Aircraft identity

[gravity32]

I am trying to determine the identity of an American Airlines plane from FDR data. The file was created in Sept 2001. The A/C NUMBER is 35. The FLEET IDENT is 1. The file was recovered from the crash site. Can anyone help?

[grounded27]

You need to know what data form the fdr was in (Bits). What is your interest?

[gravity32]

The data has already been interpreted using the Data Frame Layout as follows:

A/C NUMBER appears several times because each bit is listed as a separate parameter. LSB means least significant bit, LSB + 1 means second least significant bit, LSB + 2 means third least significant bit etc. MSB means most significant bit. As you may know, a bit can be one of two values 0 or 1. For the A/C NUMBER we have:

A/C NUMBER LSB = 1
A/C NUMBER LSB + 1 = 1
A/C NUMBER LSB + 2 = 0
A/C NUMBER LSB + 3 = 0
A/C NUMBER LSB + 4 = 0
A/C NUMBER LSB + 5 = 1
A/C NUMBER LSB + 6 = 0
A/C NUMBER MSB = 0

Combining these bits in order with the MSB on the left and the LSB on the right gives 00100011. Converting this number from binary to decimal gives 35.

You may have guessed that this file has been provided by the NTSB, reportedly from AA77 which crashed into the Pentagon. My interest is that there are people who argue that this file is not authentic. If the explantion of the decoding above is correct the numbers 35 and 1 will not be in doubt. What some people dispute is that the numbers 35 and 1 confirm that this is the right aircraft. Is there a way to confirm the identification?

[grounded27]

Ok, 8 bit binary. Sorry mate you would need company inside info to determine the codes they assign to their aircraft. With hundreds and sometimes thousands of recycled tails AA001 does not equal 00000001, shot in the dark brother.

[gravity32]

Yes, tail numbers are recycled, however only one plane would be using a particular number at a spcific time. The number in question is of course N644AA.

Surely somebody knows somebody who could check it out.

[gravity32]

Thanks MikeEcho,

Unfortunately that video is now out of date. It refers to height discrepancies between the released FDR file data, in the form of a CSV file, and the observations of the plane hitting the light poles and the Pentagon. It also refers to a discrepancy between the angle of approach of the plane in an animation and the track angle observed in the damage.

It has now been shown that the last frame of data was missing in the CSV file given to the public. This frame has now been decoded (http://www.journalof911studies.com/volume/2010/Calibration%20of%20altimeter_92.pdf) from the raw data file and the Radalt shows the plane descending and hitting the light poles and the Pentagon, exactly as reported by eyewitnesses and as seen in the damage. There is thus no longer any discrepancy about height.

There never was a discepancy in the file regarding direction of approach as the file track angle corresponded with the damage track angle. The discrepancy was between the file data and the animation. It appears that a conversion error was made in construction of the animation. It is interesting that while the animation depicts the plane at the wrong approach angle, the compass shows the plane is at the right angle, strongly suggesting a mathematical error. The NTSB has said the animation was not used in any official procedure.

Unfortunately there are people who insist that the FDR file is not authentic. One of their complaints is that there is no ID of the aircraft in the file. There is of course ID in the file. The trouble is that it seems very hard for the public to confirm that the ID reported is for the right aircraft. Somewhere there must be a file which relates the reported ID numbers to a tail number. How can we find it?