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IFF And Transponders  
User currently offlineC172heavy From Canada, joined Aug 2004, 107 posts, RR: 0
Posted (9 years 7 months 2 weeks 5 days 12 hours ago) and read 10552 times:

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?"
8 replies: All unread, jump to last
 
User currently offlineFtrguy From United States of America, joined Aug 2003, 358 posts, RR: 0
Reply 1, posted (9 years 7 months 2 weeks 5 days 12 hours ago) and read 10527 times:

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.

User currently offlineWoodreau From United States of America, joined Sep 2001, 978 posts, RR: 6
Reply 2, posted (9 years 7 months 2 weeks 5 days 11 hours ago) and read 10477 times:

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.
User currently offlineC172heavy From Canada, joined Aug 2004, 107 posts, RR: 0
Reply 3, posted (9 years 7 months 2 weeks 5 days 10 hours ago) and read 10459 times:

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?"
User currently offlineDeltaGuy From , joined Dec 1969, posts, RR:
Reply 4, posted (9 years 7 months 2 weeks 5 days 9 hours ago) and read 10443 times:

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


User currently offlineAAR90 From United States of America, joined Jan 2000, 3451 posts, RR: 47
Reply 5, posted (9 years 7 months 2 weeks 5 days 6 hours ago) and read 10381 times:

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!
User currently offlineLt-AWACS From , joined Dec 1969, posts, RR:
Reply 6, posted (9 years 7 months 2 weeks 5 days 6 hours ago) and read 10380 times:

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

Ciao, and Hook 'em Horns,
Capt-AWACS, Delightfully tacky, yet unrefined


User currently offlineWoodreau From United States of America, joined Sep 2001, 978 posts, RR: 6
Reply 7, posted (9 years 7 months 2 weeks 5 days 1 hour ago) and read 10301 times:

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.
User currently offlinePW4084 From United States of America, joined Mar 2001, 291 posts, RR: 0
Reply 8, posted (9 years 7 months 1 week 6 days 2 hours ago) and read 10226 times:

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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