AAL77

On Sep 11, 2001, American Airlines Flight 77 was one of 4 aircraft hijacked. It was subsequently utilized as a weapon of mass destruction as it was flown into the Pentagon. At approximately 8:56 a.m. EDT, while in Indianapolis Center (ZID) airspace, cruising at FL350 (approximately 35,000 feet above sea level), the transponder was simply turned off. Normally, disabling a transponder does not make an aircraft invisible to air traffic controllers, as the high-altitude Center controller need only select the “ALL PRIM” (all primary) filter to view the aircraft’s SEARCH radar (i.e. “primary” aka “skin paint”) targets. As a matter of fact, Chuck Thomas, the radar controller who was working AAL77, selected the ALL PRIM filter within one second of AAL77’s datablock displaying “CST” (Coast Mode...which indicates that the aircraft’s datablock is no longer being updated with radar data). The disturbing thing is, there was no primary target on AAL77 available for Thomas. AAL77 ultimately flew the entire way back to its impact, some 41 minutes later, unnoticed by Air Traffic Control.

Key 9/11 Commission findings about radar data processing: On page 25 (pdf pg 42) of THE 9/11 COMMISSION REPORT, they write “The reasons are technical, arising from the way the software processed radar information, as well as from poor primary radar coverage where American 77 was flying.” Footnote 142 (pg 460...pdf pg 477) states “142. Primary radar contact for Flight 77 was lost because the “preferred” radar in this geographic area had no primary radar system, the “supplemental” radar had poor primary coverage, and the FAA ATC software did not allow the display of primary radar data from the “tertiary” and “quadrary” radars.”

Comments on above findings: The above findings by the 9/11 Commission help to shed light on the fact that even though an aircraft may be detected by radar, that aircraft may not necessarily appear on the air traffic controller’s display. My emphasis for over the past two decades has been on the low-altitude aspects of this unsatisfactory condition, where even an aircraft with a perfectly working transponder, that is properly replying to interrogations, can be invisible to the air traffic controller (learn more about my criticism of multiple radar data processing here).

I feel that the 9/11 Commission was not able to dig deep enough into the radar picture concerning AAL77, otherwise they wouldn’t have stated that there was “...poor primary coverage where American 77 was flying.” AAL77 was over southern Ohio at the time the transponder was disabled, and being approximately five-and-a-half miles high, there was considerable overlapping coverage from surrounding Air Route Surveillance Radar (ARSR) sites that do (or could) feed to Indianapolis ARTCC (ZID).

Those long-range radar sites, their distance and direction from AAL77 at the time the transponder was disabled, and a graphic depicting the relationship of AAL77’s return flight with respect to those individual ARSR sites, are available below. [A special thank you to Glen H Schulze <contact>, who provided the “picture is worth a thousand words” graphics.]

London, OH...................QWO...79 nm north-northwest..see AAL77_QWO_ARSR_Schulze.jpg

Lynch, KY....................QRI..105 nm south............see AAL77_QRI_ARSR_Schulze.jpg

Oakdale (Pittsburgh), PA.....PIT..158 nm northeast........see AAL77_PIT_ARSR_Schulze.jpg

Brecksville (Cleveland), OH..QDB..165 nm north-northeast..see AAL77_QDB(CLE)_ARSR_Schulze.jpg

Bedford (Roanoke), VA........QBE..167 nm east-southeast...see AAL77_QBE_ARSR_Schulze.jpg

Indianapolis, IN.............IND..177 nm west-northwest...see AAL77_IND_ARSR_Schulze.jpg

Maiden (Charlotte), NC.......QRM..197 nm south-southeast..see AAL77_QRM_ARSR_Schulze.jpg

Thomas G. Lusch

June 10, 2010

P.S. Miles Kara, professional staff member of the Congressional Joint Inquiry and the 9-11 Commission, served on Team 8. He continues his interest. Learn more here.