There is no evidence that there was a second United 175. United Airlines didn't say anything about a second United 175 flight, and there are no ATC communicaton transcripts clearing a second United 175 for takeoff from Boston nor ARTCC communication transcripts or transponder codes of a second United 175 flying in controlled airspace.
You are correct, there are however 2 different 'wheels off times' which to this day you write off as...Well what exactly?? A conspiracy wouldn't work very well if they made it too obvious...You seem to want them to admit they are about to pull the wool over our eyes...before they do so.
I'm sure if 2 different wheels off times proved your case, you would be all up in It's hood checking out the data wouldn't you skyeagle?
Why can such a pivotal, possibly immensely important piece of information be continually trodden underfoot? Do you actually have any interest whatsoever in looking for the truth?
It is a good point, and it is true. I shared it because it was interesting to me and I thought it might be interesting to others. I did NOT post it because I thought that it supported my case. I concede that the information could possibly indirectly support the hypothesis that Cz and I have presented, but it could also be completely unrelated. That concession has nothing to do with why I posted it.
Honestly, this is beginning to get tedious.
Considering that we're generally arguing from different points of view regarding ACARS, most of the stuff brought up here by you or me will probably be brought up because they support our stances. If you want to say that you brought it up solely for its interest value, ok, but I find it.. interesting that you find it may also support your stance.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
Scott G, on 09 December 2011 - 05:23 AM, said:
booNyzarC, on 08 December 2011 - 03:32 AM, said:
By the way Scott, I've noticed several times over the last few days where you have made statements that essentially convey your opinion that the time stamps on the ACARS messages from the FOIA document represent proof that the messages were delivered to the aircraft. Unfortunately, this hasn't been established as fact. I'm not going to say that they couldn't possibly be what you are assuming, but there is still the chance that this assumption is incorrect.
Ballinger, the United Airlines dispatcher who sent many of the messages in question, is the one who said it. Quoting him:
***In addition, Mr. Ballinger stated that the ACARS messages have two times listed: the time sent and the time
received.***
Show me where I've ever said that he didn't say that?
I never said that you said that he didn't say that (try saying that 3 times fast -.-)
booNyzarC, on 09 December 2011 - 06:10 AM, said:
You are arguing a point that I never made claim to...
Not at all. I'm trying to remind both you and the audience -who- it was that made that statement, as well as how unlikely it is that Ballinger would be wrong about it.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
Scott G, on 09 December 2011 - 05:23 AM, said:
The United Airlines dispatcher, whose job includes reading United Airlines ACARS messages, states that the 2nd time stamp refers to when the aircraft received the message and all you admit is that it's -possible- that what he says is true? How can it be anything other then highly probable?
So now you want me to quantify the level of possibility with an opinion?
Indeed.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
Would that help either of our arguments Scott?
It would.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
It is possible. To what degree it is possible, I don't claim to know. If you want my opinion, I'll give it, but it is only my opinion. I think it is highly likely that Ballinger didn't actually know the significance of the second time stamp and that he had always assumed that it indicated when the aircraft received the message. People make assumptions all the time and I won't put it past Ballinger to have done so. He's as human as anyone else. Again, that is merely my opinion.
Thank you. Now for a post on PFT written by onesliceshort that I sent Czero's way a while back that aids my point here:
*********
Just to add my 2cents on the alleged "printer timestamp" ...wtf would be the point of a printer timestamp when those on the ground would want to know at exactly what time the response was received? Or even sent in case of any future investigation (crash, mishap or accusation against aviation personnel both in the air and on the ground), or to make a call on whether they've received the message in time to avert the danger.
Say, for example, a warning was sent where the pilot had to divert from his course because of a weather front or even better warn them of possible hijackers on his aircraft and that they had to lock their doors (as were sent on 9/11), those on the ground would want to know the exact time that the message was received!
So yeah, I think it's pretty clear that Ballinger should have known what part of the message meant that the message was received by the aircraft; the fact that he states exactly what part of the message meant this confirms it.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
Scott G, on 09 December 2011 - 05:23 AM, said:
It is not an "assumption" that Ballinger stated that the second time stamp means when United Aircraft aircraft receive ACARS messages.
I never said that it was an assumption that Ballinger stated what he stated.
I never said you said this either.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
The assumption that I was referring to was your assumption that Ballinger was stating a documented fact and not his own assumption.
I think we should make this clear, as the probability that Ballinger knew what the second time stamp in ACARS messages meant is much higher then the probability that I would know what the second time stamp in ACARS messages meant without Ballinger's statement.
By the way Scott, I've noticed several times over the last few days where you have made statements that essentially convey your opinion that the time stamps on the ACARS messages from the FOIA document represent proof that the messages were delivered to the aircraft. Unfortunately, this hasn't been established as fact. I'm not going to say that they couldn't possibly be what you are assuming, but there is still the chance that this assumption is incorrect.
Your evidence for this is Ballinger's statement and nothing else.
Incorrect; there's also the fact that no one in a position to know has contradicted his statement. There's also the evidence that I've given in the past that UA 175 took off twice. There's also the evidence that UA 175 was going faster then an unmodified Boeing 767 could go at the time of the crash. There's more, but hopefully you get the point.
Remember, we're talking about the second time stamp here.
Actually, we're talking about the evidence for Ballinger's statement.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
No one in a position to know has contradicted [Ballinger's] statement? First of all, non-evidence isn't evidence.
A lack of evidence isn't necessarily evidence of its lack. Considering the importance of Ballinger's statement, it seems highly probable that if it weren't true, someone would have said something by now.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
Secondly, we have clear examples of messages that have a second time stamp which have been confirmed by Knerr and Winter to have NOT been received.
Not at all. We have clear examples of messages that have second time stamps which Knerr and Winter -think- were not received. But there's no indication that either of them knew what the significance of that second time stamp meant. If they -did- know and it contradicted Ballinger's statement, why didn't they say anything concerning Ballinger's statement?
booNyzarC, on 09 December 2011 - 06:10 AM, said:
Whatever evidence you think indicates that two aircraft took off has nothing to do with the second time stamp on the messages.
If it was just a matter of 2 aircraft taking off, that'd be one thing. But there's evidence that 2 aircraft took off that were both claiming to be UA 175. That suggests that a plan akin to Operation Northwoods was being conducted. Which, in turn, strongly suggests that Ballinger's statement was correct.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
If there's more evidence regarding the significance of the second time stamp, by all means share it.
No, that's all the evidence I have regarding the significance of the second time stamp. In terms of evidence backing up that the second time stamp meant what Ballinger states it meant, I just shared it.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
Scott G, on 09 December 2011 - 05:23 AM, said:
Again, why don't you opine on how -probable- it is that Ballinger, who probably read United Airlines ACARS messages every working day, could have mistaken what the second time stamp in a UA ACARS message meant.
I think it is highly probable that Ballinger held that assumption for a very long time.
Considering the apparent importance of knowing when aircraft receive ACARS messages, as explained by onesliceshort, I think it would be fair to call Balinger's statement indicative of his -belief- that the second time stamp meant the time that an ACARS message was received. It seemed way too important an issue for it to have merely been an assumption for Ballinger. By the way, I emailed ARINC asking them if the second time stamp was the time that the aircraft had received the message; I've gotten 2 'we'll get back to you's, but I have yet to actually get an answer. I believe you also sent ARINC an email; how's that going?
booNyzarC, on 09 December 2011 - 06:10 AM, said:
Consider the statements over on ATS by gman1972 who has apparently been working in a similar capacity for a long time. He didn't know what the time stamp meant either.
He's a dispatcher? In any case, Ballinger never said that he didn't know what the second time stamp meant. In fact, he stated what it meant quite specifically. As to gman, Balsamo had some things to say about him:
********************************************
...after thinking about this a bit more, I think gman himself doesn't really know (or is confused) regarding his own timestamps.
I went over to take another look, gman has posted his telex of the ACARS from his airline...
He claims the top ACARS is "... the identical format to the quoted acars messages [from United Airlines]."
Well, no, it's not.... for numerous reasons. The first thing which stands out is that he has two time stamps side by side on the bottom time stamp, including alpha text, while United ACARS do not.
I think he was told that the first time stamp is the sent time stamp, and the second time stamp is when the "printer" received the message. Gman translated this to meaning his printer in his office, when in reality, it probably means the printer on the flight deck in the aircraft, again, for his specific airline.
Either way, they aren't the same as United ACARS. Therefore, it is better to source a United Airlines Dispatcher regarding ACARS message timestamps from United Airlines, than some anonymous "gman" on some forum who readily admits himself "I have never claimed to be an expert in anything" combined with the fact he doesn't know anything about Cat A and B flight tracking, nor does he think it's important.
********************************************
Is it really all that implausible to accept the possibility that Ballinger didn't truly know the significance of the second time stamp?
I accept the possibility that Ballinger didn't truly know the significance of the second time stamp. I believe that possibility is quite small, however. When combined with all of the -other- evidence that the plane that crashed into the South Tower wasn't UA 175, that possibility becomes even smaller.
booNyzarC, on 09 December 2011 - 06:10 AM, said:
I'll tell you what though. If you can produce documentation which shows that the second time stamp on those messages was indeed the acknowledgement from the aircraft I'll happily accept that as valid evidence.
If I find such documentation, will do. In the meantime, I'll continue to wait and see if ARINC answers my question.
Can I ask which assumption you are referring to? It seems people are referring to an assumption Ballinger made that the second time stamp is a receipt from the aircraft. But I have not seen Ballinger make that specific assumption.
I think this is the statement referred to: -
Mr. Ballinger stated that the ACARS messages have two times listed: the time sent and the time received. He stated that once he sends the message it is delivered to the addressed aircraft through AIRINC immediately. He is not aware of any delay in the aircraft receiving the message after he sends it.
Is this where the assumption is interpreted?
The above statement leaves open that the receipt is received from the “aircraft” or “AIRINC” (more likely AIRINC in my opinion, as that is where Ballinger directly sends the message).
Am I missing something?
I don't think that you're missing anything Q24, and I agree that this is one possible way to interpret Ballinger's statement. This interpretation certainly does support the documentation that Cz has shared regarding two acknowledgements being sent back during the uplink process; the first (number 2 in the figure below) confirming that the DSP was able to successfully format the message for delivery through an RGS and the second (number 7 in the figure below) confirming whether or not the aircraft actually received it.
This interpretation of Ballinger's statement is consistent with the documentation and in my opinion is the best possible answer for the question of the significance of the second time stamp. That being said, it is also possible to interpret his statement differently, as Scott G has done, and this alternative is still also possible; albeit much less so. Regardless of the interpretation of Ballinger's statement, it is equally possible that he was conveying his own understanding and that his own understanding may not have been completely accurate, but rather a long held assumption.
No matter what though, the question itself remains unanswered from a definitive standpoint.
I don't think that you're missing anything Q24, and I agree that this is one possible way to interpret Ballinger's statement.
Thank you for the explanation.
It’s just that Scott keeps repeating along the lines…
Scott G, on 09 December 2011 - 12:27 PM, said:
Ballinger never said that he didn't know what the second time stamp meant. In fact, he stated what it meant quite specifically.
… and I thought perhaps I was missing a quote somewhere (where Ballinger specifically stated what the time stamp meant). My definition of specific is obviously different to Scott’s. I like to use the dictionary definition meaning “explicit” or “definite”. On this definition it is not specific where the second time stamp is receipted from, based on Ballinger’s statement.
Do you know, the more I read on this topic, the more I wonder what the argument actually is. I mean, there isn’t one. The ACARS messages fit as well if not better with the official version as it does a plane switch. It is not difficult to see. The whole thing is a non-argument.
Pilots for 9/11 ‘Truth’ leading us up the garden path yet again.
Operation Northwoods was a 1962 plan by the US Department of Defense to cause acts of violence, blamed on Cuba, in order to generate U.S. public support for military action against the Cuban government. The plan called for various false flag actions, such as staged terrorist attacks and plane hijackings, on U.S. and Cuban soil.
You are correct, there are however 2 different 'wheels off times' which to this day you write off as...Well what exactly?? A conspiracy wouldn't work very well if they made it too obvious...You seem to want them to admit they are about to pull the wool over our eyes...before they do so.
--
Question regarding the 2 different 'wheels off times'...
Do any of you know exactly what triggers the 'wheels off time' which is automatically sent through ACARS? This is part of the standard OOOI (Out, Off, On and In times) collected by the original implementation of ACARS and each 'time' is collected by a specific sensor when a specific event takes place, as depicted in this table.
OOOI Time....Action........................................Condition
Gate Out.....Aircraft leaves gate or parking position......Parking brake is released.
Wheels Off...Aircraft takes off............................Air/ground sensor on landing gear set to "airborne" state.
Wheels On....Aircraft touches down.........................Air/ground sensor on landing gear set to "ground" state.
Gate In......Aircraft arrives at gate or parking position..Parking brake is applied.
So the 'wheels off time' is when the Air/ground sensor on landing gear is set to "airborne" state. What does that actually mean?
It is supposed to indicate when the landing gear sensor is set to the "airborne" state, or when all of the wheels have left the runway during take off. It relies on the accuracy of the sensor to detect this "airborne" state. What happens if one or more of the landing gear is "stuck" even slightly? Suppose, for example, that it is possible that the particular sensor in question may have not accurately sensed this state and that it may have been triggered when the landing gear was raised?
I'm not saying that this is definitely what accounts for the apparent discrepancy, but I'm wondering if anyone has taken the time to look into this or other possible explanations for the supposed "two flight 175 theory."
It’s just that Scott keeps repeating along the lines…
Scott G said:
Ballinger never said that he didn't know what the second time stamp meant. In fact, he stated what it meant quite specifically.
… and I thought perhaps I was missing a quote somewhere (where Ballinger specifically stated what the time stamp meant). My definition of specific is obviously different to Scott’s. I like to use the dictionary definition meaning “explicit” or “definite”. On this definition it is not specific where the second time stamp is receipted from, based on Ballinger’s statement.
Do you know, the more I read on this topic, the more I wonder what the argument actually is. I mean, there isn’t one. The ACARS messages fit as well if not better with the official version as it does a plane switch. It is not difficult to see. The whole thing is a non-argument.
Pilots for 9/11 ‘Truth’ leading us up the garden path yet again.
Yes I agree, there are many assumptions in the P4T article and Balsamo misrepresents them as if they are facts. Most people capable of discernment will recognize this even after a cursory review of the evidence in question, but sadly many will just blindly take him at his word. The appeal to authority is a dangerous fallacy and I'd think that most people who support the 911 truth movement overall would recognize this fallacy above all others considering that it is the core basis for most 911 arguments against the "Official Version" which is viewed by many to be an appeal to authority in the first place.
So now you want me to quantify the level of possibility with an opinion? Would that help either of our arguments Scott? It is possible. To what degree it is possible, I don't claim to know. If you want my opinion, I'll give it, but it is only my opinion. I think it is highly likely that Ballinger didn't actually know the significance of the second time stamp and that he had always assumed that it indicated when the aircraft received the message. People make assumptions all the time and I won't put it past Ballinger to have done so. He's as human as anyone else. Again, that is merely my opinion.
Thank you. Now for a post on PFT written by onesliceshort that I sent Czero's way a while back that aids my point here:
*********
Just to add my 2cents on the alleged "printer timestamp" ...wtf would be the point of a printer timestamp when those on the ground would want to know at exactly what time the response was received? Or even sent in case of any future investigation (crash, mishap or accusation against aviation personnel both in the air and on the ground), or to make a call on whether they've received the message in time to avert the danger.
Say, for example, a warning was sent where the pilot had to divert from his course because of a weather front or even better warn them of possible hijackers on his aircraft and that they had to lock their doors (as were sent on 9/11), those on the ground would want to know the exact time that the message was received!
So yeah, I think it's pretty clear that Ballinger should have known what part of the message meant that the message was received by the aircraft; the fact that he states exactly what part of the message meant this confirms it.
I disagree. Nobody ever said that the significance of the second time stamp had to make sense. Just because a specific function is, or was, currently defined with a specific piece of information does not mean that the function in question could later be used for a different piece of information. In other words, the secondary time stamp could have been included with multiple possible uses and the actual implementation of that could vary between carriers and over time. The manual quote which gman1972 presented could have merely been the default setting for that particular field by the telex equipment manufacturer. Without the full manual and access to the equipment itself it would be hard to say.
At any rate, it isn't as definitive as onesliceshort is attempting to represent.
Scott G, on 09 December 2011 - 12:27 PM, said:
Actually, we're talking about the evidence for Ballinger's statement.
No, we are talking about the significance of the second time stamp; which has yet to be definitively determined. I guess I should clarify this though. I'm talking about the significance of the second time stamp. I was under the impression that we both were, but perhaps you are talking about something completely different, which I guess means that the additional points you raised aren't relevant to what I was actually talking about; which is my point.
Scott G, on 09 December 2011 - 12:27 PM, said:
A lack of evidence isn't necessarily evidence of its lack. Considering the importance of Ballinger's statement, it seems highly probable that if it weren't true, someone would have said something by now.
You really should stop with the assumptions Scott. It is perfectly alright to speculate, but when you interpret your speculations as though they are factual you are doing yourself a disservice.
Scott G, on 09 December 2011 - 12:27 PM, said:
Not at all. We have clear examples of messages that have second time stamps which Knerr and Winter -think- were not received. But there's no indication that either of them knew what the significance of that second time stamp meant. If they -did- know and it contradicted Ballinger's statement, why didn't they say anything concerning Ballinger's statement?
The interviewers did say something about Ballinger's statement though, didn't they?
[NOTE: TEAM 7 WILL RECEIVE BRIEFING BY AIRINC ON THE TIMING ISSUES INVOLVED FROM COMPOSITION OF THE MESSAGE BY THE DISPATCHER, TO TRANSMITTAL TO AIRINC, TO TRANSMITTAL FROM AIRINC TO THE AIRCRAFT, TO THE AIRCRAFT'S RECIPT OF THE MESSAGE.]
We just don't have the benefit of being able to review the detail of the briefing which is mentioned. I'd prefer to not assume what was in that briefing, but I'd be interested in seeing it if it ever becomes available.
The information from Knerr and Winters do contradict this interpretation of Ballinger's statement, which was my point. I'm not attempting to suggest that their statements overrule Ballinger's, just that they represent an apparent contradiction.
Scott G, on 09 December 2011 - 12:27 PM, said:
If it was just a matter of 2 aircraft taking off, that'd be one thing. But there's evidence that 2 aircraft took off that were both claiming to be UA 175. That suggests that a plan akin to Operation Northwoods was being conducted. Which, in turn, strongly suggests that Ballinger's statement was correct.
I haven't really looked into this claim in depth, but you might notice that I raised some questions about this theory a few posts ago. Perhaps I'll look into this in more depth later. But no, it has nothing to do with the significance of the second time stamp on those messages; which was what we have been discussing.
Scott G, on 09 December 2011 - 12:27 PM, said:
No, that's all the evidence I have regarding the significance of the second time stamp. In terms of evidence backing up that the second time stamp meant what Ballinger states it meant, I just shared it.
I thought so, thanks for clarifying.
Scott G, on 09 December 2011 - 12:27 PM, said:
Considering the apparent importance of knowing when aircraft receive ACARS messages, as explained by onesliceshort, I think it would be fair to call Balinger's statement indicative of his -belief- that the second time stamp meant the time that an ACARS message was received. It seemed way too important an issue for it to have merely been an assumption for Ballinger. By the way, I emailed ARINC asking them if the second time stamp was the time that the aircraft had received the message; I've gotten 2 'we'll get back to you's, but I have yet to actually get an answer. I believe you also sent ARINC an email; how's that going?
Actually I've sent ARINC 5 emails and I haven't had any response at all from any of them. Perhaps I was too direct about why I was asking the questions that I was asking, who knows. I don't blame them for not responding though. It could turn into a PR nightmare to have someone at ARINC misquoted or have their statements twisted into something that they weren't intended to implicate.
Scott G, on 09 December 2011 - 12:27 PM, said:
I accept the possibility that Ballinger didn't truly know the significance of the second time stamp. I believe that possibility is quite small, however. When combined with all of the -other- evidence that the plane that crashed into the South Tower wasn't UA 175, that possibility becomes even smaller.
Well, that's something I guess. At least you are open to the possibility.
Scott G, on 09 December 2011 - 12:27 PM, said:
If I find such documentation, will do. In the meantime, I'll continue to wait and see if ARINC answers my question.
You are correct, there are however 2 different 'wheels off times' which to this day you write off as...Well what exactly?? A conspiracy wouldn't work very well if they made it too obvious...You seem to want them to admit they are about to pull the wool over our eyes...before they do so.
I'm sure if 2 different wheels off times proved your case, you would be all up in It's hood checking out the data wouldn't you skyeagle?
Why can such a pivotal, possibly immensely important piece of information be continually trodden underfoot? Do you actually have any interest whatsoever in looking for the truth?
It has been determined that United 175 took off at 8:14, from Boston airport, and radar data and ATC communications confirm the takeoff time. Now, it has been said that wheels-off was at 8:23, which is incorrect because ATC would never allow two aircraft with the same tail number from the same airline to takeoff within minutes of one another for obvious safety and other reasons, so it comes down to the switch. Switches do malfunction from time to time and I can remember when we were grounded at Kadena airbase, Okinawa, because of a bad anti-lock switch. We were grounded overnight until a replacement switch was flown in aboard a C-141 and installed on our aircraft.
Since we can safely determine the actual takeoff time of United 175 from Boston airport using radar data and ATC communication transcripts between the flight crew and air traffic controllers at 8:14, for which there are none for a takeoff time of 8:23, we need to take a look at the switch because switches do malfunction and fail from time to time.
Edited by skyeagle409, 09 December 2011 - 09:09 PM.
"Truth needs no defence. Nobody - NOBODY - can ever take the footsteps I made on the surface of the Moon away from me."
Gene Cernan, Apollo 17
Posted 10 December 2011 - 12:28 AM
Wandering, on 09 December 2011 - 12:16 PM, said:
You are correct, there are however 2 different 'wheels off times' which to this day you write off as...Well what exactly??
That is absolutely normal. For instance, at the end of each month our Times and Stats officer goes through our authorisation forms, checking the takeoff time and flight time against what is recorded in our maintenance system, CAMM2. There are ALWAYS discrepancies.
Another example is landing charges. Defence still has to pay landing charges at civil airports (though under the letter of the law we are exempt, but the PTB choose to ignore that). Each month or so a list of military aircraft landings at civil airfields is sent through for confirmation, before the necessary charges are paid. Should be pretty easy, as ATC will have an aircraft type, the callsign and sometimes the side number, as well as the normal info like when and where.
Often we have a Navy callsign with no record of Navy being there. Sometimes it is an Army callsign with an Army aircraft type, but matches the the, location and activity of a Navy aircraft. Sometime neither Service has any record matching the claimed movement.
So there were two times recorded? Ops Normal, if you ask me.
Perhaps it would be more helpful to understand our hypothesis if there were some images to help visualize the concept.
Consider this image which shows the full flight path of United 175 compared with an estimation of the original flight plan and the locations of several RGS stations.
First, notice that the original flight plan would have taken UA175 directly over Pittsburgh as it continued west. This is represented by the solid red line and I estimated the general path from an image originally published by USA Today, viewable here. By my estimates the aircraft would have been very close to Pittsburgh by 9:23 AM if it hadn't been hijacked.
Second, notice that from about 8:45 until about 8:51, UA175 was flying almost directly toward MDT RGS.
Third, notice the range of MDT depicted by the large red circle. UA175 entered this 200NM range somewhere around 8:37 and according to the radar data, it never left that range.
And consider this image which is panned a bit closer.
I've drawn three lines from MDT to certain radar points for different reasons.
The first line is to where UA175 was at about 8:51, roughly 84NM from MDT. This is to hi-light the absolute earliest that MDT could have been acquired as the legitimate RGS provided there was no successfully completed downlink request to update the CPS table made up until the time of the impact with the WTC sometime between 9:02:57 and 9:03:11.
The second line is to where UA175 was at about 8:53, roughly 76NM from MDT. This is a somewhat more reasonable earliest point than the first given that the standard interval between automatic downlinks is purportedly about every 10 minutes. Interestingly this is also the general time when UA175 comes the closest to MDT.
The third line is to where UA175 was at about 8:59, roughly 124NM from MDT. This is significant because this is about when Jerry Tsen's message is reported to have been successfully received by the aircraft.
For this hypothesis to be possible it requires that UA175 was relying on a Category A network and not a Category B network. Some may recall the claim that Commercial Airlines use Category B protocol by Valkyrie in post 1103, but he has offered absolutely zero evidence to support this claim. Among the many documents I've looked through over the last couple of weeks, I've found the following which I think might suggest otherwise...
There are two categories of operation for VHF ACARS: Category A, used by ARINC and Category B used by SITA.
I haven't seen any references to SITA in the FOIA documents, so I'm fairly certain that the investigation only involved the airlines and ARINC. I'd have to go back and review more to be certain, but I'm also pretty sure that the bulk of SITA's expansion into the US was well after 2001. If this entry from the PDF is accurate, that pretty much rules out the possibility that UA175 was relying on a Category B protocol. The approval date for this document is July of 2001, so even if ARINC has adopted Category B protocols since then, we can tell that they hadn't done so by less than two months prior to September when this event took place. The same information can be found on page 58 of this document, but it is dated in May of 2000.
I have been thinking about compiling much of this (and more) into a blog entry but I haven't really gotten around to it. Rather than further delay the sharing of this information by procrastinating about whether or not to make a blog, I'll just post it here for now. I may revisit the blog idea later and more fully flesh out the hypothesis in one single place. Here are the links to several previous references about this hypothesis for anyone looking for it:
For anyone interested, I've included some additional references below which may help to understand the technologies involved and make a little more sense of the arguments for both sides. The references are a bit long, so I'm enclosing them in spoiler tags.
Forgive the formatting, it is just a copy/paste from a text file.
Spoiler
References:
**** On The Position of the Aircraft and RGS Locations ****
5.3.2 ARINC Internetworking Function, Routing, and Use of Media Advisories, and Prioritization
ARINC’s GLOBALink® Service includes three Back-End Processors (BEPs) located in Annapolis, USA; Beijing, China; and Bangkok, Thailand. The Annapolis BEP controls SATCOM and HFDL networks as well as AOA and VHF ACARS networks in Americas, Europe, Middle East and Africa. Beijing and Bangkok BEPs manage VHF ACARS networks in Asia.
Internetworking functionality implemented at ARINC is applicable to all ARINC networks described above as well as the SITA network. ARINC determines routing algorithms for uplinks originated by FANS ATSPs connected to ARINC networks based on media advisory information. If media advisory information is available, then preference is given first to VHF, then SATCOM, and then HFDL. If media advisory information is not available then uplink routing decision is made based on last successful delivery. If no messages have been delivered to/from aircraft within last twelve minutes then ARINC makes FANS uplink routing decision based on static information, which can be configurable by customer’s request.
Ballinger stated that it is not the dispatcher's job to monitor tracking of the flight path. The flight path information he has is not actual radar data but is a system that anticipates where the plane would be given its flight plan etc. It's the job of FAA Air Traffic Control to keep track of the flight path, and if it isn't going where it's supposed to then ATC notifies the air carrier's corporate office. He noted that the receipt of some information made [redacted] query Flight 93 at 9:03 and it was probably a call from ATC saying that we're having a problem.
2.3.7. ACARS Mobility
Mobility in ACARS system is simplified due to its centralized nature. All ACARS messages pass through a central node (or central processor). The central node has the ability to track all messages and determine where the aircraft is located at all times. The process by which mobility in ACARS is implemented is quite simple and can be illustrated in the following steps:
• ACARS downlink (from aircraft to ground)
– An ACARS messages is received by a VHF, HF or SATCOM ground station.
– Upon receipt of the downlink, the ground station forwards the ACARS message to the system central node for processing and routing.
– The central node, upon receiving the ACARS downlink, forwards the message to the appropriate stationary end system.
• ACARS uplink (from ground to aircraft)
– An ACARS message transmitted from a stationary ground end-system is received by the central node.
– Upon receipt, the central node forwards the message to the appropriate ground station for transmission. The central node chooses the ground station based on criteria such as best signal quality or other determining factors.
– The ground station, upon receiving an uplink message from the central node transmits the message to the aircraft.
3.2.1.1 ACARS / VDL mode 1
The ACARS communications sent via VHF radio or via satellite go through a network of ground stations linked via a terrestrial data network to a centralized data link service processor, which provides the interconnection to the ground systems of the airlines. The ACARS data link service processor routes messages automatically between the user aircraft and ground systems, using mostly a fixed configuration of delivery addresses by message type for downlink messages and by memorizing the ground station to be used for uplink messages. The main restriction on the ACARS system is that it uses the character codes defined by standards such as ASCII, and the user data field can only transport the codes representing printable characters. This limitation applied to all data communications systems when ACARS was first implemented in the late 1970s. Besides, the ACARS performance is far too unpredictable for general ATC use, especially in high density airspace. This is firstly because the overall bit rate at 2.4kbps (shared by all aircraft in a given airspace) is too low to support both Air Traffic Control (ATC) and Aeronautical Operational Control (AOC) communications but also because ACARS is poor at keeping track of aircraft. ACARS keeps track of aircraft by remembering which Ground Station (GS) in its worldwide network of VHF Ground Stations received the last downlink from a given aircraft. It then uses that GS for the next uplink for that aircraft. However, the aircraft could have gone out of range of that GS between the downlink and subsequent uplink. ACARS will retransmit several times before realising this and then “hunt” for the aircraft by attempting the uplink for nearby GS. The result is an unpredictable uplink delay.
2.3.1.1.ACARS
The Aircraft Communication Addressing and Reporting System (ACARS) VHF data link has been in operation for the last twenty years and has enabled a wide variety of Airline Operational and Air Traffic voice communications to migrate to data. Majorities of the airlines now depend on ACARS data link for their operations. However, the existing ACARS system has some inherent protocol limitations that prevent VHF communications to be limited to 2400 bps data rate. The effective throughput is usually even lower – sometimes in the order of 300 bps.
Although ACARS permits the exchange of data, it is a character oriented system more suited to textual data only. It is an analog system with analog AM-MSK (Amplitude Modulation – Minimum Shift Keying) as the modulation. The limited graphical weather capability is made possible by the use of compression algorithms which reduce a limited graphic file into a character string before transmission over the current ACARS infrastructure. ACARS will eventually be replaced by digital links such as VDL-2 but aircraft will potentially operate in mixed mode environment for years to come because the ground infrastructure will be upgraded over a period of time.
ACARS uplink (from ground to aircraft).
The central node receives an ACARS message transmitted from a stationary ground end-system.
Upon receipt, the central node reformats the message into the air-ground protocol, determines the destination aircraft (because of how aircraft can be addressed, errors are made in the lookup), and forwards the message to the appropriate ground station for transmission. The central node chooses the ground station based on criteria such as best signal quality or other determining factors. However, because aircraft transmit at a slower rate when they transition between ground stations, a fairly high percentage (3-5%) of messages cannot be delivered as the system has lost track of the aircraft.
The ground station, upon receiving an uplink message from the central node, transmits the message to the aircraft.
(It then goes on to discuss the improvements of VDL Mode 2, but this wasn't implemented anywhere in the US until 2002, and even then it was only initially implemented in Florida.)
THE USE OF TRACKER MESSAGES IN CATEGORY A ACARS NETWORKS
Many customers frequently ask about the purpose of tracker messages: “What are tracker messages?” “How are tracker messages used?” This article provides answers to those questions.
Description and Purpose of Tracker Messages
Tracker messages are VHF ACARS downlinks that are sent automatically at fixed intervals, typically 10 minutes. These messages allow the service provider to dynamically track aircraft during flight. In most cases, the avionics use a Q0-labeled Link Test as a tracker message. The Link Test message does not contain any useful application text; therefore, it does not result in a delivery message to the airline customer. Some customers prefer a user-defined tracker message with a message label other than Q0. The message may include additional information such as geographic position or altitude within the message text. These user-defined messages certainly would be delivered to the airline host computer.
As mentioned, tracker messages are used for flight following. Each time a downlink message is received from an aircraft, the ARINC ACARS Central Processor System (CPS) is updated with the three best remote ground stations (RGSs) that received the downlink message. When ARINC receives an uplink message from the airline computer, it first consults a table in CPS to determine which stations are most likely in contact with the aircraft. It tries these stations for message delivery. If no downlink activity has been heard from the aircraft in 11 minutes, the CPS system returns the uplink back to the originator as undeliverable.
For aircraft in flight, the CPS holds the RGS station information as active for only 11 minutes. After that time, the station information is deleted because an en route aircraft will usually have moved on to a different set of stations. When an aircraft uses 10-minute tracker messages, CPS is continuously refreshed with new RGS information and always knows where to deliver an uplink message.
If an airline sends uplink messages only after they have been specifically requested by a downlink from the aircraft, then tracker messages may not be needed. This is because the preceding downlink request automatically updates the ground network with aircraft location information. An uplink message that was not first requested by the aircraft (by downlink) is referred to as an “unsolicited uplink.” For unsolicited uplinks, CPS knowledge of the best RGSs is essential to successful delivery of the message. In practice, almost all airlines send some unsolicited uplinks and depend on the service provider to know what RGSs are in communication with the aircraft.
Category B Networks and Tracker Messages
In a Category B network, the traditional tracker message is considered optional because the tracker message function is covered elsewhere in the air/ground protocol. This would lead some to believe that a Category B network operates more efficiently by not using traditional trackers.
In a Category B network, aircraft must monitor all the stations available and then select a single station to establish a connection to the ground. During the connection process, the first action of the avionics is to send a Link Test to establish a connection with the RGS.
This Link Test has a format that is identical to the Category A tracker message. Once the connection is established, messages to the aircraft are handled by this single RGS.
With Category B, the aircraft can only connect to one RGS at a time; therefore, during flight the avionics must change RGS connections and repeat the connection process every few minutes. As a result, while the traditional tracker function is not needed, Link Test messages are still transmitted at frequencies that are at least the same or greater than those used in a Category A network.
Summary
Tracker messages allow ARINC’s Category A VHF network to track an aircraft during flight and allow us to make the best RGS selections for message delivery. Tracker messages do not decrease the network efficiency and are recommended for customers that send unsolicited uplink messages. Many avionics systems allow an airline to enable tracker messages as a maintenance or configuration item. As always, please contact us if you’d like further information or assistance in enabling tracker messages in your aircraft.
There are two categories of operation for VHF ACARS: Category A, used by ARINC and Category B used by SITA. Satellite communications is treated as a special case of Category A. Switch-over between the VHF and satellite media is discussed in sections 7.3.2.6 and 7.3.3.
The main differences between the categories are in their handling of downlink messages.
With Category A, all RGSs within range of an aircraft receive the transmitted message and onforward it to the DSP. Received signal quality derived from the downlink is then used in selecting the RGS for any uplinks including Acknowledgments.
With Category B, downlink messages are addressed to a particular RGS. The Airborne Communications Management function obtains RGS addresses from regular transmissions known as a "squitters", which are provided by each RGS for acquisition and identification purposes.
There are two categories of operation for VHF ACARS: Category A, used by ARINC and Category B used by SITA. Satellite communications is treated as a special case of Category A. Switch-over between the VHF and satellite media is discussed in sections 7.3.2.6 and 7.3.3.
The main differences between the categories are in their handling of downlink messages.
With Category A, all RGSs within range of an aircraft receive the transmitted message and forward it to the DSP. Received signal quality derived from the downlink is then used in selecting the RGS for any uplinks including Acknowledgments.
With Category B, downlink messages are addressed to a particular RGS. The Airborne Communications Management function obtains RGS addresses from regular transmissions known as a "squitters", which are provided by each RGS for acquisition and identification purposes.
For satellite communications, the task of acquiring a suitable GES for communication is handled by the SDU. As no special addressing is required by the DCMF, satellite communications appear as Category A.
The DCMF can operate with both Category A and Category B networks.
ACARS communications are divided in Category A and Category B.
Using Category A, an aircraft may broadcast its messages to all ground stations. This is denoted by an ASCII "2" in the Mode field of the downlink message. The WAVECOM software translates this character to "A".
Using Category B an aircraft transmits its message to a single ground station. This is denoted by an ASCII character in the range "@" to "]" in the Mode field of the downlink message.
The ground station may use either "2" or the range "‘" to "}" in the Mode field. All ground stations support Category A, but may uplink "‘" to "}" in the Mode field.
**** Some Videos Related to ACARS ****
**** Ref 1 ****
From URL:
Audible example of ACARS transmissions.
**** Ref 2 ****
From URL:
Audible example of ACARS transmissions. Also shows software decoding in action.
I've collected much more than this, but over the last couple of days I started to organize it a little better. Hope this information is of value to someone, it has taken some work to track these things down and there is more to find.
Cheers.
Edit to mention that much of the reference material for this is from Cz's diligent research. I'm not trying to claim ownership to all of the references presented.
Question regarding the 2 different 'wheels off times'...
Do any of you know exactly what triggers the 'wheels off time' which is automatically sent through ACARS? This is part of the standard OOOI (Out, Off, On and In times) collected by the original implementation of ACARS and each 'time' is collected by a specific sensor when a specific event takes place, as depicted in this table.
OOOI Time....Action........................................Condition
Gate Out.....Aircraft leaves gate or parking position......Parking brake is released.
Wheels Off...Aircraft takes off............................Air/ground sensor on landing gear set to "airborne" state.
Wheels On....Aircraft touches down.........................Air/ground sensor on landing gear set to "ground" state.
Gate In......Aircraft arrives at gate or parking position..Parking brake is applied.
So the 'wheels off time' is when the Air/ground sensor on landing gear is set to "airborne" state. What does that actually mean?
It is supposed to indicate when the landing gear sensor is set to the "airborne" state, or when all of the wheels have left the runway during take off. It relies on the accuracy of the sensor to detect this "airborne" state. What happens if one or more of the landing gear is "stuck" even slightly? Suppose, for example, that it is possible that the particular sensor in question may have not accurately sensed this state and that it may have been triggered when the landing gear was raised?
I'm not saying that this is definitely what accounts for the apparent discrepancy, but I'm wondering if anyone has taken the time to look into this or other possible explanations for the supposed "two flight 175 theory."
Thanks for the info Boony, do you happen to recall seeing this discussed in any of the documents you have read. The article doesn't go into much detail is all.
For example, If it is set to an 'airborne' state, that means it has to switch back to 'ground state' to come back to 'airborne' state again. I'm just wondering what this would entail, if there are safeguards in the program to detect If it's on the ground or in the air. Great find though
skyeagle409, on 09 December 2011 - 09:04 PM, said:
It has been determined that United 175 took off at 8:14, from Boston airport, and radar data and ATC communications confirm the takeoff time. Now, it has been said that wheels-off was at 8:23, which is incorrect because ATC would never allow two aircraft with the same tail number from the same airline to takeoff within minutes of one another for obvious safety and other reasons, so it comes down to the switch. Switches do malfunction from time to time and I can remember when we were grounded at Kadena airbase, Okinawa, because of a bad anti-lock switch. We were grounded overnight until a replacement switch was flown in aboard a C-141 and installed on our aircraft.
Since we can safely determine the actual takeoff time of United 175 from Boston airport using radar data and ATC communication transcripts between the flight crew and air traffic controllers at 8:14, for which there are none for a takeoff time of 8:23, we need to take a look at the switch because switches do malfunction and fail from time to time.
Yawn.
Aren't you even a little embarassed that you are supposed to be an expert on planes, yet you have ignored this question until provided a possible answer by someone else? You then jump on it and claim that to be true. Why not mention the switches..oh...50 odd pages ago on the 20 odd times It's been bought up? The more you talk I doubt your expertise.
Obviousman, on 10 December 2011 - 12:28 AM, said:
That is absolutely normal. For instance, at the end of each month our Times and Stats officer goes through our authorisation forms, checking the takeoff time and flight time against what is recorded in our maintenance system, CAMM2. There are ALWAYS discrepancies.
Another example is landing charges. Defence still has to pay landing charges at civil airports (though under the letter of the law we are exempt, but the PTB choose to ignore that). Each month or so a list of military aircraft landings at civil airfields is sent through for confirmation, before the necessary charges are paid. Should be pretty easy, as ATC will have an aircraft type, the callsign and sometimes the side number, as well as the normal info like when and where.
Often we have a Navy callsign with no record of Navy being there. Sometimes it is an Army callsign with an Army aircraft type, but matches the the, location and activity of a Navy aircraft. Sometime neither Service has any record matching the claimed movement.
So there were two times recorded? Ops Normal, if you ask me.
I don't doubt you get discrepancies, but in this particular circumstance with what has been proposed it needs to be examined further to see if it was a discrepancy or whether It was the result of something more sinister.
According to skyeagle, this would be impossible as at any given time at any given second everyone knows what plane is at the airport they would have their tail number and the flight would not be allowed in and there would have to be a record of the flights because otherwise alarmbells would be ringing and then alarmbells would be ringin at the FBI all because there is a different plane there. *BREATHES*
Quote
So there were two times recorded? Ops Normal, if you ask me.
Do you mean...Normal for an operation? Because we are talking about civilian flights here...not a Military operation...or are we?
So the 'wheels off time' is when the Air/ground sensor on landing gear is set to "airborne" state. What does that actually mean?
It is supposed to indicate when the landing gear sensor is set to the "airborne" state, or when all of the wheels have left the runway during take off. It relies on the accuracy of the sensor to detect this "airborne" state. What happens if one or more of the landing gear is "stuck" even slightly? Suppose, for example, that it is possible that the particular sensor in question may have not accurately sensed this state and that it may have been triggered when the landing gear was raised?
My understanding is that the "wheels up" message is triggered by sensors on the nose wheel, or possibly on all landing gear struts. I read a brief description of it in one of the several hundred documents / webpages I've read through in the past few weeks.
A very simplified way to look at aircraft landing gear is that they are essentially just like the shock absorbers in a car, except a LOT larger. When on the ground, the landing gear is under compression from the weight of the aircraft. When the wheels come off the ground, the landing gear extends, in the same way that when you lift a car off the ground, the wheels drop as the shock absorbers / struts extend. Sensors on the landing gear are triggered when they reach a certain extension, most likely their fully extended position.
In the same way that a message is generated when on-board sensors detect that the cabin doors are closed and when the aircraft's parking break is released when it is pushed back from the gate, the landing gear sensors initiate a "wheels up" message showing the exact time the aircraft lifted off the runway.
Cz
"Thinking is critical, because sense is not common..." - GreaterSapien
"Enquiring and doubting the "official story" are also good things ....However when these doubts require you to ignore the evidence, to dishonestly cherry pick evidence and claim it supports your case when it doesn't, when you operate a double standard; demanding proof of that which is already proven whilst making unsupported statements and personal opinions to back your own case and when you deny the truth simply because it IS the official story then you are no longer acting in a rational way. This is not the behaviour of a "different thinker", this is the behaviour of a "believer" who chooses not to rationally think about the evidence at all." - Waspie Dwarf
Cheers Cz, that is pretty much my understanding as well. I've not devoted a great deal of focus on this particular aspect over the last couple of weeks, but I've seen similar references.
Wandering, on 10 December 2011 - 03:47 AM, said:
Thanks for the info Boony, do you happen to recall seeing this discussed in any of the documents you have read. The article doesn't go into much detail is all.
For example, If it is set to an 'airborne' state, that means it has to switch back to 'ground state' to come back to 'airborne' state again. I'm just wondering what this would entail, if there are safeguards in the program to detect If it's on the ground or in the air. Great find though
--
Sure thing Wandering, I've read a bit about it here and there. Most of what I've read is regarding how it is supposed to work, but like everything in life; sometimes things don't work the way that they are supposed to. I think that might have been the intention behind skyeagle's post as well by the way. Whenever you are relying on sensors to tell you something, it is possible for those sensors to give you the wrong signal at the wrong time.
Consider these additional details from a patent (not regarding the patent, but regarding the actual "wheels off" event itself.)
First, there is some background given regarding how OOOI events have been recorded, including both ACARS and recordings taken by hand.
Currently, some airlines require their flight crews to record OOOI times by hand on a per flight basis. The flight crew then verbally relays the "Out" and "Off" Times after departure to their ground based dispatch operations via their VHF Transceiver. Upon arrival, the flight crew hand delivers the written "On" and "In" Times to the gate agent, who subsequently enters the times at a computer terminal. The Captain's Clock in the flight deck is used as the time source. Other airlines use an Aircraft Communications Addressing and Reporting System (ACARS) Management Unit (MU) and VHF Transceiver to automatically forward OOOI times to their ground based dispatch operations. The ACARS approach has some drawbacks. Passenger and cargo doors are typically wired with sensors that detect door closure. The parking brake also has to be wired with a sensor to detect when it is released or set. These discrete wires have to be installed and routed to the ACARS MU, along with the landing gear squat switch discrete, to provide it the information it requires to define the OOOI times. The cost of using the ARINC provided ACARS service to forward OOOI times is expensive by commercial wireless telecommunication standards. The cost associated with ACARS is what motivates some airlines to favor the manual approach.
Next, it talks about the Air/Ground Relay...
The Air/Ground Relay is monitored to detect the precise moment when the aircraft wheels leave the runway. This time is recorded as the "Off" Time, i.e., weight off wheels.
A little more detail about the "Wheels Off" time is provided further on.
The "Off" time is defined by the moment the aircraft's weight is off the landing gear. An Air/Ground squat switch is mounted to the landing gear and used to detect the weight off wheels and the weight on wheels. ARINC defines the "Off" time as the moment when the sanding gear switch first annunciates the extension of the strut followed by 10 seconds of continuous strut extension.
If you take the time to read through the whole patent, you'll see that this system is far from perfect and has enough room for error that it isn't implausible to consider that discrepancies are completely possible and do in fact happen. Many improvements to this system have most likely been implemented over the years, but how accurate was it a decade ago? Good enough for most, I'd bet, but certainly not spot on all the time.
Aren't you even a little embarassed that you are supposed to be an expert on planes, yet you have ignored this question until provided a possible answer by someone else?
Nope!!
It is all just a matter of common sense in the world of aviation, which you are not tuned into because you are not aware of the way things work in the real world. When I said that the actual takeoff time of United 175 was determined from radar data and ATC communications, which we didn't have for 8:23, it should have been evident that the problem was on the aircraft and it was all very simple.
When I said that ATC would not have cleared another flight with the same tail number of the same airline within minutes of one another at the same airport, that should have given you another clue, but apparently, you missed the boat on both occasions.
May I suggest that you don't ridicule that, for which you have no understanding.
Edited by skyeagle409, 10 December 2011 - 04:51 AM.
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