Transponder Types

[robinpiper]

I fly quite a few aircraft all of the same type but with different transponders. How can tell what mode type they are? They dont have written on the front of them this is a mode X type transponder. Most are the simple ones you just dial up the code and switch to on. Can you be seen by TCAS equiped traffic with these types?

One of the aircraft has been upgraded, small and round switch it on and the screen digitally showns 7000 and FL, what type is this?

Should really ask somebody at the flying club but I only usually fly locally VFR

[Rod1]

All the transponders you are using are mode C.

If it was mode a you would have a placard saying no altitude data.

Mode s would be new!

Rod1

[Fuji Abound]

.. .. .. but dont forget you will need to switch on "alt" if you wish to give this information. :)

[B2N2]

If it only has and on/off switch...mode A only (code but no altitude)
Switch with on/off/alt..........mode C (code and altitude)
Switch with on/off/alt/ID (or FLIGHT ID) Mode S...
which means it also has a data link capability.
With the right equipment you can receive traffic info from ATC like with a TIS system:

http://www.aopa.org/whatsnew/air_traffic/tis.html

[Rod1]

BN2N is incorrect, almost all transponders have an ALT position, but this setting will not work unless an altitude encode is added. Hence the mandatory placard saying “no altitude data”. If you select ALT on a transponder with no encode it carries on emitting mode A only.

Rod1

[B2N2]

Ok Ok excuse me very much...is it unreasonable to expect a transponder with ALT knob to have a blind encoder attached( or encoding altimeter) ?
Well, maybe in the UK it is...:E

[Rod1]

is it unreasonable to expect a transponder with ALT knob to have a blind encoder attached

It is very common in the UK to have this arangment, no idea about the US.

Rod1

[Fuji Abound]

B2N2

No flight ID on my Garmin mode S :)

No flight ID on G1000 either :)

Of course on many mode S boxes the PA is also displayed so you know exactly what the enconder is reporting.

[denhamflyer]

FYI

G1000 does have mode S flight ID. max 7 characters entered in the PFD using the TMR/REF key and can be set to SAME AS TAIL, CONFIG ENTRY or PFD ENTRY (installation settings). The first two are automatic and the later can be set each time by the pilot.

This can be changed thru the maintenance settings.

[robinpiper]

So this new computer/digital transponder they have installed may not be in fact be mode S. But I'm still wise to select 7000 and switch them all on when flying VFR

[rustle]

FYI

G1000 does have mode S flight ID. max 7 characters entered in the PFD using the TMR/REF key and can be set to SAME AS TAIL, CONFIG ENTRY or PFD ENTRY (installation settings). The first two are automatic and the later can be set each time by the pilot.

This can be changed thru the maintenance settings.

I think he meant there's no Flight ID button or selection to make in order to squawk it. Certainly true of the Garmin Mode-S transponder.

[bookworm]

I fly quite a few aircraft all of the same type but with different transponders. How can tell what mode type they are? They dont have written on the front of them this is a mode X type transponder. Most are the simple ones you just dial up the code and switch to on. Can you be seen by TCAS equiped traffic with these types?

The practical advice that you have been given above is good. There's a technical aspect that I'll point out and you can subsequently ignore.

SSR interrogations from ground stations come in two Modes, A and C. Mode A says "Send back your 4-digit squawk" and Mode C says "Send back your altitude". Virtually all modern transponders reply to both modes of interrogation. Those without an altitude encoder attached send a null reply to Mode C interrogations.

TCAS sends only Mode C interrogations. It will, however, see replies from transponders without altitude encoding, it just won't know what level they're at, because the response is null.

Thus although transponders without altitude encoding are commonly called "Mode-A transponders", at least by pilots, most of them do in fact respond to Mode C.

[denhamflyer]

You dont need to press a button to send the flight id, it is collected by the SSR in the Mode S Elementary Surveillance (ELS), as is the 24 bit unique address.

I would be surpised if the standard models did not support this since this is whate EUROCONTROL are after. I suspect they are probably sending the reg of the plane by default - but thats a guess, since its one of the standard installation modes. Does anyone know what the installers set for GA?

The GTX33 and 330 support the Flight ID.

[IO540]

What the installer is supposed to set for the 24-bit code is the Mode S code allocated by the national registration authority.

For example the CAA has allocated a Mode S code for every G-reg aircraft; you can see these in the G-INFO database. The FAA has done likewise.

There is an algorithm for converting these 24-bit codes back into the tail number. It is a while since I saw the details but I recall that the encoding of the tail number into the 24-bit integer is done slightly differently for each country. Some of it is quite obscure; unsuprising since 24 bits doesn't allow a straight encoding of anything up to six alphanumeric characters.

One puzzle is whether ATC will ever have live access to the Mode S derived tail number.

Currently, the ATC doing IFR sectors sees a tail number (e.g. N1234X) next to each secondary return blip but this doesn't come from the Mode S return code; it comes from the returned 4-digit Mode A/C squawk which is used as an index into their current IFR flight plan database which obviously contains the tail numbers. I did a visit to W Drayton recently and this is how it works, even if Mode S is available (which it isn't for the most part and won't be for years).

ATC doing LARS sees even less; I vaguely recall (from another ATC visit) that they don't see the tail number next to the blip and have to refer to the appropriate piece of wood which will have the tail number and the squawk written on it. Also, LARS units will be the last to get Mode S, if ever.

Getting back to who is supposed to set the code, I have it on excellent authority that there are clashes, resulting from multiple planes carrying the same Mode S code. These have been witnessed by people using the ground-based Mode S receivers. It's also trivial to change this code, by going into the transponder maintenance pages, and it will be trivial to set it to something carried by another plane of the same type (by looking it up in the public databases) much as, I gather, people already do in droves when using faked number plates on cars to avoid the London congestion charge. It's going to be awfully hard to nick somebody for busting CAS, purely on the basis of a Mode S code. In the absence of a confession they will need radar tapes as well, in other words exactly like they do at present...

Getting back to the conspiracy theory about enroute charges, the radar coverage isn't available at the low level at which most UK GA flies, say 1500ft and below. There are huge gaps and the radar cover required would be massively expensive. It's certainly true that the UK is covered with radar coverage much of which is not available as a service to GA, or to any other civilian traffic, and it's also true that the coverage of secondary radar (if you don't care about having a primary return as well) is much better than the coverage of the primary radar, but this still leaves huge gaps which would make a mockery of any attempt to run enroute charges on this basis. If we are to get universal charges it would most likely be done on the Canadian model where every GA plane pays something like £50/quarter or whatever.

[denhamflyer]

Interesting - I wasnt refering to the 24 bit code but the Flight ID (another 7 characters) - the installer can default this to the reg of the airplane , but this can of course be set to anything under pilot control. In Aus they had great problems with incorrect settings until they got the "pilots trained".

Edit: "The Aircraft Identification transmission must correspond with the aircraft identification specified in item 7 of the ICAO flight plan, or, when no flight plan has been filed, the aircraft registration." extracted from EUROCONTROL Web site - so in the absence of any setting we should be sending our reg! (this is also know as the Flight ID)

It would make sense for the reg to be the default flight ID for GA traffic. They can track who we are anyway - but I would pref that they can address me on the radio directly even if I havent gone thru the squawk setting process yet. (Cant think of an instance that it would have helped - but just like the fact that they could differentiate quickly and address the correct people).
Very worrying that the 24bit code can be overwritten! As for the conspiracy theory I always find it amusing :{ ( as you point out with number plates) that the average nice guy is actually the one that carries the can, but the guy they need to track can avoid it with ease!
They already have access to the tail number via the G-INFO site. Just enter the hex code - now I dont think it would take a genius to automate the web site post and auto tag the radar!
It also strikes me that using mode S properly they would not need to use sqawks codes - simplifying the radio procedures.