Transponder ID function inop

[Jan Olieslagers]

I had suspected it since acquiring it, and it has now been confirmed by a kind lady at Brussels information: my KT77 transponder works nice in modes A and C. But when they ask me to ident, I turn the knob to its furthest and non-locking position "TST", and the poor radar operator doesn't see a difference.

Is there something I have misunderstood about how to ident?

Or would there be a defect? I always understood the "ident" is no more or no less than an extra (13th?) bit in the squawk code. I have some soldering skills, enough to connect a cable to a plug (and yes, I know they should be crimped rather than soldered, in aircraft use) and I think I could isolate a defective logic gate in the transponder electronics. What would be my chances of locating the source of trouble? If a defect there is, my suspects are (in order) the switch, cabling, electronics.

I do consider HF-electronics like a less evil variant of black magic, though, and am very reluctant to touch anything on the HF-side.

Or could anyone recommend a decent avionics workshop in Belgium? There's one I've heard of at Zwartberg EBZW, but am afraid they might be expensive, as they mostly work on certified planes (mine isn't).

[mad_jock]

Test is a unit BIT test and has nothing to do with ID.

There is usually a button for ident on the front .

[wigglyamp]

You don't select 'TST' to get the ident function - you push the IDT' button. Which transponder do you have - there isn't a KT77 ? Honeywell's mode S unit is a KT73 and the White ident button is top left. If you have a KT76A mode a/c unit, the ident button is the small red cap below the orange Ident light.

[172driver]

Not sure I've ever flown with this type of transponder, but every one I ever flew with had an 'IDENT' button. Ever thought of hitting that one?

[goldeneaglepilot]

Might be worth taking a picture of the unit in situ - someone on here will recognise it and be able to help

[A and C]

As said above post a photo and someone will be able to help, as for getting it fixed I would sent it it General Aero Services at Thurrock in the UK If it can be fixed Simon at GAS can !

[mad_jock]

Some of the very old Bendixs don't have them.

The 76A was the first I think.

https://dealer.bendixking.com/servle...313-0000_0.pdf

There isn't any manuals on the Bendix site for a KT77. And the only pic I could find of one it didn't look to have one.

[Jan Olieslagers]

Well, it seems I have AGAIN managed to make a fool of myself.
It is clear now that I never properly ident'ed, as I only applied the TST function and that is for something else. Either my transponder has no ident button - but that seems most unlikely - or I managed to completely miss it - much less unlikely.

After some www searching, I believe my transponder must be a King KT78; it certainly has the rectangular orange 'activity' light, (which flickers all the while, in flight and even on the ground) and the four knobs for dialing the squawk code.
Will have to recheck on next visit to aerodome, which is not expected before next weekend.

Thanks to all who responded, and excuse my sillyness!

[mad_jock]

Sometimes the light is the Ident button

Take a photo of the thing and I am sure one of us has used it before.

[goldeneaglepilot]

Have you tried pressing the light's? It's a long time since I used a KT76 or 78, but from memory the ident button is a light under the orange rectangular light you just push in and it illuminates as the ident is activated.

Just found a picture - the KT76 and 78 are in essence the same with different power outputs

[mad_jock]

And BTW the newer transponders are creating even more havok than the old.

I have heard quite a few times now aircraft screwing with ATC radar because there Mode S ident is wrong usually with an exam callsign on it. When asked to change it the pilot doesn't have a clue how to do it.

Which for those that don't know is usually mode 2-3 times until the ident comes up then big knob to move the cursor and small to change it.

[Jan Olieslagers]

GEP: as far as my muddy memory stretches, mine looks even more like in the page mentioned below. But I must really go and photograph it - one week's patience, please.


King KT-78 Transponder - Transponder

[BackPacker]

I have heard quite a few times now aircraft screwing with ATC radar because there Mode S ident is wrong usually with an exam callsign on it.

True. When Mode-S became mandatory in NL there was an initial period when a load of airplanes flew around with wrong flight IDs. Either by accident or on purpose. "JESUS" was apparently the one that made the headlines most prominently.

There was some stern communication from the authorities to all owners/operators, followed by some stern communication from clubs/groups to their members not to mess with the settings (after having verified the settings were correct, of course), and the problem seems to have disappeared now.

What's an "exam callsign" by the way? Is it even allowed to put a flight ID on the transponder other than the aircrafts callsign (e.g. GABCD) or the flight number in case of CAT (e.g. KL8225)?

When asked to change it the pilot doesn't have a clue how to do it.

Depending on the transponder this is actually quite complicated. With the full-width transponder models from, for instance, Garmin, it's doable in-flight if you know what you're doing. But with, for instance, those Trig transponders that fit in an instrument hole, and only have three or four buttons in total it's a complete nightmare. In fact, it's already quite a challenge to put a squawk code (other than 7000) in those, while at the same time keeping a decent lookout.

I agree it's not right, but I don't think ATC should expect pilots to be able to change their flight ID in-flight.

[mad_jock]

Each examinor who is testing at CPL and IR level is given there own call sign examXX. XX being a number. With the CAA chief examinor being EXAM01.

Some schools also with full permission of the authorities issue similar callsigns to thier instructors and the students use them when talking to ATC. When solo they prefix it with student or Solo depending on whats been agreed with the local ATS.

EXAM callsign is meant to mean you have a slightly higher priority than the normal one of zero compared to other light aircraft. And in general the controllers do make life easier for the aircraft.

[goldeneaglepilot]

Jan - slightly different versions of the same unit from the photos. Try pressing the ident light, I'm sure you will find that cures your problem

[BackPacker]

Each examinor who is testing at CPL and IR level is given there own call sign examXX.

Checked the UK AIP. ENR 1.6.2 (SSR procedures):

3.3 In accordance with ICAO Doc 8168 (PANS-OPS) Vol I, Part III, Section 3, Chapter 1, para 1.3, flight crew of aircraft equipped
with Mode S having an Aircraft Identification Feature shall set the Aircraft Identification in the transponder. This setting shall correspond
to the Aircraft Identification specified in item 7 of the ICAO flight plan, or if no flight plan has been filed, the aircraft registration.

Are those exams on a flight plan, with EXAM01 in item 7?

And IF you put it in the transponder, thus changing the default flight ID, should it not be the responsibility of the examiner/examinee to set the transponder back to its normal value (aircraft registration) after the exam? Now this responsibility falls on the unsuspecting next pilot. And I bet checking the flight ID is not part of the default checklist in a lot of places. (In fact, I bet most pilots would not even recognize a mode-S transponder for what it is, let alone be able to verify the Flight ID is correct.)

[mad_jock]

yep they use it for everything and is the defacto flightnumber. Its all offical through the agency that deals with callsigns.

And it really screws with the system apparently when you have two mode S with the same flight ID on apparently.

And quoting PAN -ops and ICAO never works with UK ATC system there are getting on for 9 pages of differences in Jepps. If they published the VFR differences as well it would be bigger than the all the other countrys differences added together.

And its your responsability as PIC to set the aircraft up for your flight what ever the condition it was left in by either the engineers or previous pilot. You should also be current with the operation of the equipement onboard.

[172driver]

it certainly has the rectangular orange 'activity' light, (which flickers all the while, in flight and even on the ground)

FYI, this light tells you your transponder is being interrogated by radar. In a busy radar environment this can mean it's flickering pretty much all of the time.

When pressing the IDENT button it stays on without flickering for a second or so, at least it does on all the units I've ever used.

Now, you may ask, 'why do I need to know that my transponder is being interrogated?' The most important reason IMHO is to warn you of a duff unit. IOW if you are flying in airspace you know is radar controlled and the light stays off, you most likely have a problem - and it's a good idea to communicate with ATC to sort that out. Usually, btw, cycling the transponder does the trick.

[10W]

EXM is the published ICAO code for 'Exam' flights. I would expect to see this, along with the flight number, in the Mode S ID if that is what the pilot is flying as, e.g. EXM01.

[achimha]

yep they use it for everything and is the defacto flightnumber. Its all offical through the agency that deals with callsigns.

Some time ago, my FTO (headed by a Lufthansa captain) decided they want to be an airline and got their own airline flight IDs from whoever issues them. Now instead of using the aircraft's registration (which every student and instructor knows by heart), you have to use the right flight ID from a list. Often, people forget about this and then have to change the flight ID to the aircraft's registration in flight and vice versa.

Most stupid idea ever.