane is to be dispatched with something inoperative it has to conform to the requirement of the MEL and signed off as: Released with autopilot inoperative per MEL 1001—1-234. (not the real numbers).

The reason I mention this is I don’t believe any transport category aircraft can be released with BOTH radar altimeters inoperative. The reason is that the radar altimeter triggers certain audio altitude warnings or callouts and certain information to the autopilot. I will check on this.

Another thing I noticed is that channel B is Acceleration and measures the G forces 8 times every second of flight. For the last 10 seconds of Flight 77 the maximum recorded G’s is 1.75 G’s.

Then I noted that:

The airplane took of and climbed westbound (Channel F) to FL350 (Channel E) being hand flown, that is, not on autopilot LEFT or RIGHT (Channels L & M).

At 0825 (Channel A) while in the climb at 13,000 feet (Channel E) the RIGHT autopilot was engaged (Channel M).

At 0847 (Channel A) the airplane was level at 350 (Channel E) RIGHT autopilot engaged (Channels M).

At 0854 (Channel A) a left turn started with a 15 degree bank (channel J).

At 0900 (Channel A) a descent was started (Channel E).

At 0907:51 (Channel A) The RIGHT autopilot was disengaged (Channel M) at an altitude of about FL240 (Channel E) on a heading of 084 degrees (Channel F).

At 0910 (Channel A) the LEFT autopilot was engaged (Channel L) at about FL230 (Channel E).

At 0910:26 (Channel A) the LEFT autopilot was disengaged (Channel L) at about FL225 (Channel E).

At 0910:58 (Channel A) the LEFT autopilot was reengaged (Channel L) at about FL240 (Channel E).

At 0924:16 (Channel A) descending through FL180 (Channel E) both the Captains and the First Officers altimeters were reset to local barometric pressure of 30:24 (Channel CG & CH).

The descent was continued with the LEFT autopilot engaged (Channel L) until 0920 (Channel A) when the LEFT autopilot was disengaged (Channel L) at 7000 feet (Channel E).

The autopilot remained disengaged until alleged impact at 0937:46 (Channel A).

The heading of the airplane did not vary more than 1 degree from its heading of 070 degrees (Channel F) for the last 13 seconds of the flight. The bank angle did not exceed 8 degrees (Channel J) for the last 20 seconds (Channel A 0937:26 to 0937:46) of the alleged flight.

What this all of this tells me is that whoever was flying this airplane was very experienced in flying the airplane and in using the autopilot. He knew how to make the airplane turn and descend using the autopilot. He knew exactly when to reset the altimeters and set them to barometric pressure of 30.24. He then disconnected the autpopilot and began hand flying at 7000 feet, and then flew a very precise profile into the Pentagon.

Hijackers? Not a chance. And who gave them the local barometric pressure of 30.24?

And if there was one pilot who set the First Officers altimeter?

And how could they be so focused to set the altimeters at exactly FL180?

And why would they reset the altimeters? They were going to crash.

Many questions. I’ll look into this deeper tomorrow.

Can people see my posts?

At 0907:51 (Channel A) The RIGHT autopilot was disengaged (Channel M) at an altitude of about FL240 (Channel E) on a heading of 084 degrees (Channel F).

At 0910 (Channel A) the LEFT autopilot was engaged (Channel L) at about FL230 (Channel E).

At 0910:26 (Channel A) the LEFT autopilot was disengaged (Channel L) at about FL225 (Channel E).

At 0910:58 (Channel A) the LEFT autopilot was reengaged (Channel L) at about FL240 (Channel E).

At 0924:16 (Channel A) descending through FL180 (Channel E) both the Captains and the First Officers altimeters were reset to local barometric pressure of 30:24 (Channel CG & CH).

The descent was continued with the LEFT autopilot engaged (Channel L) until 0920 (Channel A) when the LEFT autopilot was disengaged (Channel L) at 7000 feet (Channel E).

The autopilot remained disengaged until alleged impact at 0937:46 (Channel A).

This is very odd in its own right. I'll get the FDR data myself and take a look. Is the AP itself recorded (set altitude, vertical mode, etc)??

I would expect a hijacker to just hit the AP disconnect bar (it is a big white rectangular bar below the three AP engage buttons that says "DISCONNECT" on it for those who don't know) and leave it at that.

For people who never flew 757s before, they sure seemed familiar with it.

[edit on 5-3-2007 by mirageofdeceit]

time pressure alt (CLIMBING)

8:27:58 30.21 17938
------------------------------ FL018
8:28:00 29.91 18015
8:28:02 30.21 18093
8:28:04 29.91 18170
8:28:06 29.94 18247
8:28:08 29.91 18324
8:28:10 29.92 18402
8:28:12 29.91 18483

Caustic Logic - is that a typo in there or do they really reset the altimeter to 30.21 then back to 29.91 after already setting it to 29.91??

[edit on 5-3-2007 by mirageofdeceit]

Originally posted by Caustic Logic

the recorded alt does not change at all with trim.

That is correct. Pressure altitude is recorded from the Air Data Computer and not affected by the altimeter setting on either the Captains or the F/O's altimters.

time trim alt
8:27:58 30.21 17938
------------------------------ FL018
8:28:00 29.91 18015
8:28:02 30.21 18093
8:28:04 29.91 18170
8:28:06 29.94 18247
8:28:08 29.91 18324
8:28:10 29.92 18402
8:28:12 29.91 18483

What channel are you reading here for barometric pressure setting? CG, CH or?

Thanks.

Originally posted by mirageofdeceit

time pressure alt (CLIMBING)

8:27:58 30.21 17938
------------------------------ FL018
8:28:00 29.91 18015
8:28:02 30.21 18093
8:28:04 29.91 18170
8:28:06 29.94 18247
8:28:08 29.91 18324
8:28:10 29.92 18402
8:28:12 29.91 18483

Caustic Logic - is that a typo in there or do they really reset the altimeter to 30.21 then back to 29.91 after already setting it to 29.91??

[edit on 5-3-2007 by mirageofdeceit]

Neither. sorry for the long delay, i had to take a break and then I selpt way in. There's a perios of a few seconds there where the numbers fluctuate each time they're changed. That's the last residual of the initial 30.21 setting. Note I also included another 30.21 right blelow(above) the FLO18 threshhold to illustrate...

Yes, I can see your posts, but I was too tired to respond last night. You and Lear have some great insights and I'm glad this is turning into a proper research thread when it started as a stumble thread. In fat I'll be dome with my Qs soon, but there may be more wonderful/terrible things to find.

I think the hijacker reset deserves its own thread. I'll even let someone else take it up if they can beat me to it. And I'm in no big rush, a historian by training.

[edit on 5-3-2007 by Caustic Logic]

Originally posted by mirageofdeceit

time pressure alt (CLIMBING)

8:27:58 30.21 17938
------------------------------ FL018
8:28:00 29.91 18015
8:28:02 30.21 18093
8:28:04 29.91 18170
8:28:06 29.94 18247
8:28:08 29.91 18324
8:28:10 29.92 18402
8:28:12 29.91 18483

Caustic Logic - is that a typo in there or do they really reset the altimeter to 30.21 then back to 29.91 after already setting it to 29.91??

[edit on 5-3-2007 by mirageofdeceit]

Neither. sorry for the long delay, i had to take a break and then I selpt way in. There's a period of a few seconds there where the numbers fluctuate each time they're changed. That's the last residual of the initial 30.21 setting. Note I also included another instance of 30.21 above (below0 the FL018 threshhold. These are numbers from the AAL_77_tabular CSV.

Yes, I can see your posts, but I was too tired to respond last night. You and Lear have some great insights and I'm glad this is turning into a proper research thread when it started as a stumble thread. In fat I'll be dome with my Qs soon, but there may be more wonderful/terrible things to find.

I think the hijacker reset deserves its own thread. I'll even let someone else take it up if they can beat me to it. And I'm in no big rush, a historian by training.

[edit on 5-3-2007 by Caustic Logic]

[edit on 5-3-2007 by Caustic Logic]

Originally posted by johnlear


the recorded alt does not change at all with trim.

That is correct. Pressure altitude is recorded from the Air Data Computer and not affected by the altimeter setting on either the Captains or the F/O's altimters.

Hi John,

Does this mean that the altimeter in the cockpit should *not* "jump when the altimeter is set to 29.92? Or when it's reset to local barometric pressure?

Or should the altimeter jump? I.e., should the needle pop up or down when the altimeter is set or reset?

Thanks,

Originally posted by johnlear
What this all of this tells me is that whoever was flying this airplane was very experienced in flying the airplane and in using the autopilot. He knew how to make the airplane turn and descend using the autopilot. He knew exactly when to reset the altimeters and set them to barometric pressure of 30.24. He then disconnected the autpopilot and began hand flying at 7000 feet, and then flew a very precise profile into the Pentagon.

Hijackers? Not a chance. And who gave them the local barometric pressure of 30.24?

And if there was one pilot who set the First Officers altimeter?

And how could they be so focused to set the altimeters at exactly FL180?

And why would they reset the altimeters? They were going to crash.

Many questions. I’ll look into this deeper tomorrow.

Into or over the Pgon, right? There are these charges, supposedly also bolstered by this evidence... Also I've always entertained the possibility of remote control, but a lot of this activity is manual in nature. Were there trained, FAA-compliant pilots inside, or can these things be changed remotely? And if not suicide hijackers, how on earth would they have followed all FAA regs except the one about not crashing into buildings?
This is all oddd... and then the phone calls, etc but that's a tired game.

Sorry I keep doing double-posts today.

Mr lear, I'm not sure which collumn those readings are from. My file's hard to read. It's in there, and I guess you may be diggin thru it this very minute.

I'll be back with anything new i may find.


[edit on 5-3-2007 by Caustic Logic]

Odd is an under statement. I've been arguing for a rational explanation to all the discrepancies on another thread, and just today discovered the DFDR data. That discovery prompted me to discard a theory I was arguing. If the raw data in the the .csv files is authentic and accurate this whole thing makes no sense at all.

Why would a group of people capable of orchestrating the events of 9-11 create such a complex operation fraught with so many possiblities of error or discovery, and how could they have made such an enormous mistake as allowing this damning DFRD data to be released? I still have many questions about the data, which I will irritate everyone with over the next few days, however, so far, I see what appears to be a flight profile flown by very experienced pilot, setting the atimeter, going in and out of AP, and as JL asked, why would he bother getting and entering a local alt. setting, who would he have gotten it from? These questions assume the data is authentic and accurate, and I still have many questions on that account.



[edit on 3/5/2007 by darkbluesky]

Originally posted by darkbluesky
Odd is an under statement. I've been arguing for a rational explanation to all the discrepancies on another thread, and just today discovered the DFDR data. That discovery prompted me to discard a theory I was arguing. If the raw data in the the .csv files is authentic and accurate this whole thing makes no sense at all.

Why would a group of people capable of orchestrating the events of 9-11 create such a complex operation fraught with so many possiblities of error or discovery, and how could they have made such an enormous mistake as allowing this damning DFRD data to be released? I still have many questions about the data, which I will irritate everyone with over the next few days, however, so far, I see what appears to be a flight profile flown by very experienced pilot, setting the atimeter, going in and out of AP, and as JL asked, why would he bother getting and entering a local alt. setting, who would he have gotten it from? These questions assume the data is authentic and accurate, and I still have many questions on that account.
[edit on 3/5/2007 by darkbluesky]

Welcome to the thread Darkblue! Yes, sorry for sort of ignoring that, "who from" is a good question about the re-set. Unless the hijacker was in the cockpit on the way up and saw Burlingame turn the knob, saw 30.2 something turn to 29.92 at 18,000 feet, and guessed on 30.23 at 18,000 on the way down to "look normal' despite being hundreds of miles off-course with no transponder or comm in the midst of a terrorist air attack... not much for camouflage.

I'm just glad to have gotten this ball rolling. A good place to look is for comparitive pressure re-sets in the FDR "specialist's study" PDF. Is this parameter entirely omitted as unreadable in that? If not, then what does it say? (it's unreadable to me, so I'm the Q asker now). And if it is unreadable, how did it get in the tabular CSV file to not be mimicked in the animation?

And we're back to my first thoughts - why don't these sources match up?

[edit on 5-3-2007 by Caustic Logic]

Could you post a link to the FDR datas you are referring to please? I have two files here, one apparently the raw L3 code and another a CSV file, but not sure if I'm looking at the same data.

I'll see if I can read the L3 code; I'm surprised I could get it. I got it from one of your other links you posted above. I've yet to actually see if it is any form of FDR data at all, but it was a big download - 22Mb, so there is something there.

EDIT: Hmmmmm....... anyone know the data structure of L3 compressed FDR data? I thought this was proprietary??? If so, I won't be writing a decoder for it. I'll check this out tomorrow.

[edit on 5-3-2007 by mirageofdeceit]

Originally posted by nick7261
Hi John,
Does this mean that the altimeter in the cockpit should *not* "jump when the altimeter is set to 29.92? Or when it's reset to local barometric pressure? Or should the altimeter jump? I.e., should the needle pop up or down when the altimeter is set or reset?

The reading on the altimeter that is being reset in the cockpit will 'jump' or 'change' or 'pop up' or 'pop down' when the altimeter is reset.

Originally posted by mirageofdeceit
Could you post a link to the FDR datas you are referring to please? I have two files here, one apparently the raw L3 code and another a CSV file, but not sure if I'm looking at the same data.

I'll see if I can read the L3 code; I'm surprised I could get it. I got it from one of your other links you posted above. I've yet to actually see if it is any form of FDR data at all, but it was a big download - 22Mb, so there is something there.

EDIT: Hmmmmm....... anyone know the data structure of L3 compressed FDR data? I thought this was proprietary??? If so, I won't be writing a decoder for it. I'll check this out tomorrow.

[edit on 5-3-2007 by mirageofdeceit]

I'm not even sure which one the L3 is, no clues to help, sorry, good luck. You seriously need another link? All the links are in there, but mixed up. So one final time and organized, here are the sources I mean when I refer to:

- FDR "Specialist's study" (PDF) - NTSB link www.ntsb.gov...
Can also be found along with other NTSB-certified files at: www.ntsb.gov...

- Pilots link for AAL77_tabular (zipped CSV file) - P49T link 71.18.155.196...
If that link doesn't work, here's the page its linked from, along with another file of plotted parameters. z9.invisionfree.com...

That's all I've been looking at other than the animation, and that only in PBB. Sorry for any confusion.

Although I doubt the 'hijackers' would bother (as John points out, they're planning on flying into a building not shooting an approach to minimums) they could easily get the local barometric pressure by monitoring ATIS or any ASOS station in their vicinity or possibly by just monitoring any approach frequency. But again, why would they bother?

Originally posted by jtma508
Although I doubt the 'hijackers' would bother (as John points out, they're planning on flying into a building not shooting an approach to minimums) they could easily get the local barometric pressure by monitoring ATIS or any ASOS station in their vicinity or possibly by just monitoring any approach frequency. But again, why would they bother?

Right. And why bother to set the co-pilot's altimeter? Who was the co-pilot anyway?