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Member |
I'm curious about transponders in aircraft. This stems from a thread on another board about 9/11 and part of the conspiracy theories. The terrorists disabled the transponders in the aircraft after they hijacked them, effectively making the aircraft just another "blip" on the radar screen, but what aircraft are required to have transponders? Large airliners and military aircraft only, or small private planes and helicopters as well? I just wonder because I'm sick of hearing these conspiracy theory idiots talk about NORAD's "stand down" order,or whatever their stupid theory is, but if I understand correctly, air traffic control had no idea where the planes were after the transponders were disabled.
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Shaman |
I have to have a transponder to enter Class A, B C airspace.(and to utilize the E IFR corridors)
And to use flight following. My Beech only has a Mode C transponder. Oh and without a transponder, you're just a blip without a number.  A wise man's tools are analogies and puzzles. A wise man knows silence will speak for him. |
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Future Plane Pusher |
Per FAR Part 91.215
"A strong body makes the mind strong. As to the species of exercises, I advise the gun. While this gives moderate exercise to the body, it gives boldness, enterprise and independence to the mind. Games played with the ball, and others of that nature, are too violent for the body and stamp no character on the mind. Let your gun therefore be your constant companion of your walks." Thomas Jefferson to Peter Carr, 1785. |
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Future Plane Pusher |
As far as what we can see on radar, your just another primary target. We can see a dot, but we get nothing as far as altitude/speed. If your scope is filled with primaries, you won't be able to track a single target from the others.
"A strong body makes the mind strong. As to the species of exercises, I advise the gun. While this gives moderate exercise to the body, it gives boldness, enterprise and independence to the mind. Games played with the ball, and others of that nature, are too violent for the body and stamp no character on the mind. Let your gun therefore be your constant companion of your walks." Thomas Jefferson to Peter Carr, 1785. |
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Member |
Just trying to nitpick, I highly doubt that the terrorist did anything nefarious, they just turned the transponder off, or set it to standby.
------- Mr. Doom and Gloom Tacti-cool: adj - Any technique, firearm, or accessory that a person disagrees with. Example: Rails on an AR, that's tacti-cool. Synonym: Mall Ninjaish |
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Member |
I guess what I'm basically trying to figure out is, how many planes show up just as a dot on the screen vs. showing transponder information. Would it have been possible to track the planes after the transponders had been turned off, or would there have just been too much air traffic to figure out who was who?
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No More Mr. Nice Guy  |
Transponders send information, including a 4 digit number assigned by ATC, and your altitude. The controller enters the 4 digit number into the computer somewhere and tags it with your flight number or other identifying info for small aircraft. The altitude is self explanatory.
Airliners are required to have transponders on in all domestic airspace that we normally operate in while carrying passengers. If we turn off the transponder, the radar ground station only knows that there is a blip out there which is the radio waves bouncing off of something. The ATC computer loses the ability to know who we are or what altitude we are at. I don't know how sophisticated the 911 group were in their knowledge of transponders. However, it would make sense that they wanted their altitude to be unknown. If controllers thought that the airplanes were up high, it would lull authorities into thinking there was no threat to people on the ground. But if the altitude were known, someone might have seen the trajectory and accurately predicted what was about to happen. It may or may not be true that controllers did not know where the aircraft were. As I understand it, the display that the controller looks at is filtered, and he can show everything or he can limit what is shown. Controllers are working flights with transponders, so they don't want to see all the little dots (including trucks on the highway, really!). The screen the controller looks at is not a raw sweeping picture like the old movies, the info is collected from a number of ground radar sites and presented on his screen after being processed by computers. What are the conspiracy idiots claiming? That controllers were somehow in on the plan? ___________________________ Visit my family band page http://www.myspace.com/zozobramusic What would Jefferson do? Party like it's 1773! tyranny->revolution->freedom->prosperity->apathy->dependence->tyranny What would the Bull Moose do? |
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Member |
Well Fly-Sig, its tough to get inside an idiot's head, but I think the jist of what they think/say is that the controllers knew where the planes were the whole time, and that basically means the government knew where they were so they could have shot them down, but gave the "stand down" order. They like to use the phrase "stand down order" a lot! Maybe we should ask a conspiracy nut to join the thread and impart us with his or her wisdom? LOL
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Member |
Talk about conspiracy theories.
I just posted about how our (FAA) RADAR systems can track a primary target with some background info. I also posted that one of the 9/11 flights flew through out airspace. I went to edit my post to correct something and I got a message that the post was pulled due to a "trigger word". Oh noes! Did the Eschelon boys get me?? LOL. Quick answer, YES we can track a primary target(no altitude info) with our equipment as long as it's not an older system without the capability. habe |
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Member |
For a quick "snapshot" of current air traffic being tracked by US ATC, look at the "Live Flight Tracker" image HERE. It'll give you some idea of what the FAA's Flight Tracking Headquarters Bunker in Atlanta sees on a daily basis. Of course there will be more flights at certain times of the day and less at others.  P22, P220 (JJ), P226 (KA), P228 (KH), SP2022 (30Apr08), P232 (AF) |
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Political Cynic |
well, different modes of transponders relay different information.
A transponder has a small stub antenna usually located on the underside of the aircraft, and has a small ball on the top of it. The surface radar sends out a sweeping signal and when the transponder receives that signal, it replies with one of its own. This transmitted signal can contain a great deal of information. For example, all transponders can transmit a four digit code Mode C, for VFR traffic, the standard code would be 1200. You can request a discrete squawk code - say 2356, and when the controller see's your signal, he will see 2356 above the bars so you have been positively identified. IFR flights are all given individual codes. A Mode S transponder has the ability to transmit additional information such as registration information and flight data. Different codes have different meanings. For example, the universal emergency codes are 7500, 7600 and 7700. A procedure exists for pilots to transmit a hijack code or a communications failure code and then follow up with the 7700 code. The Constitution shall never be construed … to prevent the people of the United States who are peaceable citizens from keeping their own arms. – Samuel Adams "The problem with Socialism is that eventually you run out of other people's money." - Margaret Thatcher  |
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Political Cynic |
transponders can also transmit altitude info using a box called an altitude encoder, connected to a static port on the aircraft. It senses the barometric pressure, converts the altitude to a 'gray code' which is them encoded into the transponder signal
other aircraft equipped with a TCAS (a collision avoidance system) can actually read the signals coming from other aircraft, interpret the gray code, and display it in the cockpit to help give the pilot a 3-D representation of what the other aircraft are doing around him. It can also display whether or not the other aircraft are flying straight and level, ascending or descending The Constitution shall never be construed … to prevent the people of the United States who are peaceable citizens from keeping their own arms. – Samuel Adams "The problem with Socialism is that eventually you run out of other people's money." - Margaret Thatcher |
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Member |
ATC: skylane niner7 zero golf squack 2101 and ident
 How did I do? |
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Sigforum K9 handler |
I actually thought about all this sitting in the terminal at DFW on my way back from San Diego. Why not make the transponder something that has to be turned on/off by the ground crew on commercial flights, to keep terrorists from putting it in standby.
Oh, and by the way, my answer to end hijacking is expanding the Special Deputy US Air Marshal program to peace officers who volunteer to attend the training.  _______________________________________________________________________ Upcoming GGI classes www.grayguns.com Want free GGI training? Host a GGI class in 2010 and your tuition is free. |
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Political Cynic |
you did pretty good for a controller is squack the past perfect tense of squawk and is that particular term in the ATC Communications Handbook? how about 'squowking 2101' if used properly, the transponder can provide a discrete method of relaying info from the cockpit to ATC with non-verbal communications - would not be a good idea to allow the ground to be able to control the box The Constitution shall never be construed … to prevent the people of the United States who are peaceable citizens from keeping their own arms. – Samuel Adams "The problem with Socialism is that eventually you run out of other people's money." - Margaret Thatcher |
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Shaman |
I've used a transponder to communicate with a tower before when my radio wouldn't transmit.
I would use the ident button to affirm I understood instructions. A wise man's tools are analogies and puzzles. A wise man knows silence will speak for him. |
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No More Mr. Nice Guy |
Three reasons. 1) Airliners (and most turboprops and jets) have more than one transponder. If one fails, the other can be used. Because a transponder is required, if there is only one on board and it fails we are grounded. Many systems have backups for the very reason that if one fails we can continue revenue service. So it would become a very complicated system to have the control of the transponders done from the ground by remote control. 2) Equipment does fail. If the altitude information is incorrect, ATC will have the crew turn off the altitude transmission. The ATC computers use the altitude information for many functions, including predicting collision and for warning of being too close to terrain. Turning off altitude squawk is fairly common in general aviation, and for us it is switching transponders. It would become even more complex to enable remote control to do this. 3) In terms of terrorists on board, our transponder function is fairly irrelevant. Turning our transponder off in flight would not be enough to make us invisible, nor would it lull ATC into thinking all was well. Another 9/11 will never happen. The terrorists may find a way to bring down airplanes, but it will never be in any way similar to how they did it before. Our procedures as crew are completely different and far more effective than before, when we were instructed to comply with all demands. ATC procedures are different, law enforcement procedures are different, and military procedures are different. ___________________________ Visit my family band page http://www.myspace.com/zozobramusic What would Jefferson do? Party like it's 1773! tyranny->revolution->freedom->prosperity->apathy->dependence->tyranny What would the Bull Moose do? |
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