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FDR Vertical speed, Altimeter lag issues addressed as well.

rob balsamo
post Sep 10 2006, 11:30 PM
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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.

Altitudes are in bold. 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)
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rob balsamo
post Sep 10 2006, 11:31 PM
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Also keep in mind, IVSI or Instantaneuos Vertical Speed Indicators (also in same articles quoted above) are on most modern aircraft/jets which virtually eliminate lag. The VSI is the most "laggy" instrument on any airplane. They add certain mechanisms inside the instrument to eliminate this lag problem associated with most primary aircraft with primary basic instruments.

Most beginner aircraft do not need highly sophisticated equipment to deal with lag as everything happens rather slowly in primary trainers.

As noted in the above post, modern equipment on jets eliminate lag.

Hope this clears up the lag issue for some of you. Feel free to ask questions. (Spin and trolls not welcome).
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