IFF Beacon

[John Doe II]

Can somebody please help me out on this?

I'd like to know what the IFF Beacon is and if all commercial planes do have it.
Moreover does anybody of you have an idea why AA 11 switched off its IFF Beacon. What did the hijackers gain by doing this? And why didn't the other three planes follow?

Thanks a lot in advance,

John Doe II

[spooked911]

1. IFF beacon is the same thing as the transponder

IFF stands for "Identify Friend or Foe".

My understanding is that it started out as a military device then started being used on commercial planes as well to keep track of them.

I assume you know the transponder story for the 9/11 flights.

[John Doe II]

2. Thanks Spooked911,

:)
but I believe that IFF Beacon is somewhat different from the transponder as everywhere is stated that only AA 11 switched off its IFF Beacon.
Therefore what exactly is the IFF Beacon?
What's the advantage off switching it off?
Why didn't all four planes switch it off as they switched off the transponder?

[hack89]

3. Spooked911 is right IFF = transponder

[John Doe II]

4. According

to Paul Thompson's Timeline the transponder of AA 11 is switched off at 8:13 but the IFF Beacon at 8:20.

[hack89]

5. From Wikipedia

In telecommunications, identification, friend or foe (IFF) is a system using electromagnetic transmissions to which equipment carried by friendly forces automatically responds, for example, by emitting pulses, thereby distinguishing themselves from enemy forces.

The primary use of the term is to describe an aviation subsystem that permits military aircraft, and both civilian and military air-traffic controllers, to identify aircraft as enemy and friendly, and track them.

The fundamental mechanism is the use of special radar signals to automatically trigger an IFF transponder in a friendly aircraft "painted" by the radar. A transponder responds,

* in a civilian aircraft, by sending a code identifying it;
* in a military aircraft, by sending, only when detecting a code indicating the radar is part of the friendly-forces' network, a similarly coded signal.


The secondary surveillance radar (SSR) system used in modern air traffic control systems is an outgrowth of the military IFF system used during World War II. The IFF equipment carried by modern military aircraft is compatible with the transponder system used for civilian air traffic control

Another example of transponders is in identification friend or foe systems and air traffic control secondary radar (beacon radar) systems. For general aviation and Commercial aviation transponders used on planes to amplify radar signals making the plane more visible. Most transponders are also able to transmit altitude information and a four digit code known as a transponder code or a "squawk code" to help air traffic controllers in separation.

[spooked911]

6. Yes-- I saw that too, but when I looked up the IFF beacon, all I could

find was that it was another name for the transponder.

In "Crossing the Rubicon", Ruppert seems to think that the IFF beacon is a hijack signal and that flight 11 turning off the beacon meant that it signaled hijack previously. But I don't know where he gets this idea from. I suspect he is wrong because I have not seen any one else say that a hijack signal was activated on any of the flights.

I suppose the IFF beacon could be a separate special transponder, but it seems unlikely to me. The timing difference may simply relate to confusion in different accounts. But I don't know really.

[gbwarming]

7. The IFF reference came from the CNN article, from a DoD timeline

Transponder is the term used for civilian aircraft. They do two basic things - send back a stronger retun pulse to ATC radar and send up to three types of data. Large commercial aircraft will carry transponders capable of all 3 modes.

Mode A - transmits a four digit (octal) code. This is what the pilot sets to identify the airplane according to ATC instructions, or for visual flight rules (not under direct control of ATC) the code 1200. There are a few special codes for emergencies, like 7700.
Mode C - transmits the aircraft altitude. ATC radar, as I understand it, alternates between mode A and C on each sweep.
Mode S - transmits other information - I don't know exactly what, but there is a unique number for each mode S transponder. Most small airplanes do not have this capability.

Military aircraft have IFF transponders. These also have mode A and C (mode A is called mode 3) so that they can operate amongst civilian traffic, but they also have at least one encrpyted mode which will not transmit unless it receives the proper code. You wouldn't want to flying along in your stealth fighter and have an enemy radar trigger a giant (in radar terms) signal that would broadcast your location for hundreds of miles. The CNN article on Paul's timeline is the first place, apparently, that the term IFF was used for Flight 11. I assume this term was used because the speaker was a military person, and not bacause AAL11 actually had a military IFF.

[spooked911]

8. Yes, that makes sense. Thanks.

[meppie-meppie not]

9. sounds like a built in redundancy system to me n/t

[John Doe II]

10. Thanks a lot for the explanation.

:)
Yes, that makes sense.

[MercutioATC]

11. A note about "Mode S":

It broadcasts a unique (by aircraft) code for identification purposes.

ATC systems are not set up to receive this data...it "costs too much".