c172heavy
Posts: 105
Joined: Sat Aug 07, 2004 9:39 am

IFF And Transponders

Thu Sep 02, 2004 12:42 am

If I understand this correctly, IFF (Identification, Friend or Foe) is like a transponder for military aircraft, enabling them to identify friendlies on the battlefield. So my question is this: Do military planes use IFF for civil ATC tracking, or do they have separate transponders for this? And if they use IFF, can commercial airliners pick up IFF on TCAS?

Thanks in advance.
"How's that working out for ya?....Bein' clever?"
 
ftrguy
Posts: 347
Joined: Fri Aug 29, 2003 8:17 am

RE: IFF And Transponders

Thu Sep 02, 2004 1:07 am

The IFF is a transponder which is the same thing that is in civilian planes. The "added features" of IFF are not used unless in a wartime situation.
 
Woodreau
Posts: 1182
Joined: Mon Sep 24, 2001 6:44 am

RE: IFF And Transponders

Thu Sep 02, 2004 2:25 am

The civilian transponder has just two modes, well three I guess now...

The civilian modes are: A, C and S
A is the 4 digit octal code that you put in either 1200 or whatever ATC assigns. Mode C is the altitude in hundreds of feet that your transponder encodes. I don't understand how S works, so I won't discuss it, but I believe that's what TCAS uses to handle traffic conflicts. I remember in some other discussion that there was mode B or something like that but it's not used.

The military transponder or IFF has 5 modes: Modes 1, 2, 3/A, 4, and C
Mode 1 is a 2-digit octal code
Mode 2 is a 4-digit octal code
Mode 3/A is a 4-digit octal code where the pilot can put in a squawk if ATC assigns one to the aircraft. This is the same mode that civilian pilots put into their transponder.
Mode 4 is an encrypted code
Mode C is the altitude in hundreds of feet
Mode 4 used to be the primary means of positively id'ing a friendly aircraft because if you had a valid Mode 4 then the only way you could get it was if you had the crypto loaded. But the crypto for Mode 4 has been decertified, so it's still available, but it's not the sole determining factor on determining whether this is a friendly aircraft or ship.
The pilot can't change Modes 1, 2, 4 in the cockpit, but he can turn them off so that he looks like a normal civilian aircraft squawking just modes 3 and C, just like you can turn off your transponder in your cockpit.

The military transponder does respond to TCAS interrogations so when they are doing intercepts, it's in the SOP for the fighters to turn off the Mode C to prevent a TCAS TA/RA with a TCAS equipped aircraft.

Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
c172heavy
Posts: 105
Joined: Sat Aug 07, 2004 9:39 am

RE: IFF And Transponders

Thu Sep 02, 2004 3:25 am

So Mode 1, 2, and 4 would identify military craft on ATC screens, right? But they also have Modes 3/A and C if they want to look like civilian a/c. Why bother having military mode 1, 2, and 4 at all then, couldn't they just use a military-numbered code on 3/A or C mode? I mean if they're not used during an intercept anyways...
"How's that working out for ya?....Bein' clever?"
 
DeltaGuy
Posts: 3965
Joined: Wed Sep 12, 2001 5:25 am

RE: IFF And Transponders

Thu Sep 02, 2004 4:17 am

As I understand it, TCAS is a relatively new thing in military fighters. On the EA-6B, I believe they were putting a standard EVSI in place of the regular analog VSI, so that the aircraft is then TCAS compliant.

When a pilot says he's "squalking parrot", it means he's turning off his transponder, as he's feet dry or flying into enemy airspace..little trivia there.

DeltaGuy
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan
 
AAR90
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Joined: Fri Jan 21, 2000 11:51 am

RE: IFF And Transponders

Thu Sep 02, 2004 7:12 am

So Mode 1, 2, and 4 would identify military craft on ATC screens, right?

None of those are used or seen by civil systems.

But they also have Modes 3/A and C if they want to look like civilian a/c.

Standard civilian transponder code = USA military Mode 3.
Standard civilian transponder altitude reporting = USA military Mode C.

Why bother having military mode 1, 2, and 4 at all then

A whole lot of military tactical uses.  Wink/being sarcastic
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
Lt-AWACS
Posts: 2120
Joined: Mon Jan 14, 2002 2:40 am

RE: IFF And Transponders

Thu Sep 02, 2004 7:14 am

C172- NO modes 1,2 and 4 are not seen by Civilian screens.

Ciao, and Hook 'em Horns,
Capt-AWACS, Delightfully tacky, yet unrefined
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Woodreau
Posts: 1182
Joined: Mon Sep 24, 2001 6:44 am

RE: IFF And Transponders

Thu Sep 02, 2004 11:46 am

When a pilot says he's "squalking parrot", it means he's turning off his transponder

Actually the term is "Strangle parrot" to indicate turning off the transponder or to order aircraft to turn off their transponders.

"Squawk parrot" is along the same lines of the civil ATC use of "Squawk xxxx" or "Squawk altitude"

Parrot is the brevity code for Military Mode 1, 2, 3.

Why bother having military mode 1, 2, and 4 at all then

The interrogator on military radars can pick up all the modes, and you can easily pick out military aircraft from the civilian aircraft. Using modes 1 and 2, you can figure out aircraft unit/mission or if the Mode 1 and 2 are coming from a ship, you can figure out exactly which ship it is (at least the US/NATO ones). For aircraft landing on a carrier, Mode 3 is used to indicate fuel state.


Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
PW4084
Posts: 287
Joined: Tue Mar 06, 2001 7:31 pm

RE: IFF And Transponders

Wed Sep 08, 2004 11:09 am

Since we are on transponders, I thought I'd throw Mode S into the mix. Mode S provides TCAS II ability. Here's a pretty good link:

http://yarchive.net/air/airliners/tcas.html

PW4084

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