Wednesday, March 7, 2012

Ed Ballinger and the uplink sent to United 175 at 9:51 EDT

Posted by Sergio

As known to many 9/11 researchers who dealt with the ACARS issue, Ed Ballinger, the United Airlines flight dispatcher in command for all United's East to West coast flights on the morning of 9/11, sent an uplink message to United 175 at 9:23 EDT, twenty minutes after the alleged crash of the aircraft against the South Tower in New York. This is a widely known and officially recognized fact. Not only we have the referred log from the printout of United ACARS record from Ballinger's desk, as provided by Ballinger himself to the 9/11 Commission and eventually released in 2009 [1]. The 9:23 EDT uplink was also addressed by Team 7 during Ed Ballinger's interview on April 14, 2004 in Washington, DC (2). The implications of this message and, in particular, of its format will be fully analyzed in a next post.

The chart of ACARS messages from UAL dispatch

One thing many people ignore, however, is that Ballinger sent a subsequent uplink to United 175 at 9:51 EDT, that is 48 minutes after United 175 had officially crashed in New York and 28 minutes after the previous confirmed ACARS communication to the aircraft sent at 9:23 EDT. This information is contained in an official record apparently released through FOIA in 2009 called "T7 B18 United AL 9-11 ACARS Fdr- Entire Contents- ACARS Messages 569.pdf. This document contains a chart of messages to and from United aircraft from 13:00 to 14:08 UTC, including United 175 and United 93. Unlike the Printout of ARINC logs released on mid December 2011, whose authenticity is far from being unquestionable, this document clearly reports the stamp "WARNING: THIS DOCUMENT CONTAINS SENSITIVE SECURITY INFORMATION" on each of the 66 pages, as required by the Department of Homeland Security, and particularly the Transportation Security Administration, under 2003 CFR Title 49, Volume 8. Also, each page is marked with an unique Bates number (from UASSIl00036029 to UASSIl00036090.04).

p. 5/66 from Chart of ACARS messages from UAL dispatch

The first eye-catching feature of this document is the fact that all downlinks (i.e. air-to-ground messages sent from aircraft to dispatchers) appear as unreadable or hardly readable. For some unspecified reason, these rows were apparently marked with a yellow highlighter or a similar tool in the original paper record, as confirmed by the warning "Notes: Messages from aircraft are shaded" reported on each page. As known, shaded text portions have a very bad rendering once xeroxed or scanned. As a result, the downlink rows in the chart are probably well readable in the original paper version, but in the PDF publicly available they appear as they were "masked out". In some cases, it is possible to read the UTC time, the flight number, the tail number, the targeted dispatcher (EB = Ed Ballinger or CM = Chad McCurdy), the route and at least part of the text message behind the highlighting. In other cases, it is completely impossible to figure out the text behind the dark shade.

Another surprising aspect of this document is the fact that the timeline ends at an abnormal and unusual time such as 14:08 UTC (10:08 EDT). As widely known to many ACARS researchers, seven uplink messages were sent out from UAL dispatchers to United 93 between 14:10 UTC and 14:20 UTC (Messages #18 - 25 in Winter's list) and therefore they are not reported in this document. While there is still a fierce debate as to whether and which of such messages were received by the aircraft, it is an ascertained and unquestionable fact that they were sent. Therefore, we would expect that the timeline would end at least at 14:30 UTC, if not later, so that all messages related to United 93 would be included in the chart. Remarkably, messages to and from other United aircraft of secondary importance were included in this table, but for some unspecified reason the last seven messages to United 93, one of the four aircraft involved in 9/11, were not. Again, we won't speculate here about the reasons of such decision. However, the fact that the timeline ends at an unexpected time such as 14:08 UTC, along with the exclusion of messages to United 93 which are of vital importance for the ACARS research on 9/11, is something that we wouldn't hesitate to define as suspicious.

In spite of all this abnormal redaction and missing data, this document uncovers an information of groundbreaking importance for the purposes of our ACARS research at page 48: at 13:51 UTC (9:51 EDT) Ballinger sent a bunch of uplinks to several United aircraft, including United 93 and - which is more surprising - United 175. The same text message, "LAND ASP AT NEAREST --NEAREST AIRPORT.ASP .ASP ON GROND.ANYWERE", was sent to Flight 8151, 175, 63, 17, 163, 8146, 27, 8155, 81, 93 and 161 (in some cases twice to the same aircraft within the same minute, see p. 48 and 49).

p. 48. Framed in red the uplink sent to United 175 at 13:51 UTC (9:51 EDT)

Ballinger's timeline from September 12, 2001

A conclusive confirmation that Ballinger sent a late uplink to United 175 at 13:51 UTC (9:51 EDT) comes from his own timeline. "T7 B20 Timelines 9-11 2 of 2 Fdr- Ed Ballinger Timeline 243", released in 2009, is a 2 pages document which reports the timeline of the events as compiled by Ed Ballinger on September 12, 2001, the day after the tragic event (the date is reported at the top of the document). The chart includes the main events on the morning of 9/11 according to Ballinger from 13:01 UTC to 14:11 UTC, including uplinks and downlinks to/from both United aircraft involved in the accidents along with other relevant information. Just like the chart of United Airlines ACARS from dispatch shown in the section above, this document is an official record. Along with the stamp "WARNING: THIS DOCUMENT CONTAINS SENSITIVE SECURITY INFORMATION", each page is provided with a unique Bates number (UASS12-00000006 and UASS12-00000007). This timeline confirms that Ballinger sent an uplink at 13:51 UTC and remembered about this detail on the day after 9/11:

Ballinger's timeline of 911 events, p. 1
Ballinger's timeline of 911 events, p. 2
Framed in red the row confirming the uplink sent to United 175 at 13:51 UTC (9:51 EDT)

One more time, we have evidence coming from an official document of unquestionable authenticity. The author (the same dispatcher who had sent the uplink the day before) and the date of the document (September 12, 2001) provide additional evidential authenticity to this record and also corroborate the authenticity of the Chart of UAL ACARS from UAL dispatch we have seen in the section above. Although the ACARS log for this uplink has not yet made public for reasons we won't speculate in this article, both documents reported here corroborate themselves and prove beyond any doubt that Ed Ballinger actually sent an uplink to United 175, 48 minutes after the alleged crash time.

Questions and implications of this new finding

The first obvious question raised by this new evidence is 'why' should Ballinger send such an order ('Land asap at the nearest airport') to the cockpit of United 175 at 9:51 EDT if he did not know from some source that the aircraft was actually still airborne. The supporters of the official story might argue that Ballinger may not be aware at that time that the second aircraft which had crashed in New York was in fact one of the United flights under his control that morning. However, we know from Ballinger's interview to Team 7 in April 2004 that Ballinger was officially informed by Andy Studdert, Chief Operating Officer and Executive Vice President of United Airlines, at 9:24 EDT that United 175 had been involved in an accident in New York:

[U] At 9:19 a.m. Ballinger began sending out the following ACARS message to his airborne flights: "Beware any cockpit intrusion ... Two aircraft in NY hit Trade Center Builds... " This message went to United flight 161 at 9:19 a.m., and to flights 91, 23, 8117, 8179 at 9:20 a.m. and flight 17 at 9:21 a.m.


[U] At 9:23 a.m. Ballinger transmitted his "cockpit intrusion" message (identical to the previous ones) to Flights 27, 175, 81, 8151, 8155, 8179 and 161. With respect to this message to Flight 175, Ballinger indicated that he was aware that two commercial aircraft had hit the World Trade Center and that Flight 175 had been hijacked, but he wasn't sure whether he knew that it had crashed by this point (in which case the message would simply have been caused by his haste to get the word out to all of his flights as soon as possible).

[U] At 9:24 a.m. Ballinger received along with all United Airlines stations the following alert (sent at 9:22 a.m.) in the name of Andy Studdert: "Flt 175-11 BOS/LAX has been involved in an accident at New York. The Crisis Center has been activated. United Airlines policy strictly prohibits giving information or making statements about the incident to the news media or public officials by any employee. WHQPR will release any and all subsequent information."

[U] Simultaneously with receipt of the Studdert message, Ballinger transmitted the same "cockpit intrusion" message to Flights 93, 283, 83, 91, 23, 8179, 8146, 8117 and 17 at 9:24 a.m.

For those who do not know this interview yet, I strongly suggest to read the document in its entirety. The Commission's discomfort in explaining why Ballinger sent a message to United 175 at 9:23 EDT, twenty minutes after the time of the alleged crash in New York, is evident. Note how the Commission remarks that Studdert's communication was sent at 9:22 EDT but received by Ballinger only two minutes later, at 9:24 EDT, a fact which is confirmed however by several sources, among the others the Ballinger's timeline presented above (see the row "1324Z Planning center notified via CHIALL UAL 175 involved in accident in New York (WHQPO)"). It is obvious that the Commission is striving here to present a credible explanation for this uplink, which raises itself a lot of questions. To provide additional 'credibility' to this theory, the Commission also suggests that the 9:23 EDT message was "caused by [Ballinger's] haste to get the word out to all of his flights". Nonetheless, doing so, the Commission also marks 9:24 EDT as the time when Ballinger was officially informed by the airline that United 175 had suffered an accident. This raises the question, among many others we will list below, why did the dispatcher feel the need to send a subsequent uplink to United 175 at 9:51 EDT, 27 minutes after receiving such information. It is not surprising that no reference to this late uplink is made throughout Ballinger's interview to Team 7.

United 175 first "missing", then "found"

The uplink sent at 9:51 EDT offers a possible explanation to another tormenting question: why did Ballinger still consider United 175 as "missing" at around 9:40 EDT and, only one minute later, as "found". We know about this sudden 'change of awareness' from two of his uplinks sent in rapid sequence to United 93 between 9:40 and 9:41 EDT:

.CHIAKUA 111340/ED


;09111341 108575 0638
.CHIAKUA 111341/ED

;09111341 108575 0639

Both messages are also reported in the chart of ACARS messages to/from United aircraft that is being analyzed in this post:

Screenshot from p. 31. Framed in red the uplinks sent by Ballinger to United 93 at 13:40 and 13:41 UTC

Within one minute, Ballinger sent two separate uplinks to United 93 with the same text message, but a different final information: the first message (# 0638) reports "UAL 175/93 MISSING", while the second one (# 0639) shows "UAL 175/93 FOUND". One more time, it is interesting to note how the Commission tries to skirt around the real questions raised by this sudden change of awareness by the dispatcher:

[U] At 9:36 a.m Ballinger was aware of the following ACARS transmission from fellow dispatcher [  ] to Flight 93: "Hows the wx. Can dispatch be of any assistance?" At Ballinger's initiative, he had begun to split his workload with [    ] at some point prior to this.

[U]At that point, Ballinger's ACARS message was again changed with the addition of "UAL 175-93 - missing" at the end. This communication went out at 9:36 a.m. to Flights 8155 and 83; at 9:37 a.m. to Flights 283, 163, and 81; and at 9:41 a.m. to Flight 93. Finally, at 9:41 a.m. Ballinger sent the previous message to Flight 93 again with the addition at the end of "UAL 175/93 found."

No real explanation is provided as to why Ballinger first considered United 175 and United 93 as "missing" (9:40  EDT) and immediately after as "found" (9:41 EDT). If we believe to the Commission, Ballinger had been already officially informed at 9:24 EDT by the UAL Chief Operating Officer about the accident occurred to United 175, as we have seen above. So why was he still looking for United 175 sixteen minutes later, at 9:40 EDT, and considered the aircraft as "missing"? And which information did he receive immediately after that led him to consider United 175 as "found" along with United 93?

Unfortunately no conclusive answers can be given to the above questions. It is clear, however, that something does not add up in the official timeline reconstruction, as provided by the Commission in this interview to Ballinger. We don't know nor we will try to speculate as to the possible source of Ballinger, however the most probable and logical conclusion is that the dispatcher received some information between 9:40 and 9:41 EDT that suggested him that United 175 had in fact not crashed and was not lost as reported by Andy Studdert and by the media.

Other reports appear to be consistent with our claim. For example, the document MFR 04017175 is the minutes from the interview by Team 7 and 8 to the United Airlines System Operations Control (SOC) Center and Crisis Center members on November 20, 2003 at the United Airlines SOC, Chicago, IL. Parts of this document are of extreme importance for our analysis and are reported below:

[U] When asked about the technical capabilities of the ASD (airspace situational display) program used by the dispatchers on their monitors to track planes, all United representatives conferred that the program's display refreshes every 60 seconds. If a plane was "squawking" a different code, the United representatives did not believe that would change the appearance of the track on the ASD. For instance, UAL 93, which was out of communication for a longer time than UAL 175, appeared to be "coasting" once the transponder was turned off. Barber did not think at the time that modifying the transponder code would be apparent to dispatchers through the use of ASD. 

[U] McCurdy recollected that at the time of the crash into tower 2, the display on Ballenger's monitor still showed UAL 175 at 31,000 ft, having just deviated from the normal flight plan and heading into a big tum back east. The track on Ballenger's ASD was frozen long after it was known the plane had crashed into tower 2.

[U] Rubie Green interjected that the program was designed to maintain a tag on a flight as it moved across the map from center to center. Various code changes would not affect the track as it appeared to the dispatcher. McCurdy said that the ASD provides a rough track of a plane's progress; minute alterations in the flight plan wouldn't be reflected on the dispatchers display because such details only mattered to the pilot and the air traffic controller. "The purpose of the track is to keep the plane out of the path of a thunderstorm," McCurdy said.

[U] When they saw the second plane go in on CNN, instinctively Barber thought it was UAL 175, but they did not a positive identification right away. Because the scene caused much disturbance on the dispatch floor, Barber told the staff to stay at their desks and focus on their jobs. Barber noted that his log stated that at 8:20 a.m. (CT) UAL 175 was confirmed.

The last sentence in bold is pretty obscure, but extremely significant. The impression is that some information after the word "confirmed" was truncated or the sentence was intentionally left cryptic. Taking into a account that the location is United Airlines’ System Operations Control (SOC) center just outside Chicago, however, the reference to "his log" is a clear indication to Barber's ACARS log, which leads to conclude that at 8:20 Central Time (9:20 EDT) United 175 still appeared to be a "confirmed" aircraft according to the ACARS record and therefore could not be the same aircraft that every one at the SOC center had seen crashing against the South Tower on TV during the live CNN coverage. The entire sentence is of vital importance to understand the situation at the United SOC center around 9:20 EDT and may shed light to the subsequent behavior by Ballinger. Barber suggests that, when he saw the second plane hitting the tower in New York on TV, he instinctively suspected it could be United 175 because that flight had been already reported as hijacked and off-course, however this information was not confirmed by the ACARS log nor by the ASD monitor. If our interpretation is correct, then this is an additional evidence that no failure log had been yet reported by ARINC to the originator (UAL dispatch) 17 minutes after the alleged impact. This fact is pretty surprising if we consider that Ballinger had sent his first uplink to United 175 at 9:03 EDT ("How is the ride. Anything dispatch can do for you") soon after being informed of the possible hijack and only instants after Sandy Rogers had sent another uplink at the same time ("NY aproach lookin for ya on 127.4"). According to MFR 04017215, "Rogers-initiated message [was] not received by the aircraft". If this were true, then a failure report should have been sent to the UAL dispatch and Barber would have not seen United 175 as "confirmed" at 9:20 EDT. Both information are mutually exclusive. If an aircraft crashes, it just stops sending tracking messages to the ARINC CPS. The CPS keeps on searching for the aircraft for a maximum of 11 minutes, then generates a Reason Code 231 and sends a failure report back to the originator. But this is in conflict with an aircraft "confirmed". The most probable explanation for this discrepancy is that the information contained in MFR 04017215 is false (and remains unsubstantiated in any case). Both Rogers' and Ballinger's uplinks at 9:03 EDT were in fact received by the aircraft and this explains why Barber still saw the aircraft as confirmed in his own logs and also explains why the subsequent uplink sent by Ballinger at 9:23 EDT, as reported in the printout of his personal logs, shows two timestamps and has not the same format as the last message sent to United 93 at 10:21 EDT:


;09111323 108575 0574

To make a long story short: such format requires either one of the following conditions: United 175 was airborne or had crashed less than 11 minutes before. Since the crash had allegedly occurred 20 minutes before, only the first condition applies here.

United 175 "was not acting appropriately"

Michael Ruppert dedicated a section of his book Crossing the Rubicon to Ed Ballinger. Parts of this section are relevant for our analysis and are reported below:

Suburban Flight Dispatcher to Recount Worst Day

Today, Ed Ballinger will speak to a roomful of strangers about the one subject he doesn’t care to discuss: The first two hours of his shift as a flight dispatcher for United Airlines on the morning of September 11, 2001.
The Arlington Heights resident and former United Airlines employee will meet with a sub-committee of the 9/11 commission in Washington, DC, so panel members can decide whether his testimony warrants his appearance before the full commission.
Ballinger is there because he was in charge of United Flights 175 and 93 when they crashed into the World Trade Center and a field near Shanksville, PA.

Because perhaps, just perhaps, offering his story will calm the whispering thought that troubles him still: If he’d been told the full extent of what was unfolding sooner that morning, he might have saved Flight 93.
“I don’t know what [the panel appearance] is going to be,” he said Tuesday after arriving in the capital. “They want to know what I did and why. I’ve been told it’s not finger pointing. It’s just finding out what happened.”

“When September 11 came along, that morning, I had 16 flights taking off from the East Coast of the US to the West Coast,” he said. “When I sat down, these 16 flights were taking off or just getting ready to take off.”
Ballinger contacted all his flights to warn them. But United Flight 175 “was not acting appropriately.”
He asked Flight 175 to respond. The pilot didn’t reply and Ballinger was forced to conclude he’d been compromised and that he was rogue.

[This is exactly what long-standing FAA procedure told him to assume. See Chapter 17.]
By now, the situation was terribly different from previous hijackings Ballinger had handled. In two hours, he sent 122 messages.
“I was like screaming on the keyboard. I think I talked to two flights visually. The rest was all banging out short messages,” he said.

Ballinger said he was never the same after September 11, and was reluctant to return to work.
“That first day, I’m lucky I didn’t hit anyone,” he said. “I drove through every red light getting home as quickly as possible. I wanted to get home and medicate myself.”
At work, he started second-guessing his own decisions and became, in his words, “ultra-ultra conservative.”
“I came to a point where nothing was safe enough,” he recalled. “[I] couldn’t even make a decision. It put you in jeopardy in every respect.”
At age 63, he was told to take a medical leave and long-term disability. He said he couldn’t do that. He was then asked if he could retire in six hours. A Social Security Administration psychiatrist put him on total disability.

"[United 175] was not acting appropriately" is a statement that may sound perfectly plausible to someone who never studied ACARS, especially if referred to an aircraft that has been hijacked and is off-course. For those who have knowledge about how ACARS communications between airline and aircraft work and about the timeline of the events, however, Ballinger's words sound sibylline at the very least. 

To the benefit of those who are less familiar with ACARS, it should be reminded here that all messages sent by the airline to an aircraft (uplinks) are considered as delivered as long as no failure log is reported back to the originator (dispatcher). In other words, the lack of any failure report is considered itself by the dispatcher as a confirmation that an uplink has been successfully delivered. Otherwise, whenever an aircraft fails to automatically acknowledge a message for any reason (including, of course, the case of a fatal accident), the ARINC CPS generates an error code and sends a failure report back to the dispatcher's printer and/or screen within some minutes. In this way, the dispatcher is notified that there is some problem with his aircraft and can take the appropriate steps to contact the aircraft through different channels. If United 175 had actually crashed at 9:03 EDT in New York, then Ballinger should not be surprised that the cockpit was not replying to his uplinks or sending any other manual downlinks. Given the circumstances, this would be an expected behavior. Instead, Ballinger was possibly surprised that neither he nor any other dispatcher at United Airlines SOC center in Chicago had received any failure report from the ARINC CPS yet for two uplinks sent at 9:03 EDT and for one subsequent uplink sent at 9:23 EDT to United 175, as the statement by Mike Barber quoted above also suggests. While the available documentation does not allow us to conclusively prove this assertion, everything points consistently into the same direction. Ballinger was being told by the TV and by the United management that his aircraft had crashed, but his ACARS log and his ASD were not confirming that, therefore he desperately kept on trying to contact his aircraft until 9:51 EDT. As a very experienced dispatcher, Ballinger knew that, if his aircraft had really crashed, this would reflect in his ACARS log with one or more appropriate failure reports for any unsuccessfully delivered uplink. As we have seen in both messages sent to United 93 between 9:40 EDT and 9:41 EDT, at that time Ballinger knew that two aircraft had suffered a fatal accident in New York, still he was not entirely convinced that one of them was actually United 175, as reported officially. If he were, then he would not consider United 175 first as "missing" and later as "found" at around 9:40 EDT and in no circumstances would he contact the aircraft again at 9:51 EDT. At the current state of the research, this appears to be the only plausible explanation for his otherwise sudden behavior and the only plausible explanation why, years after, he stated that United 175 "was not acting appropriately" as reported by Michael Ruppert.


For most, if not all the questions raised by this article no conclusive evidence can still be presented after almost 11 years. Several official records are still classified, other have been apparently declassified but are of dubious authenticity or have been surprisingly released with shaded
information. Finding the "truth" within this tangle of omissions, conflicting reports, missing logs, different "FLoc" numbers etc. is beyond us. While we won't speculate here about the possible reasons for such omissions and discrepancies, it is an unquestionable fact that Ed Ballinger sent an uplink to United 175 at 9:51 EDT. The evidence comes from two official declassified records whose authenticity is beyond any doubt. Our only goal here is to present facts and raise questions which are still unanswered:

  • if United 175 had crashed at 9:03 EDT against the South Tower, then why did the aircraft still appear as "confirmed" in Barber's log at 9:20 EDT? 
  • why does the log for the uplink sent by Ballinger to United 175 at 9:23 EDT show two timestamps although 20 minutes had already elapsed since the time of the alleged crash? After twenty minutes from the crash, we would expect that the ARINC CPS would react with a Reason Code 231 (see for example the first ICPUL block for American 77 at 10:00 EDT, 22 minutes after the alleged crash against the Pentagon), what would result in turn in a failure report on Ballinger's printer/screen and a log with one only timestamp, such as the last message sent to United 93 at 10:21 EDT. What does such discrepancy suggest?
  • how could possibly Ballinger send an uplink to United 93 at 9:40 ending with "United 175/93 missing" and one minute later another message to United 93 ending with "United 175/93 found" if he had not received in the meanwhile (from some unidentified source) information suggesting that United 175 was in fact still airborne? 
  • why did Ballinger send another uplink to United 175 at 9:51 EDT, 48 minutes after the alleged crash, 28 minutes after sending the previous uplink (which apparently had not yet produced any failure report) and 27 minutes after being officially notified about the crash by Andy Studdert? Why should he urge an aircraft already declared as 'crashed' to land at the nearest airport?
  • and finally, what did Ballinger actually mean with "[United 175] was not acting appropriately"? How could a dispatcher with 44 years of professional career possibly overlook a failure report and keep on trying to contact his aircraft for almost one hour after the alleged crash time if he hadn't some information that led him to conclude that the aircraft was in fact not "lost"? The whole UAL dispatch in Chicago was focused on both United aircraft considered as hijacked. How could possibly all of them miss a failure report in their logs?

The supporters of the official story may argue again that the decision of sending a late uplink to United 175 may be simply the result of Ballinger's haste to get the word out or the result of the conflicting information he was receiving on the morning of 9/11. While this is possible in theory, then the question arises why did the Commission not bother to address this specific log during Ballinger's interview on April 14, 2004. Why is this log missing in the UAL record of Ballinger's logs released in 2009 under FOIA? Why are several pages from that document missing? Why are the logs for United 175 completely missing in the so called "Printout of ARINC logs" made public in December 2011?

The answers to the above questions will probably shed light one day to what really happened to United 175. Understanding what really happened to United 175 is the key to understand what really happened on 9/11.

Wednesday, February 15, 2012

Ballinger's printout in .CSV format

Posted by bambooboy

This article is to announce the release of the Ballinger's ACARS Printout in .csv format. I merely hand copied the data from the original .pdf file Team7/Box13 - FBI 302s ACARS into an OpenOffice spreadsheet, then saved it with a .CSV extension. From that, I also produced a tabular version of the same data to make things easier for 9/11 researchers. As a result, two files were created.

In the first one, Ballinger_TEXTUAL_CSV.csv, I simply created a text version from the scanned version. In the second one, Ballinger_LINEAR_CSV.csv, I have reorganized the same data in a linear format to visually help the reader spotting similarities and differences between the various messages.

In the "Ballinger_LINEAR_CSV.csv" file, I have added 3 columns at the beginning of each data row: the first 2 are related to "scan" and "time" messages order. The third is for quick reference to "uplink/downlink direction" of communication. I didn't add any heading for data fields (except those for "neutral voices" such as Flag_01, Flag_02, and so on), because some are still under debate.

Note. The linear comparison allows to highlight some new interesting points, especially the values shown under the column "flag_31". This column shows that the messages uplinked to United 93 are marked by a value in front of the aircraft flight number [UA93], whereas such value can be [1], [2] or blank [ ] (example. 1UA93).

These are other interesting points:
  • messages with a "blank" [ ] value (time ordered list "2" 13:22; "11" 13:50; "12" 13:50; "13" 13:51; "14" 13:51) are all transmitted in "AGM mode" (to the printer). Note: The downlink (time ordered message: "1" 13:21) is also transmitted in "AGM mode"
  • the value "1" values appear for all the uplinks sent in "CMD mode" (to the cockpit screen)
  • the value "1" value appears to be related to messages positively received by UA93 (such as message time ordered "3" at 13:23 UTC)
  • the value "2" value only appears once and is associated to the only message which was certainly received/undelivered( time ordered "18" 14:20 UTC). This uplink (#24 in Winter's list)is a CMD message (to the cockpit's screen).
  • the uplink ordered as "18" was sent by "ROB" (ROBERT BRITTAIN), and contains RGS the indication "/GL DEC"

Finally, I made a cross-reference to the data from the ARINC logs. The results are shown in the table below:

FLoc BEPts Target Stn Stn Org TimeStamp Reason Code Block Type /GL
365464105 20010911 14:13:30


365550345 20010911 14:13:40


365612804 20010911 14:13:50


365678382 20010911 14:14:00

365678701 20010911 14:14:00

367059755 20010911 14:17:39

20010911 14:17:00

367059889 20010911 14:17:39

367187539 20010911 14:18:03

20010911 14:17:00

367187673 20010911 14:18:03

367542701 20010911 14:19:04

20010911 14:19:00

367542835 20010911 14:19:04

368197741 20010911 14:21:06

20010911 14:20:00

368197875 20010911 14:21:06


UAL communication marked as "TIME_ORDER_18" in my list above, which matches Message #24 in Winter's list and the ULMSG block "FLoc 368197741... BEPts 20010911 14:21:06 ICPUL... Reason Code 231" in the ARINC logs shows "/GL DEC" as target station and "ROB" (Robert Brittain) as dispatcher. If we look at column "Flag_31", we notice that this is the only message reporting the value "2".
Unfortunately we have no clear indication from the ARINC specifications or any other official document what these values ("blank","1" and "2") are referred to. Therefore, we can only speculate trying to draw logical conclusions based on the available data:

  • Ballinger's printout, as printed at his UAL workstation, reflect the data as returned by ARINC to UAL after an uplink is sent [1]
  • Only one message from Ballinger's printout is surely unreceived/undelivered: this is the last message (marked as "TIME_ORDER_18" in my list and referred as Message #24 by Winter) and this shows the value "2", which is not a direct function of "CMD" or "AGM"
  • In the ARINC logs for United 93 there are five ICPUL blocks with Reason Code 231 ("No Station To")
  • Both in ARINC logs and in Ballinger's printout there are three ULMSG blocks showing "GL/CMI" as target RGS
  • Both in ARINC logs and in Ballinger's printout there is only one ULMSG block showing "GL/DEC" as target RGS
  • The last three ULMSG blocks showing "GL/CMI" as target station in the ARINC logs are also apparently followed by an ICPUL block with Reason Code 231 (see above)
  • The corresponding three messages in Ballinger's printout with target station "GL/CMI", however, show "1" as value, as shown in the column "FLAG_31" above
  • In the ARINC logs the last ULMSG block also shows "GL/DEC" as RGS and is also followed by an ICPUL block with Reason Code 231

[1] This appears clear from last uplink (asterisks, no second timestamp, no counter number)  and from the statement by Steve Ledger, Director of AQP services, in MFR04020032:

MFR 04020032, p. 2

Original post (in Italian) here.

Sunday, January 29, 2012

VHF propagation from aircraft at 130 MHz

Posted by: Dennis Cimino

First, I want to state for the record that I have been working with high power R.F. transmitters and countermeasures sets, radar, communications, deception repeaters and jammers since 1973, and am quite experienced with in-flight dynamics of VHF signal propagation from both low altitude and high altitude aircraft, both civilian and military. Now, the average person is not too familiar with voltage standing wave ratios, or effective radiated power, insertion or line losses, reflected power, antenna gain factors or for that matter antenna radiation patterns on aircraft, as I am. I have extensive experience in these matters and have the actual aviation experience in a wide variety of aircraft, with regard to everything from H.F. long haul communications to millimeter wave jamming or ECM systems, radar, and navigation equipment. For this discussion we are going to talk strictly about 130 MHz, not 2 MHz, not 17 GHz, and the beam pattern and directionality and effective ranges of these systems on both commercial, military and commercial aircraft both below and above the 12,500 pound weight category.

For those of you who are unfamiliar with path loss nomographs for 130 MHz, I would like you to make it a point to study the diagram below. Notice that no assumption is made for effective radiated power, or system gain factors, and there is a reason for this.

Click on the image to enlarge
This diagram is shown to illustrate the fact that, contrary to assertions by JREF and Unexplained Mysteries bloggers, radio waves do not just "keep on propagating" outwards at their original radiated power levels, without being attenuated over distance. When the path losses and other factors exceed the transmitter power and effective radiated power, as well as minimum discernible signal sensitivity of the receiver system, on any radial from the aircraft, and any angle of incidence, there is no possible communication then. Does this mean that the signals just stop moving thru space? Absolutely not. But what this does mean is that as the distance increases to a point whereupon the signal power level decays below any possibility of detection by even triple conversion receivers with very selective front end circuitry that have incredibly high (-148 dBm or thereabouts) minimum discernible signal capture capability (which ACARS does not, nominally have, at it’s fairly robust –107 dBm), then beyond that range, detection and demodulation by any terrestrial, high gain, very directional and perhaps non interferometry based receive system, is highly unlikely to happen. In any case, radio signals do not keep on radiating outwards without attenuation occurring due to signal density issues resultant from the fact that the greater distance from a transmitter from any antenna, the power distribution in fixed space, by laws of physics, will diminish with distance. Due to the totally unpredictable nature of the antenna radiation patterns of VHF blade antennae used by ACARS, it is a false assertion to state that there are no limitations between the RGS stations and the aircraft transmitter antenna for COM3, usually used on most Boeing airplanes, circa 1980’s and onwards, for ACARS.
In any case, what I would like to start with is that the aircraft and the antenna jointly form the transmit and receive radiation pattern in ways that are radically different from these same antenna systems being mounted on flat ground planes that offer at the very least a 90 degree counterpoise to the plane wave or electrical field leaving the antenna. The reason I cite this is that for any isotropic or non-directional antenna system, which these are not, due to their shapes being swept to minimize aerodynamic drag factors and prevent ice pickup or vibration resonances, these antennae used on commercial and military aircraft for VHF COMMUNICATIONS are what are referred to as ‘blade’ antennae of the type used on most commercial aircraft, including B-757/B-767’s.

For such antennae, there are some considerations that apply to them due to their shorter than quarter wave physical radiating length offset from the aircraft’s very curved fuselage or empennage. This results in significantly higher V.S.W.R. or ‘reflected’ energy back to the transmitter and not into free space. In addition to this, the shorter physical radiating element length versus the curved fuselage will radically change the radiation pattern and add directivity to these antennae, typically along the fuselage plane, fore and aft, as well as pushing the radiation pattern upwards or away (assuming the antenna is top mounted) so that the beam shape is not cardioid in nature but scalloped and with significant major pattern lobes that tend to create significant null zones that effectively reduce radiated power in those areas to the sides or in the ‘X’ plane (horizontal) by several ‘dB’ of gain, while significantly favoring the fore and aft orientation along the fuselage. In the ‘Y’ axis (Vertical), looking at the beam pattern, the field lobes from the antenna depart the skin of the aircraft and contour upwards, once again, assuming the antenna is top mounted, and conversely, ‘downwards’ if the antenna is belly mounted. To characterize the full radiation or beam pattern, it would appear heavily scalloped in the ‘X’ axis, and quite finger or balloon lobed in the ‘Y’ axis, (vertical) plane. In effect, the antenna that was supposed to be fairly omni-directional now is quite directional both fore and aft and has markedly higher gain factors in those directions, as well as pushing the pattern upwards into free space at any number of angles less than 90 degrees off the horizontal. The resultant 3-dimensional plot begins to look like a twisted doggie balloon shape and no longer resembles a spherical omni-directional beam plot.

The reason I mention this is that this directivity is nothing that can be readily compensated for without exotic counterpoise shapes around the base of the antenna, or multiple ‘Yagi’ type of elements in other directions to flatten or change the beam pattern. To compensate for these exotic and quite scalloped and lobed patterns that become reality when these relatively inefficient due to shorter radiating element length antennae are joined to a curving cylindrical tube which airplane fuselages tend to be, relative to the radiated field. And I would like to state that though there is a great deal of reciprocity between TRANSMIT and RECEIVE patterns, they do not necessarily fully reciprocate or remain the same for both functions due to any number of factors we will not discuss herein.

In any case, what I have just described is the highly irregular and moderately unpredictable and undesirable directivity of an otherwise fairly omni-directional antenna system. It is important to note this because a 3 dBm power differential in any of these planes, radiation pattern wise, effectively is a half power addition or reduction, with significant null points deeper than this that occur quite naturally, rendering the pattern even more complex and difficult to factor using system loss calculations, without actually making measurements in every axis with the aircraft either raised up and outside of what is called ‘near field’ distances of the ground below the aircraft. Simply put, real world antenna radiation pattern measurements are possible and actually done, but in most cases scaled models with scaled frequencies, are typically used on non full-sized models inside of anechoic chambers or OTS (outdoor test) areas. By large, most aircraft manufacturers do not attempt to make these measurements but make assumptions about radiation patterns that are not necessarily founded in known factual testing data, as usually is derived by MILITARY aircraft certifications laboratories who have a much more vested interest in characterizing these radiation patterns to maximize system effectiveness and head off or prevent unwanted ‘dead zones’ around the fighter or bomber or jamming platform these antennae are mounted on. On many tactical jamming aircraft, the blade antenna arrays are more or less in ‘Yagi’ configurations to give directional gain that the mission capability of the aircraft needs to make maximum effective use of a communications jammer mounted on the aircraft. This is, however, never done on commercial airliner or Part 23 aircraft, to minimize cost and reduce weight.

As we have now more or less just barely touched on the radiation pattern, we have not yet begun to talk about signal polarization issues, and why they go hand in hand with more fully understanding how a theoretical two-way path loss calculation and predicted range of a system can be quite off in comparison to real world or ‘true’ and valid path losses and system effective radiated power determination, or receive sensitivity calculations.

What I am getting here is that a perfect isotropic vertical radiator element that rises 90 degrees off of a ground plane, or is oriented in the pure ‘Y’ axis pointed straight up, effectively has a VERTICAL ELECTRICAL FIELD POLARIZATION OF THE SIGNAL. In lay-person’s terms, ‘polarity’ of the electrical field, ideally, should be the same on both the transmit and receive end, to maximize signal transfer. In real life, this is difficult to achieve with swept blade antennae and curving aircraft fuselages which are the ground plane or ‘counterpoise’ for the antenna itself. The resultant polarization skewing hence causes a coupling factor inefficiency to occur, relative to the very polarization fixed antenna on the ground, intended to receive these signals.
IF the electrical field polarization shifts fully 90 degrees so it is not vertical at all but more ‘horizontal’ in relation to the very VERTICAL ground antennae respective polarity, the coupling mismatch is now at the very least ‘6’ dB less than optimal, of not more due to the curving fuselage, which is not a flat ground plane at all. Every ‘3’ dB is a half power loss when that number is a negative change. Why is this important?

Let’s theorize that from the transmitter rack, of the 50 watts transmitted off the jack in the rack itself, after ‘xx’ dB of loss in the transmission line, which in some cases is several meters in length, we are not going to see 50 watts of R.F. energy radiated into free space off of this antenna. Instead, if we are lucky, we’re more likely to see far less than 20 watts or thereabouts, leaving in all directions, not just going out in a single plane wave directly at the receive system on the ground, miles below. To better visualize this, imagine a light bulb on a lamp without a shade radiating light energy in all directions more or less evenly. Though light energy is significantly higher in frequency than is 130 Mhz. ACARS data link signal data, imagine the light bulb now has an array of fiber optics tubes radiating in all directions, affixed to the light bulb. In effect, the result is not anywhere near an omni-directional pattern at all, but a highly irregular, porcupine spoked shaped pattern of peaks and nulls radiating outwards, resulting in shadows in all directions on the walls of the room, and bright spots. This is more or less what the irregular radiation pattern of the ACARS blade antenna would look like if this were optical energy at a higher frequency. This analogy, as coarse as it may seem, is more or less descriptive of R.F. power density variations from a very spiked and valley ridden pattern radiating off the fuselage from the ACARS blade antenna, typically mounted on the aft belly of the fuselage on some Boeing aircraft, such as is the case with the B-737NG.

Why is this important to understand, relative to the ACARS two-way range issue? Well, simply put, the moderately less than optimal V.S.W.R. of the antenna and transmission line and airplane fuselage now has reflected or ‘lost’ significant amounts of outbound R.F. energy that would have gone into free space in any number of ‘X’ and ‘Y’ and in fact, ‘Z’ plane directions from the radiating antenna or ‘blade’ on the fuselage. So we’re not dealing with our original 50 watts any longer, we are now pushing less than half of that into the free space around the airplane, in virtually all directions, in a very far from omni-directional radiation pattern, with deep peaks and nulls radiating outwards in all directions but overall favoring the fore and aft longitudinal axis of the aircraft. Translated, it means the myriad of ground stations around the aircraft will not be seeing anything close to the optimal range nomograph numbers at all, based on free space losses, as well as the very irregular antenna radiation pattern of the aircraft’s VHF blade antennas that are used by ACARS.

So now we are going to bring up the 200 mile claimed range number here. And the reason why, is that yes, in theory, due to the minimum discernible signal or sensitivity level of the ACARS receiver system of both the plane and the ground station is more or less known or can be approximated, what cannot be known is the coupling factor perturbations due to beam shaping and irregular radiation patterns that occur when blade antennas used in VHF communications are mounted on tubular aircraft fuselages. This results in significantly ‘lower’ than the expected or theoretical best 200 mile range supposition, by as much as 80 percent in real life.

Any experienced aviator who has used VOR navigation and who understands how the F.A.A. determined SERVICE VOLUME models for the each class of VOR facility, knows that even at FL-450, and above, a realm that few airliners routinely will fly at, by the way, due to cabin pressurization issues and aerodynamics, the effective range of the slightly lower in frequency of 108 to 118 Mhz., is reduced from that altitude to FL-600 or sixty thousand feet. Why is this? Well, ground obstructions, and earth curvature now come into play here, as well as other similar signal degrading changes, and therefore the F.A.A.’s own data available to look at for these VOR facilities is less above FL-450. The F.A.A. didn’t arbitrarily pick these numbers out of some hat somewhere. They were derived by in-flight testing over literally all terrain types and at all altitudes, inclusive of FL-600 in some cases. The service volume diagrams from the F.A.A. website are relatively transferable to ACARS due to similarity of known and demonstrated effective ranges derived thru years of collective experience testing VOR reception service volumes, as well as R.C.O (remote communications outlet) communications ranges.

So we have more or less touched on irregular and highly unpredictable antenna radiation patterns in both the transmit and receive capability of 130 Mhz. communications and navigation systems in use today, and for all practical purposes really destroyed the rather inconsistent with real world performance, claims of ACARS working out to 200 nautical miles from any RGS station, due to these factors. In real life, no experienced line pilot could ever with a straight face claim that he’s tracked VOR’s at 200 nautical miles without flag tripping and sporadic reception, but also, it would be quite a stretch of the imagination to expect the performance for ACARS to routinely, every time, ever truly meet the outrageous claims of functionality at 200 miles from any aircraft, due to these factors cited here. Power output is not the determining factor here. Earth curvature is the predominant range limiter, as is terrain irregularity and obstructions around the ground station inside both ‘near field’ and ‘far field’ distances from the RGS stations.

As a commercially rated pilot with experience flying at virtually all of these altitudes up thru at least FL-350 in civil and military aircraft both as pilot and test engineer, I have to stipulate here that it is both ‘laughable’ and quite ‘uncommon’ to expect VOR reception much beyond 135 nautical miles even at the higher altitude regimes, and for that matter, to expect ACARS to work much further than these ranges over hilly and irregular terrain with mountains and ridges everywhere to throw a major ‘curve’ into any range calculation for these ACARS path losses.

Unfortunately many people who are claiming expertise in these areas are neither qualified to make these judgments due to a lack of R.F. engineering experience or real world testing experience and backgrounds, nor do they have any real world aircraft flight testing experience or flight experience using these systems in the real world. To assert that ACARS can communicate at 200 miles is not factual nor is it realistic. And it is wholly unfounded by any known factual testing data or practical experience of these outrageously optimistic ranges. Furthermore, I’ll even go one step further here. If ANY experienced and non-anonymous airman with a valid pilot certificate at COMMERCIAL level and decades and thousands of hours of flight experience can validate VOR receptions beyond 150 miles under any circumstances, I would like to see their data and where this took place, in which aircraft, at what altitude. I do not expect many challenges to this more or less hard and fast rule here for VHF being pretty line-of-sight limited with very little effective terrain contouring or tropospheric ducting taking place. Any reasonably experienced line captain who has extensive ACARS experience in the Positive Controlled Airspace is welcome to controvert these claims with hard factual data.

In summary, the radiation patterns of real VHF communications blade antennas on heavy transport category aircraft, are both complex and highly unpredictable except to state that nominally there is some beam pattern lobing that prefers the longitudinal axis of the aircraft, to the fore and aft directions, while also shifting the electrical field far from optimal vertical polarization into any number of less optimal, and very inefficient signal polarizations that result in reduced ranges in most directions, and predictable and even more complex changes when these aircraft roll and bank in turns, further altering their radiation and reception patterns significantly from straight and level flight. Furthermore, as the aircraft’s crew is quite unaware this is in fact occurring, no action can be taken by either the crew of the aircraft’s system that can compensate for this. It is out of their hands entirely.

For the most part, it is unclear why some would surmise that ACARS should always be able to realistically and effectively work out to 200 nautical miles, and furthermore, that stations significantly closer to the aircraft would be totally unseen and not communicating under any circumstances, given what has been discussed here. Yes, the radiation pattern is lobed in all ‘3’ axis off of the aircraft, and yes this means the signal will follow the ground plane of the fuselage and wing structures somewhat, but to make the assertion that a station more than 100 nautical miles away would be favored over one that is less than 20 miles away, is not genuine nor credible.

We did not discuss a whole slew of other factors that adversely impact the effective ranges, such are atmospheric noise sources, co-channel interference, and things such as multi-path and reflections from both near the RGS station as well as the aircraft’s structures itself. Even something such as flap extension or landing gear deployment will significantly change the radiation patterns of most aircraft, whether the aircraft design or ARINC radio engineers like that or not.

ACARS is not likely to work much further than 150 miles in most cases, under any and all circumstances, due to very extensive and recognized use of VOR changeover points on LOW ALTITUDE enroute IFR charts, showing that even at low altitudes up to and inclusive of FL-180, various enroute or Victor Airway reception ranges have been know for years and are published in both U.S. Government and Jeppesen/Sanderson IFR enroute charts and terminal charts for very very good reasons. These changeover points are the very best illustration of actual line-of-sight VHF communications ranges being adversely impacted by hilly terrain and other issues much more so than altitude, because if altitude above the ground were the sole arbiter of this, all changeover points for these low altitude airways or Victor Airways would be the same every single time, but they are not.

They are individual as hairs on your head. And so are the radial distances and ranges from any ACARS ground station using VHF line-of-sight frequencies. By necessity the technical assessment offered here is significantly less technical for a reason. You don’t need to be a pilot or a radio engineer to grasp most of these concepts explained within this moderately brief attempt to illustrate the point that several things are always going to be in play with radio ranges. Those are, to sum them up:

  1. Radio signal strength decay over distance due to atmospheric attenuation and power density diminishment due to radial distances that dictate that with ‘X’ watts of energy radiated outwards from any radio source, that the power density window decreases on any given point far from the origin, even with highly directional and focused beams of radio energy. 

  2. Aircraft radiation patterns are not by their nature remotely close to omni-directional at all, even in the best cases such are transponder antennae at 1030 and 1090 Mhz, perhaps one of the shorter stub blades in use on any airplane, requiring far less ground plane uniformity to properly form an omni-directional radiation pattern.

  3. Curvature of the earth and ground obstructions and line-of-sight VHF propagation characteristics are also significant range limiters at 130 MHz.

  4. RGS stations an order of magnitude CLOSER to distant ones are far more likely to be the best LINE OF SIGHT paths under any and all but the most unusual cases where a mountain or a building between the RGS and the plane may in fact really make a much bigger attenuation factor between a closer station perhaps and a more distant one with a very clean, very direct, non-obstructed path, e.g.: if the more distant station is 100 or more miles away, it’s a real fantasy to state that one a mere 7 to 10 miles away, almost directly under the plane itself, would not be the preferred station, based on path losses alone, and virtually zero earth curvature to deal with there.

And added here as a side note.

The one thing that most lay-persons do not experience in real flight regimes is loss of both communications signals and navigation signals, with something as simple as a small heading change. Something that typically is not a factor on most civilian air carrier aircraft but has been a major problem with general aviation airplanes, is antenna position due to other structures like landing gear, exhaust systems, and other small protuberances on the airplane that really skew the signal so much that it necessitates the pilot change course or heading to blindly fish around and find a better angle offset to allow both ATC to hear you, or for your transponder's signal to be seen by a distant radar station, because your exhaust system or landing gear (in some cases always down because it is not retractable) gets in the way and changes things.

High altitude planes don't typically drop gear and flaps, but they do have many other shape perturbations in both the near field and the far field regions of these antennae that make it unlikely that the aircrew is going to alter course or turn to better line up an antenna pattern 'lobe' so the ground can now see their signal and communicate.

After years of flying both fixed gear and retractable gear planes with all sorts of shapes, I have found that antenna radiation patterns are very very spooky and variable and are not published in any flight manual. But any pilot who knows about near field and far field interference and blocking of his signal would, like me, change course to try to get the signal reception needed for a little bit longer at the extreme outer effective ranges of radar, transponder, and communications / navigation equipment. Airline crews don't do this. But over three decades of flying, I have done it routinely to regain IFF to RADAR functionality, or DME functionality, and for that matter, even COMM/NAV functionality. In one case due to the location of a pair of GPS antennae on the skin of a plane, even GPS was affected somewhat, and it changed RAIM factor on approaches...due to the ground based WAAS augmentation being less optimal on some IFR approaches.

In any case if I find a good VHF radiation pattern plot to ship, I'll send it. But these patterns are very complex. Very very complex, and in real life, as airplane makers don't get real data about this, very highly unpredictable and way less than optimal per engineering calculations for them.

Dennis Cimino
  • Electrical Engineer
  • Commercial Pilot Rating, since 1981 , IFR, MEL ratings since 1980. 
  • Navy Combat Systems Specialist: RADAR, ECM, cryptographic communications   Navy EMI troubleshooter for COMNAVSURFPAC via MOTU-5, San Diego, CA., and under NAVELEX contract.  AN/SLQ-32(V)3 Countermeasures System support specialist.
  • Flight Data Recorder Engineer Smiths Aerospace (Now G.E. Aero)
  • BA-609, IDARS, Military and Commercial
  • Millimeter wave RADAR and countermeasures expert since 1973
  • Two patents held for high powered modulator Triton HP, C-Band, 250kw LONG RANGE Doppler RADAR ( Kavouras ):
  • long pulsewidth RADAR droop compensation network that improved radar output power thru long pulse transmissions, effectively imrproving weather phenomena detection ranges.
  • and wave guide arc detection for high powered RADAR system

Saturday, January 28, 2012

Analysis of United 93 U-turn over Cleveland based on the ARINC logs

Posted by: Sergio

As explained in the introductory post, Warren Stutt and other people on Unexplained Mysteries claim, based on the ARINC logs publicly available, that the RGS (remote ground station) which actually transmits an uplink sent by the airline is indicated in the "Stn=" field within the first ULBLK block, while the RGS shown in the ULMSG block (which precedes the ULBLK block and represents the ACARS message as sent by the airline) only indicates the "predicted RGS" based on the original flight plan. One of the several problems with this claim is the fact that, if we accept this theory, then we must necessarily conclude that United 93 constantly flew within the Pittsburgh's RGS coverage area with no discontinuity from 9:23 EDT to 10:12 EDT without being detected by any other RGS with stronger signal for almost one hour. As anyone can easily notice reading through the 211 pages PDF of the ARINC logs, the station reported in the "Stn=" field in all the ULBLK blocks from 9:23 EDT until the end of the ACARS communications is always "PITC6", with the sole exception of a couple of occurrences for "Stn= IADA6" at 10:12 EDT in the final instants of the aircraft's ACARS log history. This raises the question as to how could United 93 possibly make the famous U-turn above Cleveland before disappearing from the radar screens as secondary track at 9:41 EDT in the vicinity of Canton, as reported by the 9/11 Commission (1), and yet never enter either in the Cleveland (CLE) or in the Akron/Canton (CAK) RGS coverage area.

In order to determine the distance of United 93 from the closest ground stations during the U-turn over Cleveland, I used the official radar positions for United 93 from 9:32 to 9:40 EDT (which corresponds to the time when United 93 allegedly made the U-turn over Cleveland), as provided by the 84 RADES Radar Data Spreadsheet released through FOIA. Then, I used GPS Visualizer to calculate the distance from the aircraft's position and the PIT, CLE and CAK remote ground stations respectively. Finally, I reported the resulting data into a Google Earth map to provide a visual representation of the Lat/Long position of the aircraft when messages #7, #8, #10, #11 and #12 were uplinked from the United Airlines dispatchers (2) and its distance from the closest ground stations.

Distance of United 93 from CLE, CAK and PIT remote ground stations at 9:35 EDT

Any blue aircraft icon on the map above represents the relevant position of United 93 as detected by the DTW radar site. The timestamp (i.e. 9:32) indicates the time of the radar hit. As anyone can notice at first glance, between 9:32 EDT and 9:36 EDT United 93 flew literally on the top of the Cleveland's RGS (CLE). After 9:37 EDT the aircraft began the second part of its U-turn heading SE to the direction of the Akron/Canton's RGS (CAK) while remaining at moderate distance from the CLE RGS. During this timeframe several messages were sent to the aircraft from UAL dispatchers, yet not one single occurrence for "CLEXX" or "CAKXX" is reported as "Stn=" in any ULBLK block, nor such transceivers appear as "BepStnName =" within any datalink from the aircraft (DLBLK), which is at the very least unexpected. Translated, this means that during its U-turn over Cleveland United 93 was not detected at any time by any Cleveland or Akron/Canton transceiver, but continued to communicate with the ARINC CPS through the Pittsburgh's station (PITC6), who was at more than 90 nm. Of course, it would be very interesting to analyze the radar hits after 9:40 EDT. However the last radar position available for United 93 before the hijackers allegedly turned off the transponder was detected at 9:40:03 EDT and was 41°00'38.662"N  081°51'46.830"W.

Position of United 93 at 9:35 EDT

Message #10 (according to the Winter's numbering) was sent by the UAL dispatcher Chad McCurdy exactly at 9:35 EDT. Therefore this message offers an excellent case study. As we can see from the map above, at 9:35 EDT the aircraft was literally flying over the CLE RGS. This is what Winter declared in 2002 in his interview to the FBI about this message:

Message #10 was from UAL flight Dispatcher CHAD McCURDY to the aircraft.
Message #10 was sent to the aircraft from CHIDD and was sent to the ACARS screen only. The RGS in this instance was near Cleveland, OH CLE from the line "AN N591UA/GL CLE..."

This is the log of this uplink as it appears from the printout of ACARS logs provided by Ed Ballinger to the 9/11 Commission:


;09111336 108575 0625

Finally, this is how the complete ARINC log for this message appears in the ARINC logs:

ARINC logs, p. 118

According to Warren Stutt and other posters on the Unexplained Mysteries' forum, the RGS shown after "AN N591UA/GL" field in the first log above (taken from Ballinger's logs) and the "Target Stn=" field within the ULMSG block (in the ARINC log screenshot) only indicate the predicted RGS, that is the RGS provided by the airline when the message is originally sent. In other words, it is the RGS expected after a certain time of flight according to the original flight plan. According to this theory, the RGS who actually transmits the ACARS is indicated in the first ULBLK block in the "Stn =" field. If this is true, then PITC6 and not any closer RGS transmitted the message sent by CHAD MCCURDY at 9:35 (as well as any other uplink until 10:12 EDT).

Using GPS Visualizer, I calculated the distance from the position of the aircraft at 9:35 EDT and the PIT, CLE and CAK remote ground stations. These are the Lat/Long positions shown on the map:

Aircraft/RGS Lat/Long position
United 93 at 9:35 EDT 41°20'17.89"N   81°58'55.62"W
PIT RGS: 40°29'29.40"N   80°13'57.72"W
CLE RGS: 41°24'38.88"N   81°50'58.18"W
CAK RGS: 40°54'53.70"N   81°26'10.69"W

And these are the distances between the above coordinates as determined by the GPS Visualizer's calculator:

United 93 at 9:35 EDT Distance (in nm)
PIT RGS (see red pointer A): 94.394
CLE RGS (see red pointer B): 7.4020
CAK RGS (see red pointer C): 35.455

If we believe to the claim supported by Stutt and other people on Unexplained Mysteries, the Pittsburgh's RGS had at 9:35 EDT the strongest signal although its distance from United 93 was 94.394 nm. For some obscure reason, the PIT station overrode both the Cleveland's RGS (CLE), which was at less than one tenth of its distance (7.4020 nm) and the Akron/Canton's RGS (CAK), who was at only 35.455 nm (i.e. well less than half the distance from PIT). If one has a minimal knowledge about how ACARS really work in the real world, the only possible conclusion after reading this data is that something definitely does not add up, either in the theory or in the data themselves. Giving priority to a station at more than 94 nm while having a station as close as 7 nm available and, in the event this were inoperative or temporarily unavailable due to congestion or any other interference, an alternative ground station at only 35 nm as a second option, is something we would definitely not expect from the CPS (the ARINC's Central Processing System that processes each and every message to and from any aircraft). At the very least, this situation is to be considered as highly abnormal, if not completely impossible. True is that there are sometimes instances where the closest station is not always the best station, for example in case of message collisions, terrain blockages, metropolitan interferences, temporary obstructions. Whenever the transmission through the best station is not successful, the message delivery occurs through a logical sequence of "next best" choices of stations. However, we know that the CLE and CAK ground stations were operative on the morning of 9/11, as testified by several occurrences for CLEA2, CLEB2 and CAKA2 in the "BEPStnName =" field both in the UA93 and in the AA77 log history. Actually what happens in the real world (and can be confirmed by any ACARS expert) is that the closest station is in almost 100% of cases the chosen station because of its signal strength.

Another claim raised by Warren Stutt and his followers on Unexplained Mysteries' forum is that the stations reported in the "BepStnName =" fields within the DLBLK blocks designate the ground stations "within range" at a particular time:

The DSP (ARINC) makes use of the location downlinks referred to in previous documents to keep its internal routing tables updated, but the airline does not. The DPSs use of this is evident by the ARINC 620-4 documentation and from the PDF supplied by Warren Stutt. In fact, Warren's PDF shows us a perfect example of the Category A network protocol in action with each DLBLK that you see following each ULMSG and ULBLK reference. The aircraft's omnidirectional transmissions are picked up by every RGS within range and it appears as though the routing table sequences a priority based on signal strength of those transmissions; the RGS with the strongest signal received is assigned as the initial station for future uplinks. This routing table is dynamically updated with each downlink from the aircraft, just as the previously uncovered reference material has described, and this is distinct from the static information (i.e. the GL text element which I outlined in my previous post) which is supplied by the airline dispatch in each message sent to the DSP for delivery.

I marked the most significant parts of the above claim in bold. The first one is "but the aircraft does not", which means that the targeted station reported in the ULMSG blocks is never dynamically updated by the CPS based on the actual positional data and always designates the expected RGS based on the flight plan. This claim is flatly contradicted by several cases that I will present in separate posts in the next future. However, for the purposes of the current analysis, it is more important to focus on the second claim marked in bold: "The aircraft's omnidirectional transmissions are picked up by every RGS within range". If this were true, then we would expect to see some references to Cleveland's and/or Akron/Canton's transceivers (such as "CLEXX", "CAKXX") which were clearly "within range" at 9:35 EDT as shown in the map. However, this is not what is actually reported in the ARINC logs. As we can see from the above screenshot, the alleged transceivers reported in the "BEPStnName =" fields refer to stations and locations which are very distant from the known position of the aircraft at 9:35 EDT, some of them being at nearly 200 nm, which is the maximum technical distance guaranteed by ARINC at FL290. These are the five transceivers reported in the DLBLK blocks:

BepStnName = YYZA6
BepStnName = YYZB6
BepStnName = YYZC6
BepStnName = PITA6
BepStnName = HTSA6

I reported these (alleged) ground stations on a Google Earth map including other possible alternative RGS that were closer to United 93 at 9:35 EDT but, for some reasons, were not detected by the aircraft and calculated their distance from the aircraft at 9:35 EDT using GPS Visualizer. This is the result:

Distance of United 93 from the transceivers shown in the "BepStnName=" field at 9:35 EDT

United 93 at 9:35 EDT Distance (in nm)
YYZ RGS (see red pointer D): 175.50 nm
HTS RGS (see red pointer E):  180.08 nm
TOL RGS (see red pointer F): 83.696 nm
FWA RGS (see red pointer G): 147.18 nm
DTW RGS (see red pointer H): 81.191 nm
CMH RGS (see red pointer I): 90.302 nm

So, let's take a look again at the screenshot from the ARINC logs and let's try to draw some conclusions after looking at the distances calculated by GPS Visualizer. The first three DLBLK blocks contain references to the Toronto ground station (YYZ). At 9:35 EDT the distance between the radar position of United 93 and the Toronto RGS was 175.50 nm. The fourth DLBLK block contains a reference to PITC6. As we have seen, at that time the distance from the Pittsburgh's RGS was 94.394 nm. Finally, the fifth DLBLK block reports a reference to Huntington (HTS), which at 9:35 EDT was at a distance of 180.08 nm.

Although all distances indicated above are technically within the 200 nm range, we should believe that the United 93's onboard ACARS MU not only completely ignored very close stations such as CLE (see pointer B), who was at only 7.4020 nm, and CAK, who was at a distance of only 35.455 nm (see pointer C), but also other relatively close RGS such as DTW (Detroit) (see pointer H), which was at 81.191 nm, TOL (Toledo) (see pointer F) which was at 83.696 nm, CMH (Columbus) (see pointer I) which was at 90.302 nm and finally FWA (Fort Wayne) (see pointer G) which was at 147.18 nm. Instead, United 93 apparently detected YYZ at 175.50 nm and HTS at 180.08 nm. Look at the same screenshot shown above with a zoom on the aircraft position:

Distance of United 93 from the transceivers shown in the "BepStnName=" field at 9:35 EDT. Zoomed view

It is obvious that something does not add up here. Claiming that "the aircraft's omnidirectional transmissions are picked up by every RGS within range" when several close stations are completely ignored and others as distant as 180 nm are detected means that either the theory is an unsubstantiated speculation or the data are not genuine and, therefore, nor reliable. 

One last example should conclusively clarify this issue. There is only one reference to the Cleveland's RGS in the DLBLK blocks related to United 93 log history:

ARINC logs, p. 93

As we can see, it is referred as "CLEA2" and is contained within a DLBLK block showing 13:03:06 UTC as timestamp, that is 9:03:06 EDT. Coincidentally there is a radar hit from the DAN site in the 84 RADES Radar Data Spreadsheet file which shows exactly the same Zulu time, 13:03:06,600. The radar position reported is 40°45'09.713"N   076°49'05.680"W. One more time this allows us to plot the relevant position of the aircraft on a Google Earth map and calculate its distance from the target using GPS Visualizer. This is the result:

Distance of United 93 from CLEA2 at 9:03 EDT

Again, the graphic and the distance data are self-explaining. According to the theory claimed by Stutt and others on Unexplained Mysteries, United 93 was able to detect the Cleveland ground station in a downlink at 9:03 EDT at a distance of 231.23 nm, which is well above the 200 nautical miles limit indicated by ARINC as maximum technical threshold for a successful ACARS transmission. But, for some incredible unknown reason, the CLE RGS was not close enough or its signal was not strong enough at 9:35 EDT to be reported in the "Stn=" field as the transmitting RGS while the aircraft was only 7 miles away and had literally flown over the Hopkins International airport one or two minutes before.

Position of United 93 at 9:40 EDT

Now let's take a look at the situation of United 93 at 9:40 EDT when Message #11 (according to Winter's numbering) was sent from United Airlines' dispatcher Ed Ballinger to United 93.

As mentioned above, the last officially known radar Lat/Long position for United 93 was tracked at 13:40:03,000 UTC (9:40:03 EDT) and was 41°00'38.662"N   081°51'46.830"W. This is when the alleged hijackers turned the transponder off. The aircraft was eventually monitored as primary track only. Now, Message #11 was sent by Ballinger at 9:40 EDT, 13:40 UTC. However, the message was probably delivered at 9:41 EDT, as confirmed by the line "BEPts=20010911 13:41:10" in the ARINC logs (FLoc=345838614, p. 119), which indicates then time when an uplink is received and processed by the ARINC CPS in Annapolis (the actual delivery to the aircraft normally occurs about ten seconds later). All the DLBLK blocks downlinked from the aircraft I will refer to below have a timestamp comprised between 13:41:12 UTC and 13:41:20 UTC. Therefore, in this case, the aircraft position represented on the map does not match exactly the actual position of the aircraft when the DLBLK blocks were downlinked. In other words, there is a little discrepancy of about one minute. Taking into account that the aircraft was headed Southwest at that time and that an aircraft expected to make a ground speed of 480 knots would cover 8 miles per minute or 1 mile every 7.5 seconds (240 NM in 30 minutes), we can assume that the position of United 93 at 9:41 EDT was up to 8 miles SW compared to the position shown in the map. This discrepancy is absolutely irrelevant given the magnitude of the distances shown below and has no significant impact on the conclusions of the resulting claim, however I thought it was correct to point out this issue before presenting the conclusion of this analysis.

As usual, Mr. Winter's statement will not be deemed as coming from an expert by Stutt and his friends on Unexplained Mysteries, although Winter worked as Manager of Flight Dispatch at United Airlines for 14 years having previously worked as Flight Dispatcher at Midwest Airlines from 1987 to 1990. Anyway, this is what he declared to the FBI about Message #11:

Messages #11 and #12 were sent to the aircraft from CHIDD using the RGS near Cleveland, OH. These messages also activated the audible signal in the aircraft.…

Giving for granted that "using the RGS near Cleveland, OH" will be one more time interpreted as "CLE was only the predicted RGS", let's take a look at the relevant printout coming from Ballinger's desk:

.CHIAKUA 111340/ED


;09111341 108575 0638

Finally this is the screenshot of the corresponding log in the ARINC log PDF. Please note that only the first part of this log is visible in the screenshot. This message is quite long, the header begins at the end of p. 118 and extends until the end of p. 120. Therefore please refer to the relevant pages in the document to have a full view of all the blocks contained in this message:

ARINC logs, p. 118

I reported the aircraft position at 9:40 EDT with the closer RGS' on a Google Earth map:

Distance of United 93 from CLE, CAK and PIT remote ground stations at 9:40 EDT

If we believe that "Stn=" indicates the actual transmitting station, then we must conclude that something very unusual happened one more time, just as we have seen at 9:35 EDT. At 9:40 EDT United 93 was very close to the CAK's remote ground station (20.229 nm), while CLE was an excellent second option at only 23.998 nm. Yet, we should believe that the CPS ignored two very close RGS' and arbitrarily routed Message #11 through PIT, which was at a distance of 80.596 nm, i.e. four times the distance compared to CAK and CLE. This is absolutely implausible and has no technical nor logical explanation. Moreover, since the position of the aircraft at 9:41 EDT was slightly more SW than shown on the map, as mentioned above, then we can conclude that United 93 was even closer to CAK. Therefore we would definitely expect to see a reference to the Akron/Canton RGS such as "CAKXX" in the "Stn=" field instead of "PITC6". But this is not what is reported in the ARINC logs.

If someone speculates that the Cleveland airspace was congested on the morning on 9/11 as explanation for the odd situation we have seen at 9:35 EDT, then he should also explain why the CAK's RGS was clogged or unavailable at that time as well. It is obvious that these "explanations" have no real technical basis. They are pure speculations which aim to support a theory which is simply wrong and contradicted by the same document it claims to be founded on.

However the bad news for the supporters of this theory do not end here. An analysis of the stations shown in the "BepStnName=" fields within the DLBLK blocks conclusively proves how poorly substantiated this theory is.

Distance of United 93 from the transceivers shown in the "BepStnName=" field at 9:40 EDT

These are the RGS' shown in the DLBLK blocks for this message and their distance from United 93 at 9:40 EDT:

Distance from United 93 at 9:40 EDT (in nm)
PITC6 80.596
IADC6 (pointer R) 238.05
YYZA6 (pointer T) 188.88
YYZB6 (pointer T) 188.88
HTSA6 (pointer S) 161.70
CRWA6 (pointer Q) 158.77
ORDA6 (pointer P) 278.46
DTWB6 (pointer U) 98.871
CVGA6 (pointer V) 174.29
YYZA6 (pointer T) 188.88
PITA6 80.596

One more time the aircraft appears to have been selectively "blind". While it was unable to see very close stations at only 20 nm such as CAK or CLE or other stations at a fairly distance such as TOL, incredibly he could see ORD (Chicago) at 278.46 nm and IAD (Washington, Dulles) at 238.05 nm, whose distance at 9:40 EDT was widely beyond the technical maximum threshold of 200 nm indicated by ARINC, and other stations such as YYZ (Toronto) at 188.88 nm, CVG (Cincinnati) at 174.29 nm, HTS (Huntington Tri-State) at 161.70 nm, CRW (Charleston) at 158.77 nm and DTW (Detroit) at 98.871 nm.

The only one possible conclusion after reviewing the above data is that either this theory is false or one of the following conditions applies:
  1. the radar data for United 93 were manipulated and the aircraft was not where the radar data claim it was (in which case, we must conclude that United 93 never made its famous U-turn over Cleveland, but kept on flying somewhere over the Pittsburgh, maybe in circles, for almost one hour) OR
  2. the ARINC logs, as publicly released, were manipulated and are not genuine

It is worth reminding that neither ACARS nor VHF transmissions are a guessing game. One cannot defeat laws of physics (electronics) with wishful thinking. How United 93 was able to "see" Chicago at 9:40 EDT at almost 280 nm while remaining blind to stations at less than 10 or 20 nm is honestly beyond me.

* republished with some edits from post #156 and post #165 on Pilots for 911 Truth  

(1) At 9:41, Cleveland Center lost United 93's transponder signal. The controller located it on primary radar, matched its position with visual sightings from other aircraft, and tracked the flight as it turned east, then south. Source: The 9/11 Commission Report, p. 46 (PDF version).
(2) The numbering of the ACARS messages follows Michael J Winter's interview in FBI302, p. 55-57.