9-11: Transponders and Ghosts; the search for AA 11

This brief article provides additional evidence that air traffic control was looking for AA 11 after the false report that it was still airborne and possibly heading for the nation’s capital.

Washington Area Ground Stop

On a conference call shortly before 9:24, Herndon Center directed a ground stop into the D. C. metro area; National, Dulles and Baltimore.  That action followed the determination, somehow, that AA 11 was still airborne.  I am not aware of any primary source information that documents that determination.

Here are the primary source voices, recorded at Position 14, Ops phone 5154 at Herndon Center. 092354 Ground Stop DC area

Radar and TSD Search

It is clear that someone a few minutes later, most likely Herndon Center, observed on a Traffic Situation Display (TSD) that AA 11, on its original flight path, was still in the system and was, according to Herndon Center, crossing the boundary into Cleveland Center’s (ZOB) airspace.  Herndon called the ZOB Traffic Management Unit and asked if they had the plane on radar.  ZOB checked; they did not.  That exchange also occurred at Position 14, Ops phone 5154.  092815 Herndon asks Cleveland about AA11

Note that this recording also confirms Ben Sliney’s order to ground stop everything, everywhere.  The time was just approaching 9:29.


The latter exchange is clear evidence that there were two AA 11 flight paths in the TSD system.  Recall that we established that a new track, AA 11A, had been entered to track AA 11 after it turned south in the vicinity of Albany, New York.  Conversations on tapes from New York Center (ZNY) verify that action.

It is clear from this Herndon exchange with Cleveland that the old flight plan was not removed from the system.  I recall that there was a later second call to a Midwestern Center, most likely Kansas City, posing the same question as was posed to ZOB.  I will add a link to that audio when I find it.

It has long been established that the primary source voice that announced the rebirth of AA 11 was Colin Scoggins at ZBW in a call to NEADS.  The conversations in this article show that Colin was not the only one who heard a reference to AA 11.

John Farmer and I believe, intuitively, that the false information concerning AA 11 was conflated from the report by Great Lakes Region that AA 77 had been lost.  We continue to work to resolve the issue.  My personal estimate, as I’ve voice in several articles, is that the FAA’s regional structure and its focus on incident and accident investigation, interfered with the Herndon counterattack that morning.

The Ghosts of 9-11: AA 77; a real ghost, still unseen; now looking for UA 175 (part 3)


In the previous two articles we discussed the approach of a primary only track, AA 77, into Dulles TRACON airspace.  We established that no one at any level was aware of the looming threat.  We also established that FAA’s Eastern Region, an administrative headquarters, was directing the air traffic control search for missing aircraft.

The Region prompted the ZDC manager to call his counterpart at ZID to look  for AA 77.  The ZDC manager then briefed his area supervisors that they were looking for limited data tag planes at altitude, specifically AA 77 and UA 175.  In this short article we will show that as late as 9:30 UA 175 was a matter of concern to Eastern Region.  AA 77 was not

Eastern Region

Eastern Region had jurisdiction over two of the four FAA Air Traffic Control centers involved on 9-11, Washington (ZDC), New York (ZNY), and it worked through them and their subordinate Towers and TRACONs to gather information.  For example, instead of calling Indianapolis Center (ZID) direct, the Region had ZDC call ZID to inquire about the loss of AA 77 over Indiana.

Concurrently, Eastern Region was trying to sort out what happened in New York City and was concerned with both AA 11 and UA 175.

AA 11

Here, we return, briefly, to a discussion of the most troublesome ghost on 9-11, the apparent rebirth of AA 11.  During interview, Ron Ruggeri, the Eastern Region Quality Assurance Staff Manager, stated he took the following action:

“[He] called the watch desk at ZNY, and was informed from Bruce Barrett that the impact was a terrorist event. Barrett checked a Situational Display per Ruggeri’s request to locate AA 11, and it showed AA 11 in Whiskey 105 but on a coast track (since the computer was searching for the target, and projecting its flight path).”

The Commission Staff was never able to pin down the source of the erroneous information concerning AA 11 but estimated it was derived from conversations on the Eastern Region telecon, an unrecorded conference.  Ruggeri’s mental picture of the track of AA 11 over water south of New York City supports that estimate.

Whiskey 105 is the military training area to which the Otis fighters were first vectored after takeoff.  Lynn Spencer in Touching History described it as “a military airspace training area over the Atlantic just south of Long Island.”

UA 175

Shortly after 9:29, Ruggeri called IAD to inquire about UA 175.  The call lasted less than a minute and IAD established that it did not have a flight plan in its computer for UA 175.  That conversation can be heard at this link. 1 IAD 27 DEPARTURE DATA Ruggeri Call 175

At no time does either Eastern Region or IAD make reference to the primary only track, the “no tag,” fast approaching the nation’s capital.

Google Earth

Here is the spatial position of AA 77 at the time of the Eastern Region call.  Permit me the irony to note that AA 77 flew just south of the ongoing construction of FAA’s Potomac TRACON facility; a new facility to solve known obsolescence and traffic control issues in the greater Washington DC area.

Location of AA 77 when Eastern Region called IAD about UA 175
Location of AA 77 when Eastern Region called IAD about UA 175


The time is now 9:30 and we have established that the primary only track later determined to be AA 77 is rapidly approaching the nation’s capital and no one has recognized the threat.  We have established that FAA’s Eastern Region is collecting information. There is no evidence of awareness at any level, including the White House that AA 77 is a looming threat.  At 9:30, AA 77 is  34 miles from the Pentagon, according to Google Earth.

A Preview of What’s up next

We will establish in a later article that, according to a second call to IAD, Eastern Region was in direct, near real-time contact with FAA Headquarters and was passing information along as it was received at Eastern Region.  We will also establish that AA 77 is not mentioned until after Danielle O’Brien and her supervisor sound the alarm.

The Ghosts of 9-11: AA 77; a real ghost, unseen (part 2)

Addendum March 22, 2010

The purpose of this addendum is to insert an audio clip of a conversation shortly after 9:25 between Herndon Center and Indianapolis Center (ZID).  Herndon initiated the call to learn whatever it could about the loss of AA 77.

Indianapolis reported that the aircraft was off radar and presumed lost.  ZID assessed that AA 77 was not involved in the World Trade Center events because the time of loss was at the same time as events in New York.

The Herndon Center caller assessed, based on time and distance factors that the most likely target in danger was the Sears Tower in Chicago.  The conversation can be heard here.  092506 Herndon and ZID discuss AA77

My Assessment

This conversation is clear evidence that FAA Herndon Center and, by extension, FAA Headquarters did not know that AA 77 was bearing down on the nation’s capital.  It is further evidence that Norman Mineta was clearly mistaken in his recall of events that morning.  There is no reasonable way that he could have known about AA 77.

At that time, 9:25, no one above the scope level at Dulles TRACON had any information whatsoever about AA 77.  Although two controllers spotted a “no tag” they had no idea what they had seen and information available at Dulles TRACON did not become actionable until 8 minutes later when the general alarm was sounded.

Original Article

In part one  we established that Washington Center, ZDC, was not looking for AA 77 as a primary-only target and never detected the plane.  Moreover, its conversation with Indianapolis Center about AA77 and its internal conference among area supervisors were not shared with Dulles TRACON, IAD.  In this article we continue the track of AA 77 and relate it to IAD using primary sources–air traffic control conversations, the flight data recorder, and radar files.  And we start with IAD, itself.


Dulles TRACON no longer existed by the time the Commission began its work.  In December, 2002, FAA commissioned  a consolidated facility, Potomac TRACON, which assumed the responsibilities of the TRACONs at Dulles, National, and Baltimore airports and Andrews Airfield to solve known air traffic inefficiencies and obsolescence issues as detailed in the linked document.

The Commission Staff toured both Dulles and National Towers and TRACONS.  Concerning the latter, we simply saw empty rooms at both locations.  To interview participants of the day we had to track them down wherever they were; several at Potomac TRACON, which we twice visited.

We determined that around 9:25 IAD did see, but did not recognize the threat posed by AA 77.  This is the IAD story and we begin with the first known primary source evidence.

See that no tag?

In the 9:25 timeframe a controller at the IAD South Departure position said: “see that no tag, there?”  A co-worker responded, “I do.”  The controller then said, “I’ll just flash him on to Wash or Center,whatever.”  The co-worker responded, OK.  That short six second exchange can be heard here No Tag.

It is speculative, but probable, that the controllers were seeing the track that was AA 77.  It is also possible that they were referring to something else entirely.  Given that it was AA 77 they did not recognize it as a threat and there is no evidence that the information was shared internally to IAD or that “Wash or Center” saw the flash.

According to the flight data recorder readout AA 77 was at 18,000 feet, technically just entering Class E airspace.  Whatever the technical division of air space responsibility no FAA facility recognized the threat.  Further, no one cued NEADS to look for that “no tag.”

FAA did acknowledge that early spotting of a “no tag” in its secondary source documents provided to the Commission.  We will consider those documents but first we need to talk about a second opportunity to see the AA 77 primary only track, this one by IAD South Departure and two ZDC Sectors, separately.

A Second IAD opportunity

In my Commission work I identified one plane that might have caused IAD (or ZDC) to recognize the approach of AA 77.  A graphic of the track of that plane, labeled M3 1531, is part of a series of slides concerning the approach of AA 77 and is inserted here, updated.

M3 1531 and AA 77

The two aircraft were separated vertically by more than 6000 feet.  AA 77 was just passing through 10,000 feet altitude into IAD designated airspace.  The point of spatial intersection was just West of Warrenton, Virginia.

In air traffic communications we first hear about M3 1531 around 9:26.  Dulles South Departure attempted a manual hand off of the southwesterly transiting aircraft to ZDC Casanova Sector.  That controller exchange can be heard at this link. M3 1531 Casanova Tape 19 side 1.

In a second attempt a minute later a different ZDC controller acknowledged “not that VFR guy.”  “VFR” in this context is not a reference to AA 77; it is a reference to a transponding aircraft.  IAD successfully handed M3 1531, who was VFR, off to ZDC, Azalea Sector.

At no time does any controller notice or comment on a primary only aircraft headed east. Here is the relevant conversation.   M3 1531 Azalea Tape 19 side 1 and M3 1531 Azalea Tape 19 side 2 It is in two parts because the transmission occurred at the end of one cassette tape and the beginning of another, as provided to the Commission and as archived by NARA.

Here is a Google Earth plot of the spatial intersection of AA77 and M3 1531 just West of Warrenton, Virginia.  As established earlier the two aircraft were 6000 feet apart in vertical separation.

Spatial Intersection of AA 77 and M3 1531
Spatial Intersection of AA 77 and M3 1531

I know of no other primary source air traffic control transmissions which relate in any way to the approach of AA 77.  To see how FAA treated this information we next turn to a discussion of FAA assessments in the aftermath.

FAA Assessments

To sumarize, FAA established a time of 9:25 in its early assessments.  That assessment held at least through September 18, 2001, as memorialized in the Administrator’s Briefing Book.

In later assessments, including a March 2002 draft report, the 9:25 time no longer appeared.  By then FAA had settled on a time that equated to IAD sounding the alarm to National TRACON/Tower and to the White House/Secret Service.

Retrospectively, FAA established that IAD controllers may have seen the primary only track as early as 9:25, but there is no evidence that IAD recognized the threat any earlier than 9:32.

A  FAA “Chronology of Events“, unattributed, but fax time-stamped “6:18AM SEP 12, 2001” demonstrates the confusion within FAA as to what happened.  A 9:25 entry states: “AAL77 Lost at 9:25AM York Kentucky.”  A 9:33 entry states: “DCA notified check Hotline activated; primary 3 miles south, now 1 mile.”  No mention is made of anyone noticing the track that would later be identified as AA 77.

The next day, in an internal summary prepared at 9:00 on September 13, 2001, FAA’s AAT-20 documented this information: “0856 Radar contact is lost.  No Further contact with aircraft.  Dulles ATCT [IAD] (bolding in original) 0925 (estimate) Controller observes primary target at high-speed transitioning west to east toward DC.  0933 Controller informs Operational Supervisor, whom in turns advises Washington National (DCA).”

That is an accurate statement, based on primary source information.  As we have established, a controller saw a “no tag” at 9:25 and did not recognized it as a threat.  The use of the word “controller,” singular, morphed into “controllers,” plural, as FAA prepared its Administrator for Congressional hearings.

That morphing from singular to plural was likely based on individual controller statements taken as part of FAA’s accident package preparation for submission to NTSB.  Retrospectively, individual controllers may have recalled that they did see the primary only track.

The fact remains, however, that none of them saw it as a threat and none of them alerted their supervisors.  That alert did not come until Danielle O’Brien recognized a problem; we will discuss that in a subsequent article.

The Administrator’s Briefing Book

As of September 18, 2001, at 5:20 PM the Administrator’s Briefing Book for Congressional hearings contained the following entries.  “0925:00 Between 0925:00 and 0930:00 (time is approximate based on personnel statements) – Several controllers at Dulles TRACON observe a primary radar target (unidentified but later confirmed to be AAL 77).”  “0933:00 (Time is approximate based on personnel statements – Dulles TRACON advises…Secret Service of an unknown aircraft heading in the direction of the White House…”

This version of the briefing book is the day after the White House meeting to discuss the events of the day and is likely the same version used by FAA representatives at that meeting.

The acknowledgment that the controller’s 9:25 observation may have correlated to AA 77 was dropped in subsequent FAA summaries.  An undated “Chronolgical Events at Dulles Tower on September 11, 2001,” contains this entry: “1332;20 (time approximate) Controller at Dulles Tower working the Final West position informs the other controllers in the radar room about the target observed moving estbound.”

Months later, in its 21 March 2002 draft report “The Air Traffic Organization’s Response,” the first mention of AA 77 as a threat is the 9:33 alert.

A Personal Comment

This look at FAA staff work in some detail does indicate that FAA was aware of all the relevant air traffic control tapes.  They went into the White House meeting with accurate primary source information.  I extrapolate from this that they knew, from their perspective, the actual notification times to the military.

I estimate they must have know the centrality of NEADS to the military equation.  They certainly knew there was no 9:24 notification time to NORAD concerning AA 77.  Whatever their position, it was subsumed at the White House meeting.

The Commission Report

The Staff wrote: “At 9:32, controllers at the Dulles Terminal Radar Approach Control “observed a primary radar target tracking eastbound at a high rate of speed.” This was later determined to have been Flight 77.”

At one time we considered a time of 9:25 but the convergence of information dictated a later time.  We concluded that 9:32 was the earliest time that situational awareness developed at IAD; they processed what they were seeing and then sounded the alarm.

Next Up

Before we turn to the awareness and subsequent alarm we will briefly examine a phone call between FAA’s Eastern Region and IAD in the 9:29 time frame.  Recall that we established that Eastern Region, an administrative headquarters, was dictating the exchange of information.  As a preview of the next article, Eastern Region called to inquire not about AA 77 but about UA 175.

After that we will turn to Danielle O’Brien and the actions she and her supervisor took.

The Ghosts of 9-11: AA 77; a real ghost, unseen

Addendum added February 6, 2014

My recall of the arrangement of transponder knobs on American and United planes, below, is not accurate. Here is what I wrote in November 2003 in Commission MFR 04017215.

“The transponders on United B757 and B767 airframes are identical. The transponders on American B757 and B767 are also identical and differ from the United version in a single detail. There are four knobs on the American version that change the transponder code. There are only two on the United Version [sic]. In both versions the knobs are stacked in groups of two. Therefore, there are two stacks of two knobs each on the American version and one stack of two knobs on the United version. In all cases the upper knob is smaller than and easily distinguished from the lower knob.” The following paragraph in the MFR is redacted, “9/11 Closed by Statute.”

Addendum added Nov 20, 2009

Here is a slide version of this  article.  Slides are timed and will advance automatically.  Included are screen prints of a Google Earth plot and data from the FDR, as well as a brief summary slide.  Embedded audio not yet active; working on it.

American Air Flight 77 ZDC ZID Slide Show

Original article

In my original “Transponders and Ghosts” article I wrote: “Plane by hijacked plane, each transponder manipulation presented a different problem set to air traffic control, to managers of the National Airspace System and ultimately, to the National Command Authority.”

To briefly summarize, the four transponders on the hijacked airplanes were each manipulated differently.  Three were turned off at distinctly different times in the flight paths of those planes and a fourth, the transponder on UA175, was changed to a different code.

We now have more insight into the problem that latter manipulation caused.  I hasten to add that we have no direct knowledge of the hijacker tactics concerning the transponders; what we do know is that retrospectively the tactics, planned or serendipitous, were effective.

AA77, itself a ghost

At 9:18 the Operations Supervisor at Washington Center, ZDC, Cary Johnson, called Indianapolis Center, ZID.  The call can be heard at this link. ThomasJohnson He reported that he had observed on TSD (Traffic Situation Display) that AA 77 was a ghost somewhere over Indiana and asked if ZID was working the aircraft.  The Operations Supervisor at ZID, John Thomas, told Johnson that AA 77 had been reported lost but may have turned around and was heading somewhere else.

During the course of the conversation the two managers established that they were looking for an aircraft at last altitude of 35,000 feet, and that ZID had initiated rescue procedures.


After concluding the ZID call Thomas convened a conference call with his Area Supervisors; that conversation began shortly before 9:22 and lasted less than one minute.  The call can be heard at this link.  johnsonarea They agreed they were looking for an aircraft with a limited data tag and one with a transponder code change.  The reference was to AA 77 at 35K feet and UA 175 over New Jersey at 31K feet.

UA 175

In the “Ghosts” article we established that concurrent with the impact of AA 11 into the North Tower the transponder code on UA 175 was changed, and then changed again.  The code was first changed to 3020 and then to 3321.  There is a logical explanation for that sequence.

When the Commission Staff visited the “Companies,” American and United Airlines, we were provided in-cabin and in-cockpit orientations on both B757 and B767 aircraft at each Company.  While in the B767 cockpit with the United senior pilot I had him show me the transponder and change the code.  His technique was a two-step sequence.  On the first step he changed the first and third digits, the second and fourth defaulted to zero.  On the second step he changed the second and fourth digits.

At the time, United transponders had four knobs in two stacks of two each.  The American transponders had four separate knobs.  [See addendum of February 6, 2014 at the beginning of this article.] In retrospect, that is my best explanation for why the transponder code on UA 175 changed, and then changed again.

Among others,  FAA’s Eastern Region knew of the code change and it was Eastern Region, not Herndon Center that was advising the air traffic control operations managers.  We will return to that point later, but first back to ZDC.

ZDC, Continued

At no time did ZDC managers and supervisors discuss or did Johnson direct activating the primary switches on their scopes.  ZDC never looked for and never recognized a primary only target approaching the nation’s capital from the west.  By then, it was too late.  The time was approaching 9:23 and a very real ghost, AA 77 was upon them and had begun a descent, not from flight level 35, but from flight level 25.

AA 77, Flight Data Recorder

According to the flight data recorder, a primary source,  AA 77 left 35000 feet altitude at 9:01 soon after the hijackers took over.  By 9: 14 it was at flight level 25,000 and remained there during the course of the air traffic control conversations between ZDC and ZID and among the area supervisors at ZDC.  About 9:22 it began its final descent and by 9:29 it was below 10,000 feet altitude.

Given that primary source data and given the instructions the ZDC operations manager passed to his area supervisors, ZDC had no chance to detect AA77.  Moreover, it was quickly moving into IAD (Dulles Tracon) air space as we shall see by considering another primary source, radar files from the 84th RADES.

AA 77, radar track.

NEADS radar reacquired AA 77 shortly before 9:10, but as a primary only track.  Moreover, as opposed to the situation with AA 11 where NEADS could have determined altitude it could only have done so for AA 77 during the period 9:16 and 9:27 while the Oceana Radar was acquiring the aircraft.  Thereafter, the  radar feed was coming from The Plains, Virginia, the only radar in the Joint Surveillance System that could not provide altitude information on a primary only track.  Shown here is  a Google Earth plot of 84th RADES files from The Plains radar for the period 9:18 to 9:28.


According to the plot, AA 77 was just approaching Virginia, west of Harrisonburg, while Thomas and Johnson were conversing, and was passing north of Harrisonburg and crossing I81 while Johnson was conversing with his area supervisors.  At the same time, after crossing the mountains, Hani Hanjour began the descent from flight level 25 headed for air space controlled by Dulles TRACON, IAD.

We will address the IAD story later in a separate article.  For now we need to document what is and is not happening in the hunt for AA 77.

Observables in real time

First,  at no time do either Thomas or Johnson talk about or consider NEADS or military assistance.

Second, they are not taking their cues from or responding to Herndon Center.  ZDC is responding to FAA’s Eastern Region, an administrative headquarters.  Recall that we established in a previous article that the two entities fighting the battle (second article at link)  that morning were NEADS and Herndon Center.

Third, at no time do Johnson and his Area Supervisors mention Dulles TRACON; they are concentrating on their mission which is handling transponding aircraft at high altitude.

Finally, ZDC does not turn on the primary switches on its scopes; instead they are looking for a limited data block, as was the case with UA 175.  I made a separate, final trip to ZDC on the very point of primary switches to confirm that they did not turn them on.  They did not.

A personal comment

We will likely never know the attack plan, in detail.  What we do know is the Atta and al Shehhi had extended periods of quality time together, measured in days, weeks, even months, to discuss ‘what-ifs’, do research, and speculate what might and what might not work as they finalized the battle plan.

Certainly they had sufficient time and the means to determine that a transponder turned off over West Virginia might cause problems; to determine that a transponder changing codes might also cause problems; and that a low level approach to the nation’s capital might escape detection.

Given the primary source information, including the flight data recorder data, we can reverse engineer Hanjour’s actions and make some informed observations.  First, Hanjour immediately changed altitude after takeover and turn around.  Second, he flew erratically for several minutes after reaching his new altitude of 25,000 feet.

That erratic flight reinforces the belief by some that Hanjour and the other hijack pilots were unskilled.  Conversely, it also reinforces the belief by others that the plot was planned in detail and was sophisticated.  It is plausible that Hanjour flew erratically to encourage the passengers to stay seated and belted.  Either way, Hanjour did level the plane and it flew smoothly at flight level 25 until it came time to descend.

It is a technicality of course, but during the period 09:24 to 09:27, AA77 was in Class E airspace, between 18,000 and 10,000 feet, airspace that ‘belonged’ to neither ZDC nor Dulles TRACON.  Even so, Dulles TRACON controllers did ‘see’, but did not recognize the significance of a ‘no tag’ approaching during that time.  And that’s the next story to be told.

Future articles

As mentioned, I will continue the primary source analysis of the approach of AA 77 through Dulles TRACON airspace and will establish using primary source information the earliest that the NCA would know it had an immediate problem.

It is also appropriate that we now queue up a discussion of Norman Mineta and his testimony.  It is clear from this article that as of 9:20, no one knew where AA77 was or that it was approaching the nation’s capital; not ZID, not ZDC, not IAD, not Herndon, not the FAA Eastern Region and, above all, not FAA Headquarters, NEADS/NORAD, the NMCC, Richard Clarke, Norman Mineta, the Secret Service or the Vice President and President.

It will be the initiative of one person, Danielle O’Brien, that anyone, anywhere, will have actionable information.  By that time, AA77 will be “inside the Beltway,”  a term that used to enjoy a certain cachet.

The Ghosts of 9-11, the transponder story

Addendum August 17, 2009

Relevant Commission work files recently became available.  Information concerning AA11A is modified accordingly.  My notes taken while reviewing a replay of TSD tapes at Herndon reveal that  “0844 11A pops up” and 0851 11A disappears 290 FL 291 GS.”  This information is secondary source information; the TSD tapes themselves are the primary source information.  The disappearance of AA 11A from TSD supports a Commission Staff working hypothesis (still our hypothesis to this day) that emerging information from Indianapolis Center about the loss of AA77 was conflated with continued uncertainty about the whereabouts of AA11 and the fact of a plane missing in the system became AA11.  It is important to remember that American Airlines, itself, was confused at the same time and thought both AA 11 and AA77 impacted the WTC.  This time frame is one of the chaotic moments of 9-11 and I will have more to say about that as I continue my chaos theory discussions.

Original Article

Air traffic control reactions to hijacker tactics created two significant ghosts on September 11, 2001. The ghosts were American Airlines (AA) 11A, the southerly track of AA 11, tagged by Boston Center in order to follow the first plane hijacked, and United Airlines (UA) 93, a new flight plan entered by Cleveland Center to allow Washington Center to follow the last plane hijacked. Those air traffic control actions were not passed in any form to FAA management outside of air traffic control, the Department of Transportation, and, by extension the Department of Defense and the National Command Authority. The actions taken were the result of a hijacker tactic to exploit the transponders differently on each of the hijacked aircraft.  (Added July 18, 2009)  The use of the term ‘ghost’ has no relationship to the air traffic control term ‘coast.’  ‘Coast’ is a specific air traffic control term to define a scope track no longer associated with data from an aircraft.  It disappears from a controller’s scope after a few radar sweeps.  While AA 11A showed in ‘coast’ in the immediate aftermath of the impact into the north tower it wasn’t until much later that it became a ‘ghost.’ (end addition)

The strategic terrorist plan was to hijack fuel laden jets and fly them into buildings. One tactic used, once the cockpits were secured, was to manipulate the transponders. We know post facto each transponder was manipulated differently and each of the four manipulations presented a different problem to air traffic control and, separately, to the managers of the National Airspace System. We do not know, and will likely never know, the extent to which the hijackers planned the tactic used or the extent of their awareness of the problems the tactic would cause. We do know in retrospect the tactical plan, as shown in this chart:

Transponder Tactics
AA11 Turned Off before the turn to the target
UA175 Code Changed when AA 11 impacted the North Tower
AA77 Turned Off as the turn to the target began
UA93 Turned Off after the turn to the target

At this point we need to talk about what can be “seen” and what was “seen” by FAA and the Northeast Air Defense Sector, NEADS. Concerning FAA, we need to distinguish between air traffic control and management of the National Airspace System. The National Airspace System is controlled in one way and is managed in a distinct and separate way. En route air traffic control centers and local Traffic Control (TRACON) and Towers have scopes which display air traffic in near real time. Unless specific steps are taken to do otherwise, en route centers only follow transponding aircraft and are not concerned with primary radar returns.

NEADS also had scopes which displayed air traffic in near real time. NEADS radars, co-located with FAA radars but tuned differently, provided air defenders with information biased toward non-responding aircraft. NEADS controllers looked outward, away from land unless directed otherwise. To make their life simpler any transponding aircraft that departed from the continental United States was friendly, by definition. Even though both FAA and NEADS were monitoring air traffic in real time, their procedures and activities were fundamentally different.

All other concerned entities, including the FAA Air Traffic Control System Command Center (Herndon Command Center), FAA Regions and Headquarters, and the airlines, had displays which depicted the current state of flight plans entered into the National Airspace System. These displays were refreshed every minute or so. The display is called TSD, Traffic Situation Display. It is the display the FAA used to show the public how the density of aircraft in the sky decreased incrementally to near zero after the nationwide ground stop was ordered. The difference between what can be seen by air traffic control and what can be observed by all other interested observers with the capability is distinct and is what wittingly or unwittingly, the hijackers exploited. Plane by hijacked plane, each transponder manipulation presented a different problem set to air traffic control, to managers of the National Airspace System and ultimately, to the National Command Authority.

American Air flight 11 (AA 11)

Both Boston Center and New York Center made the conversion to allow their radar scopes to see AA 11 after the transponder was turned off. What air traffic control lost was the ability to determine altitude. Flight level 290 (29,000) would remain the last known altitude for AA 11 and would be the altitude specified in the scramble order for the air defense aircraft at Otis Air Force Base. In order to help everyone monitor the aircraft as it presumably proceeded to a long runway-capable airfield somewhere to the south, a new track (AA 11A) was entered into the system by Boston Center New York Center (changed Jul 22, 2009). However, the original flight plan for AA 11 was left in the system and it became a notional flight, a ghost itself, which ultimately “landed” in Los Angeles. What could be seen and what was seen prior to the moment AA 11 flew into the World Trade Center North Tower are depicted here.

0845 EDT
AA 11 No/No Yes/Yes No/No
AA 11A Yes/Yes Yes/Yes Yes/No

Air traffic control could not see and did not see AA 11 after the transponder was turned off and the new track was created. Entities watching a TSD could see and did see AA 11 continue to the west coast. Air traffic control could see and did see AA 11A so long as it was flying. Entities watching a TSD could see and did see AA 11A so long as the track remained in the system. So, at the moment of impact air traffic control lost the ability to “see” the real AA 11 (now 11A) and lost it. Entities watching a TSD could and did “see” the track, AA 11A, a ghost in the system. This point is critical and bears repeating. At the moment AA 11 flew into the World Trade Center North Tower it was lost to air traffic control and to NEADS. It was not lost to anyone with access to a TSD. The now notional AA 11A continued southbound. The long notional AA 11 continued westbound.

Things became exponentially confused at 8:46 a.m. when AA 11 ceased flying. The impact caused three things to happen; one spontaneous and two deliberate. Spontaneously, speculation started as to what hit the north tower—a helicopter, a commuter aircraft, a Boeing 737, or something else. Deliberately, flight AA 11A continued southbound as a notional ghost in the traffic display system. More ominous and also deliberately, the transponder code on UA 175 changed, and then changed again.

United Air Lines flight 175 (UA 175)

We may never know how the code change tactic was conceived, planned and carried out by Mohammed Atta and Marwan al Shehhi. What we do know is in the space of a few seconds two things happened, AA 11 ceased to exist and UA 175 changed its identity. Orchestrated or not, that was a remarkable tactical achievement.

New York Center was immediately presented with four problems—where was AA 11A, what hit the north tower, where was UA 175 and what was the squawking intruder, code 3321? What could be seen and what was seen, overall, is depicted here:

0846 EDT
AA 11 No/No Yes/Yes No/No
AA 11A No/No Yes/Yes No/No
UA 175 No/No Yes/Yes No/No
Code 3321 Yes/Yes No/No Yes/No

It is clear from this matrix that air traffic control and FAA administrative Regions and Headquarters were not seeing the same picture, nor was there any overlap, any common point of reference. Entities watching a TSD display could not see the transponding intruder, Code 3321, there was no associated flight plan. Air traffic controllers could see the squawking intruder, 3321, and they quickly equated this to be UA 175 and a probable hijack. Other than NEADS, entities outside the air traffic control system could only see the, now notional, flights AA 11 and UA 175 proceeding to the west and the also now notional flight AA 11A proceeding to the south. Air traffic control was seeing the real world. NEADS was seeing the real world but was not looking for either UA 175 or Code 3321, no one had told them. All others were seeing ghosts.

American Airlines flight 77 (AA 77)

A few minutes before 9:00 a.m. and not long before UA 175 struck the south tower the transponder on AA 77 was turned off, just as air traffic controllers observed the plane beginning to turn to the southwest. Even though Indianapolis Air Traffic Control center switched its scopes to observe radar only returns it could not find AA 77. The Center looked primarily to the Southwest since that was the direction the plane seemed to be heading. Even had they looked to the East they would not have seen it, the radar only returns were not presenting on Indianapolis scopes. Indianapolis Air Traffic Control Center assumed the aircraft to be down and it quickly initiated search and rescue operations and alerted local law enforcement.

We will likely never know why and how the terrorist plan directed tactics for AA 77 as it did. The AA 77 transponder was turned off in the worst possible place for air traffic control, and for the air defenders. The military radars did not cover the interior of the United States and the FAA’s own coverage in that area was sometimes problematic. Surely, Atta did not know that Indianapolis ATC would lose AA 77 completely but he must have estimated that a transponder turned off during a turn would present a different problem of some sort to air traffic control. And, demonstrably, it certainly did.

NEADS radar lost AA 77 just as the plane began its turn, but it didn’t make any difference, NEADS surveillance technicians weren’t looking and they had no reason to do so. FAA radar lost the plane a couple of radar sweeps later. It would be several minutes before either the FAA or NEADS radar would pick up AA 77 as a radar-only target, FAA first by a few minutes, but again it made no difference, no one was watching, certainly not Washington Air Traffic Control Center which could have but was not cued to do so. At no time did Washington Center reset its scopes to monitor radar-only planes; it never saw AA 77. What could be seen and what was seen at that moment are shown here:

0852 EDT
AA 77 Yes/No Yes/Yes Yes/No
AA 11A No/No No/No No/No

Note: in this updated version of December 8, 2011, I changed the TSD block for AA11A from Yes/Yes to No/No. It is now clear to me that the new track entered for AA11A was not a new flight plan that would have continued in the TSD system. Rather it was a data block that faded after AA11A (AA11, actually) impacted the North tower. Even so, as a faded track in the radar system and as a plane reported to have been south of Kennedy (airport), it still caused confusion.

AA 77 could have been seen on air traffic control scopes, specifically at Washington Center, but was not. While observers of any TSD could “see” AA 77 they could only see it as a ghost continuing its flight plan to the West. NEADS could have seen AA 77 somewhere over western Virginia, but did not know the aircraft was hijacked and was not looking for it.

As Indianapolis Air Traffic Control center and American Airlines were grappling with what happened a ghost, AA 11A, and a real plane, AA 77, were bearing down on Washington DC. At about 9:21 a. m. the ghost was “seen” and reported. At about 9:32 a. m. the real plane, AA 77, was spotted by an alert controller at Dulles TRACON who sounded the alarm. It remains undetermined how AA 11A and AA 77 became conflated. One explanation is that emerging information about the loss of AA 77 became merged with confusing information as to what happened in New York City and the new information of a third plane became not identification of AA 77 but re-identification of AA 11A. The most likely source of this misinformation is one of the administrative FAA Regions or somewhere at FAA HQ, itself. From wherever the source the information was heard by a traffic management specialist at Boston Air Traffic Control center and it was he who notified NEADS at 9:21 a. m. that AA 11, the first hijacked plane, was still in the air. A few minutes later, at 9:33, came specific reporting to Reagan National Tower and to the Secret Service that an unknown aircraft, AA 77, was approaching the National Capitol Region (NCR).

NEADS, heard the information at 9:34 and, frustrated that it was never able to establish a track on AA 11, was able to locate and track AA 77 and establish track B32 a few moments before impact, but not long enough to forward the information to NORAD.

United Airlines Flight 93 (UA 93)

The final ghost of the day was UA 93. By far, according to primary sources of the day–the radar, flight data recorder, and the FAA tapes–the poorest performing hijack pilot was Ziad Jarrah at the controls of UA 93. It may even be that he was supposed to turn off the transponder before he turned back, or even in the turn, both of which tactics make more sense, especially given what happened with AA 77. But he didn’t, he waited until well after the turn back to do so.

Whatever the hijacker tactic was supposed to be, Cleveland Air Traffic Control Center seldom lost track of UA 93 and when it did, only briefly. Cleveland Center was able to do what New York Center tried to do, use other planes in the sky to monitor the progress of UA 93. Cleveland constantly updated the FAA Herdon Command Center in near real-time and that Center immediately passed this information quickly and continuously to the FAA Washington Operations Center (WOC).

What is important to know for any discussion of UA 93 is that it was never a real threat to the National Capital Region and that the air traffic control side of FAA knew this, as did the FAA WOC. Yet, this very real and very explicit timely tactical information never made it out of the WOC to the White House or the NMCC in useful form. UA 93 went down at Shanksville at 10:03, as recorded and reported by multiple, independent sources. At its demise UA 93, itself, became a ghost.

This point about the uncertainty caused by the ghost UA 93 cannot be understated. Much of the confusion about the testimony and recall of Norman Mineta and the Vice President, the inability of NORAD and FAA to come up with agreed upon timelines, and the inability of NORAD to present credible testimony to the Commission, can be attributed to a ghost, a plane that did not exist.  Shortly before 10:00 a.m. Cleveland Center took the initiative to enter a new flight plan for UA 93 in the National Airspace System and in the process took out the old flight plan. Recall that in order to manage AA 11 New York Center left the old flight plan in and created, literally, a new airplane, AA 11A. Cleveland Center took a different approach and deliberately replaced the original flight plan to help Washington Center and told them they were doing so. At this point here is what could be seen and what was seen.

0958 EDT
UA 93 old No/No No/No No/No
UA 93 new Yes/Yes Yes/Yes Yes/No

This is the one time that air traffic control and viewers of the traffic situation display are seeing the same thing, up to a point. Observers of both systems knew that UA 93 had turned around, that it was headed for the National Capital Region, and where it was. NEADS neither saw nor looked for UA 93 because the first they heard was after it was down.

The simple act of replacing one flight plan for another in the system caused no problem for air traffic control but major problems for Traffic Situation Display observers, by this time, at least, now including the Secret Service. The congruence in what could be seen and what was seen by air traffic control and observers of the TSD system ended abruptly at 10:03 a.m. when the real UA 93 ceased to exist. Notionally, the new UA 93 flight continued as a believable threat to TSD observers unless they knew what Cleveland Center knew, Herndon Command Center knew, the FAA WOC knew, and four minutes after impact NEADS, and by extension NORAD, knew, UA 93 was no longer a threat.

Absent that necessary information, the TSD display allowed multiple entities to observe and report the progress of the ghost UA93 in either minutes or miles, take your pick. This is almost certainly the information that Norman Mineta recalled as pertaining to AA 77 but actually the ghost of AA 11 UA93 (corrected August 12, 2009) : right information, wrong ghost, and wrong time.