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Flight AA77 on 9/11: New FDR Analysis Supports the Official Flight Path Leading to Impact with the Pentagon
Frank Legge, (B.Sc.(Hons.), Ph.D.) and Warren Stutt, ( B.Sc.(Hons.) Comp. Sci.) January 2011
The course of the plane as determined by radar12 and the course calculated from the FDR are strikingly similar. This supports the view that these are reporting the same plane.
Flight course and final manoeuvre
In the following image (Fig. 1),14 it can be seen that impact with five light poles not only establishes the track through the damaged area, but also provides evidence that the wingspan of the plane, if it was a plane,15 is consistent with that of a Boeing 757, 124 feet 10 inches.16
If the position of the aircraft is plotted using latitude and longitude from the fully decoded FDR file, it becomes apparent that the course obtained is over 200 feet from the course defined by the trail of damage. A method for correcting the position reports was devised, which is described below.
The 757/767 Flight Management System (FMS) does not fly via the IRS unless it has nothing else to use, i.e. long overwater operations.
The IRS position begins to drift from the moment the system is initialised. One of the procedures I had when flying the aircraft (767) was to do a "quick alignment" towards the end of the flight preparation procedure. This was an acknowledgement that the initial datum would have moved during the preflight. (Turning the IRS's on was one of the first things you did when you started pre-flight checks).
The inertial position would be updated to the runway threshold automatically on the selection of take-off thrust. This was the last time during the flight that the IRS position would be accurate.
So how did the aircraft navigate accurately? The aircraft derived its position from a variety of navigational inputs into the FMS. The most accurate of these is GPS, which was not fitted on the 767's I flew till late in the production run and apparently not on AA77 either, followed by DME (distance measuring equipment), VOR's ( a radio Nav beacon) Localisers which are another form of beacon used in the Instrument landing system) and finally the IRS position.
As the aircraft flies, it checks and cross references all these navaids and derives the most accurate position. This is known as the FMS position.
So the IRS position would have been drifting from initialisation till takeoff, and then till the crash. This is why errors are apparent and why they don't mean anything. Anything meaningful in the report should refer to the FMS position, not the IRS position.
Gopher 6 took off from Reagan airport minutes before impact.
originally posted by: firerescue
a reply to: Salander
The maneuver supposedly made by Hanjour was impossible
January 2001 Hanjour took course in piloting a jet airliner in a simulator at JET TECH in Mesa Az
Hanjour already had a pilot license with a commercial rating
His instructor signed off the section for "TIGHT TURNS" ........
originally posted by: Jesushere
waypastvne What debatable here where you place the plane on the North or South side of the Navy Annex?
North side 60+ 10 = 70
South side 60+ 10= 70
The FDR has the plane on the North of the Navy Annex they must have placed the plane there based on other data?
originally posted by: waypastvne
a reply to: neutronflux
Hall effect sensor within the magnetic field of the compass.
The heading indicator, also called a directional gyro, is an instrument used to determine aircraft direction to aid the pilot in navigation
When set properly, heading indicators indicate primary heading and indirect bank (due to heading change)
Functions using the vacuum system and operates on the principle of torque-induced precession (gyroscopic precession)
Although very reliable, a magnetic compass has so many inherent errors, such as magnetic dip, that it has been supplemented with gyroscopic heading indicators
The heading of the aircraft is shown against the nose of the symbolic aircraft on the instrument glass, which serves as the lubber line to display directional (heading) information in reference to 360°
A flight management system (FMS) is a fundamental component of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern civilian aircraft no longer carry flight engineers or navigators. A primary function is in-flight management of the flight plan. Using various sensors (such as GPS and INS often backed up by radio navigation) to determine the aircraft's position, the FMS can guide the aircraft along the flight plan. From the cockpit, the FMS is normally controlled through a Control Display Unit (CDU) which incorporates a small screen and keyboard or touchscreen. The FMS sends the flight plan for display to the Electronic Flight Instrument System (EFIS), Navigation Display (ND), or Multifunction Display (MFD). The FMS can be summarised as being a dual system consisting of the Flight Management Computer (FMC), CDU and a cross talk bus.