I will attempt to explain why the animation is so critical. The fdr and csv files are altered in heading and coordinates (latitude and longitude). This is a FACT, and is not even open to debate anymore. The lingering questions surround at what point the alterations were made in the flight path. The animation is the result of physical parameters such as velocity, acceleration, and other established engineering parameters. It obviously does not care what the heading is set at or whether someone has changed it or not. Also, the animation was not sent to all of the FOIA requestors, but to only one individual. This leads me to believe that it was an inadvertent disclosure (or something else I won’t discuss at this time).
My readers will recall that I plotted one of the physical parameters, acceleration versus one of the suspected changed parameters, heading. The results were consistent with alteration. The correlation that indeed exists for the parameters do not intersect the origin of their graph (0, 0) as would be expected (fdr file) for a normal population. Instead, the data is offset to the upper right and the lower left quadrant is sparsely populated for the first half of the flight path and virtually empty for the later half. To someone like me that is VERY significant, but I wanted to wait for the full animation to verify my suspicions. Indeed I have verified that the animation represents the “real world” and the data files do not.
I will refer my readers to a previous post on magnetic heading and the corrections required to get TRUE heading. Just remember as I walk through the animation, subtract 10 degrees (approximately) from the display (magnetic) heading to get the “true” heading.
external image
This frame is right at take-off from Dulles while Flight 77 is still over the runway. I would ask that the folks at P4T correct me in comments on any misconceptions that I may have about aviation stuff. What follows is my understanding of flight stuff based on more of an engineering perspective than that of a pilot. I have indicated the magnetic heading indicator which at this point reads 300 degrees. It is known that the runway at Dulles is oriented to 290 degrees. This enables me to verify that everything is good up to this point and the animation agrees with the fdr and csv file headings. It appears that the indicator is pulling the value stored in the fdr file for display. Also important to note is that the controller is giving AA77 the heading (270 degrees) it is to change to. I noticed that for most major changes in heading there are similar instructions EXCEPT at a critical point I will note later. The time is in GMT, so subtract 4 hours to get EDT.
external image
In this frame, AA77 has completed the turn to 270 degrees. Note the black lines that form a grid on the “ground”. They represent latitude and longitude lines and a heading of 270 degrees would be due west and parallel to the grid lines. However, the TRUE path along the ground is to the left and angled (260 degrees) relative to the latitude lines. This is exactly what would be expected if the heading matches the animation (which it does at this point). Now note the turn ahead. I also find it curious that the fuselage of the model lines up with a “true” heading of 270 degrees while the ground path lines are definitely indicating a true heading of 260.
The first thing I noted as odd was there was no clearance from the controller to make the turn. If there was, then it would be a matter of just comparing the controller instructions to the actual heading. What is important to note is, about halfway through the turn, the magnetic heading is still at 270 degrees when obviously the heading has changed. The true heading at this point is at about 270 degrees (parallel to the ground line), during the first half of this turn, the magnetic heading value was “trimmed” by 10 degrees.
I confess a little ignorance at this point. I’m not sure if the controller requesting a heading of 270 means “magnetic” or “true” heading. The end result is a true heading of 270 degrees. Regardless, the initial turn on departure has a true heading of 260 and a magnetic heading of 270. The magnetic heading remains relatively stable at 270 while the true heading changes by 10 degrees to match it during this interval.
external image
In this frame, AA77 has completed that turn and is on a straight flight path. The heading indicated is 279 degrees which should represent a true heading of 269 degrees, or almost parallel to the ground grid lines (latitude). Clearly that is not the case. The magnetic heading indicator now indicates true heading and there is NO correction. Recall that the animation flight path is derived from the physics information and the most likely the magnetic heading is what is stored in the fdr file. What I believe to be the case is that the heading data in the fdr file has been “trimmed” by 10 degrees.
external image
This is confirmed at a point later in the flight path when the true path parallels the ground grid lines and the heading indicator reads 270, which is equal to the true heading.
external image
At the end of the first half of the flight path, the magnetic heading has been “trimmed” by 10 degrees. The magnetic heading and true heading are approximately the same at this point.
external image
After the turn back east, the “trim” has remained unchanged. At a heading of 90 degrees, the true heading is indeed due east (90 degrees) and parallel to the ground grid lines. I must note however that in the previous lengthy interval the true heading appears to be a few degrees greater than 90 degrees.
external image
(snip for space)
The folks at P4T have noted most of this already. My purpose was to see if the shift in the physics parameters versus heading parameters could be accounted for in the animation. I feel like they have been. Although the 10 degree heading “trim” is subtle in the final “turn” maneuver, the “trim” at the beginning of flight at 8:21:35 is downright blatant. An obvious 10 degree turn is made with NO evident change in heading (except to fluctuate between 270 and 271). I find it extremely curious after reviewing the United 93 controller transcript that giving heading via radio seems rather common, but in the case of AA77 the only heading given is the initial 270 heading. Later communications which refer to heading are ambiguous “turn 10 degrees right” or something to that effect. The obvious omission of such information in the controller transcript which could be used to verify heading elements strongly suggests to me that the controller transcript has been edited.