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Pilots For Truth > American 77 > Fdr Vertical Speed

Posted by: johndoeX Oct 15 2006, 08:41 AM
We all know the Dept of Defense video shows an object going level across the lawn. So "debunkers" have tried to offer the theory that the FDR altimeter may be lagging due to pressure differentials. I have plotted the last few seconds side by side to address this issue based on the FDR data.

Please remember the following altitudes are from the csv file and reflect Pressure altitude. You need to add 300 feet to get the actual altitude of the aircraft.

09:37:42 AM 307

09:37:43 AM 239

09:37:44 AM 173

09:37:45 AM
09:37:46 AM

Between :42-43: seconds is a 4080 fpm decent. A typical normal descent for a jet aircraft with a professional pilot at the helm.

Between :43-:44 seconds is a 3980 fpm descent. Again.. nothing major for a professional in a jet aircraft. This is even considered "normal". A steep descent sure.. but nothing "abnormal". Abnormal would be in excess of 7000 fpm.

The total fpm descent rate from 42-44 is 4020 fpm. Definitely a good rate of descent, but not abnormal for a professional pilot. Hani, if he did have training as a pilot in Cessnas, would only be used to 1,000 fpm descents. But we already know Hani couldnt control a 172, so i have no idea how he would handle 4000 fpm without hitting the pentagon lawn.

A quote someone was helpful to point out about altimeter lag...

e) Hysteresis: This error is a lag in the altitude indications caused by the elastic properties of the materials used in the aneroids. It occurs when an aircraft initiates a large, rapid altitude change or an abrupt level-off from a rapid climb or descent. It takes a period of time for the aneroids to catch up with the new pressure environment; hence, a lag in indications. This error has been significantly reduced in modern altimeters and is considered negligible at normal rates of descent for jet aircraft.

Basically. The above quote is correct. That altimeters do lag. When you abruptly change altitudes. In other words, when you are level and quickly move the stick, you will see a lag in the altimeter momentarily. Then it catches up as your are in the descent. You will also notice most modern altimeters have reduced this lag and that it is negligible in modern jets (mainly due to static port design and computers installed on modern jets).

Another helpful quote from a training site I had found during a quick search (when arguing the lag issue). I used to actually teach this to new students when i instructed full time years ago in Cessna's and Cherokee's.

c. Lag in the altimeter.
(1) Make an abrupt pitch change and point out the momentary lag in the altimeter.
(2) Make small, smooth pitch changes and point out that the altimeter, for practical purposes, has no lag. .

Now we see in the animation descent that it was deliberate, smooth and not abrupt. The descent rate wasnt abnormal for a modern jet. Therefore... no lag. This may be the reason why Boeing, the NTSB and the FBI do not want to help us decode the additional FDR data to help us confirm that there was most likely no lag. However, the data still needs to be decoded. You would think if this additional data supported the official story, they would be stepping forward to decode it. They arent. Also, if the additional data does lend itself to altimeter lag, then the increased descent rate would have to be explained as it currently conflicts with the DOD video of an object level across the pentagon lawn.

Now, if this altimeter is lagging, which we see from the above quotes it shouldnt be, the descent rate will increase from its present data and will be in further conflict with the Dept Of defense video (The "5 Frames Video") showing a level object crossing the pentagon lawn. The above object, which the NTSB says is AA77, its showing a 4000 fpm descent rate for the last two seconds of data in its present form. The video shows it level across the lawn for the very last second (1:26-1:27 in the above video).

If the official impact time was at 09:37:45, that means that AA77 would have had to pull out of a 4000 fpm descent instantaneously and be level across that lawn. IMPOSSIBLE! If this aircraft was too high to hit the light poles (480 feet as noted in the current data provided by the NTSB), it would have more time/altitude available to pull out of this descent and overshoot the pentagon. Leaving a fireball in its wake while quickly exiting the area. Very possible.

If you account for altimeter lag, the descent rate is increased to more than 4000 fpm.

Something is rotten in Denmark.

Now we all know why Boeing and the NTSB do not want to explain nor decode the further data we have. It will only conflict further with the DOD video if they want to use the "lag" excuse. But we know from the quotes its improbable the altimeter showed lag.

Final conclusion, either..

A. altimeter is accurate via the 4 sources of information we have that match and conflicts with the official govt story regarding the light poles and DOD video.


B. The increased descent rate makes it that much more improbable (read: impossible) an object was able to be level across the lawn in the DOD video.

(I may add/edit for typos in the future on this post)

Posted by: johndoeX Oct 15 2006, 08:42 AM
The possible altimeter lag was calculated from a point where there isnt any lag (at normal speed below Vmo and almost level flight) to the end of data. It was ~5500 fpm descent for that period of time. If the altimeter was lagging at the end of data where it shows a 4000 fpm descent rate for the last second in its current state, lagging would mean the descent rate would be in excess of 4000 fpm. Concluding a further conflict with the DoD video which shows something level across the lawn...

user posted image

Now the argument is that the above video could show a descent even though it shows level with the lawn. And I agree. The gradient for the lawn and that section is roughly 300 fpm descent (43MSL at base of poles - 38 feet at pentagon base = 5 feet x 60 seconds = 300 fpm). Being that the above object is clearly level with that front lawn, it means that object at the MOST has a 300 fpm descent rate. That is in direct conflict with the 4000 fpm descent rate already shown on the FDR. The FDR recording stops just to the right of that camera view. In other words, where the FDR stops, the DoD video begins. They conflict.

Posted by: johndoeX Oct 15 2006, 08:42 AM
FDR stops here, just above the highway in a 4000 fpm descent.

user posted image
(edit: also note the right bank angle. That also conflicts with the official story that the aircraft needed a left bank angle in order to account for the generator damage. The right bank angle is recorded in the FDR up till reported impact time of :45).

user posted image

DoD video begins here, just as it crosses the highway level across the lawn with a 300 fpm descent gradient.

user posted image

They conflict.

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