2 x F-15 using same Hex Code???!!!!!!!

[EGNXR]

Hi all,

Subject says it all. Looks like 2 x F-15 using the same hex at the same time.
Sort of defeats the whole object of mode-s. Serial from a previous confirmed sighting, no guarantee it was one of the frames involved today.

Unless someone has another theory?

Cheers John

[Allocator]

Is this not one F15 (AE06F6 - 91-0329) sending 2 flight ID's at the same time, rather than 2 aircraft using the same hex code?

[DaveReid]

By Murphy's Law, if the USAF keep assigning tactical codes then sooner or later we could well see finger trouble resulting in two aircraft using the same code at the same time.

But in this case, given that the times overlap 100%, I would agree that we're probably looking at a single aircraft.

[viking9]

Military aircraft in formation often have only the leader or a nominated aircraft transponding. Quite safe providing ATC has authorised it.

The GAF (and many others) have been swopping codes for years.

[DaveReid]

The GAF (and many others) have been swopping codes for years.

I disagree.

Changing codes, yes.  Swopping codes, no - if by "swopping" you mean that a code used on one aircraft last week can be used on a different aircraft today.  We've seen little or no evidence of that, and certainly not enough to support the theory.

What's not in doubt is that the Germans (and US, etc) have many more codes available than they have aircraft, and it's becoming increasingly common to see the same aircraft using several different "tactical " codes on different occasions.

But as for the same code being used on different aircraft at different times (discounting aircraft which have been retired), I'm not convinced.  I suppose the proof of the pudding will be when all the available codes have been used once around, then we will see how they start to be reused.

[viking9]

Dave,

Since the F-15s at Lakenheath started to transmit codes a couple of months ago they have been swopping codes. I and other members of spotting groups have confirmed this with Mk 1 eyeballs standing at the perimiter fence. That's why keen mil spotters do not bother logging serials of F-15s that appear on RB or SBS.

As for you seeing no evidence yourself, Dave, you wouldn't if you don't subscribe to sites such as http://live-military-mode-s.eu/ which now only posts the squadron and type for F-15 hex codes.

There is no chance of the USAF running out of codes as they are only swapped between a squadron's own aircraft.

BTW Apache helicopters are equipped with transponders which can have their codes changed remotely, so I'm quite sure the F-15s have that capability.

Tom

[DaveReid]

OK, thanks for the update.

Do you have any specific examples of two airframes which have been recorded using the same code?

Incidentally, do we know whether the F-15 houses its Mode S transponder in a bay on the airframe itself, or in a pod?  And either way, could a box or pod swap account for the same code popping up on different aircraft?

[viking9]

I'm not sure where the transponder is kept but I would imagine it's part of the basic avionics suite in an airframe bay. I assume that the mode s transponder is incorporated into the AN/ALX-76 IFF system but I have no evidence of it. I know a man who could tell me but he said he would then have to kill me :o)

I have no records now of two aircraft using the same code at different times as I removed all serials from my logs once I realised it was happening. The only way to see it again is to spend a couple of days at Lakenheath logging serials again.

Tom

[DaveReid]

I assume that the mode s transponder is incorporated into the AN/ALX-76 IFF system but I have no evidence of it. I know a man who could tell me but he said he would then have to kill me :o)

I think you would have died in vain :-)  Looks like the AN/ALX-76 pre-dates Mode S.

www.f-15estrikeeagle.com/technology/avionics/iff/iff.htm

So we're probably looking at another box somewhere on the aircraft.

[viking9]

I do know the AN-ALX-76 predates mode S, that's why I said "incorporated into". I can see no other 1090 antennae on the ac or pods so mode S must use the original ones. Rather than find space for another LRU on the airframe, associated cabling and somewhere on the instrument panel to fit the controller it would make sense to incorporate a mode S capability into the existing unit and select it from the existing contoller.