AAL 77 Navigation System Activity

Figure 3 shows the VOR stations tuned to by the two VOR receivers on American Flight 77.  The EFIS mode determines the type of display shown on the EHSI. During the initial part of the flight, the EFIS is in “MAP” mode.  In this mode, the EHSI displays an airplane symbol pointed towards the top of the display, with the magnetic heading and track shown in a partial compass rose at the top of the display.  Various points of interest - VOR stations, fixes, airports, and so on - can be displayed in their correct position relative to the airplane. The planned and projected route of flight can also be displayed in the MAP mode.  The range of the MAP mode can be adjusted from 5 miles to 160 nautical miles, depending on the detail or scale of map required.  At about 09:08:20, the display switched to VOR mode; in this mode, the EHSI displays the airplane’s  angular deviation or position relative to a specified radial from the selected VOR.

The points during the flight at which the VOR receivers were tuned to new frequencies are shown on the map in Figure 2 as yellow diamonds. The points shown occur after the hijackers took control of the cockpit. Lines from the airplane flight path to the stations indicate the VOR stations tuned by the left and right VOR receivers. The point on the flight path from which the lines originate are the points at which the station was first tuned, i.e., the points at which the VOR station frequency selected by each receiver changed.

Note that while the EFIS was initially in MAP mode, the left and right VOR receivers were tuned to stations whose bearings from the airplane differed by about 90 degrees, at the time at which the VOR station pairs were changed. This illustrates the method the system uses for obtaining VOR position fixes to update the INS.

During the turn back to the east, the frequency of the right VOR receiver was set to 111.0 MHz, corresponding to the VOR station located at Washington Reagan National Airport (DCA). At the time the DCA frequency was selected, the station was too far away for its signals to be received by the receiver.  The right VOR receiver remained tuned to the DCA VOR for the remainder of the flight, except for a 1-minute period at 9:15. The left VOR receiver was tuned to various frequencies, but was tuned to 113.5 (AML in Herndon, VA near Dulles Airport) at approximately 9:08. At approximately 9:18, the left distance measuring equipment (DME) began receiving information from the AML VOR. After receiving the DME signal, the airplane remained on a constant heading towards the Washington area.  At 9:32, both VOR receivers were tuned to the DCA VOR. 

Thats not exactly correct UT... its actually closer to the pentagon when you incorporate slant range. I have a clip of what im talking about if you want it. It was going to be in PBB2, but i wanted to keep the film to 1 hour. I may add it to the extras in the future.

When measuring to the northern path.. 1.5 DME off DCA VOR is exact in terms of the NTSB CSV file that it was recorded in the :43 frame. They match perfectly with slant range, speed, distance.. etc.

When used on the south flight path.. they dont match.

what?


1.5NM is 9000 feet. Why do you use 9100 feet?


I worked it out one day and IIRC, using the numbers directly from the NTSB at the proper time stamps, the distance over the ground is ~8900 with a 9000 feet slant range. (you cannot have more than 9000).

Basically, when calculated with speed and using the time stamp from the csv file, that distance puts you directly north of the citgo gas station as reported by Two Pentagon Police Officers and a gas station worker in ThePentaCon.