Transponder code

[Spitoon]

on the aerodrome surface when under tow, or parked and prior to selecting OFF or STDBY

I think it's to do with the A-SMGCS - Advanced Surface Movement Guidance and Control System - a development of old ground movement radars. I can't remember all the details but the A-SMGCS tracks aircraft (and sometimes vehicles) with multilateration using mode S. Setting 2000 is something to do with having a target showing up but not tagged with the callsign of another flight.

[Capt Claret]

From JeppView, State Rules & Procedures - Australia, p 939.

7.1.10 Pilots must select the transponder to STANDBY before effecting an SSR code change and returning the transponder to ON/ALT.

NOTE: This action is required to prevent possible loss of displayed aircraft position / label infor-mation and possible misidentification of aircraft in automated Australian ATC systems due to tem-porary selection (while effecting the change) of a code already in use.

[Capn Bloggs]

939 pages? What sort of an operation down there is it, Claret?!

[Capt Claret]

You should know Bloggs, you work there too!

The downside to JeppView manuals is one gets the whole world, can't just get the local manual, and references become very difficult.

[Haroon]

Thanks Capt Claret

That's what i was talking about. Now we have to see this regulation for other airspace.

[Capt Pit Bull]

On modern control heads there is no need to select standby during code changes.

If you are TCAS equipped you most definitely should NOT select standby as you will disable your TCAS. It will have to rebuild its roll call and tracking when you turn your transponder back on. Since you are getting code changes around the same time as RT freq changes and FIR / sector boundaries which are obviously already risk factors, knocking a hole in your TCAS protection is not a good idea.

[Haroon]

Thanks Capt Pit

There's another interesting thing mentioned in Jeppesen EGLL Airport Briefing pages:

on arrival at the time of parking it say: "Set Mode A Code 2000 before selecting OFF or STDBY"

whats the logic behind this?

regards

[Hey Driver]

Turning TCAS off in flight.

I once asked why our company proceedures had changed to leave the transponder on when changing our squawk.
The question was put to me 'What would you prefer to apologise for, squawking the wrong code or bumping into someone?
Unfortunately all the aircraft I have flown require you to select the TCAS off to select STBY.
Turning the TCAS off in flight might not be a good idea.

[RetiredF4]

Go to Stby when leaving CTR to not bother ATC anymore....

......uuups... that was for mil jets only

Otherwise some interesting discussion after more then 40 years an billions of code changes.

[FlightPathOBN]

for me, in working with the transponder codes for ATC/ATM. it is certainly interesting, if not entertaining that it appears that at least in this forum, pilots do not understand their equipment, and the ramifications...

changing codes in-flight???

thats lemming talk. do that in certain Countries, and they will just shoot you down...

[BizJetJock]

And in other countries you get a new code with each sector! Just shows that there is no single answer.

[ATCast]

for me, in working with the transponder codes for ATC/ATM. it is certainly interesting, if not entertaining that it appears that at least in this forum, pilots do not understand their equipment, and the ramifications...

changing codes in-flight???

thats lemming talk. do that in certain Countries, and they will just shoot you down...

Which countries are you referring too?
The discussion here is about the 12 bit Mode A code, not about the ICAO 24 bit address.

[Capn Bloggs]

changing codes in-flight???

thats lemming talk. do that in certain Countries, and they will just shoot you down...

Stop flying your MS over mainland China, FPOBN!

[Spitoon]

The discussion here is about the 12 bit Mode A code, not about the ICAO 24 bit address.

Now seeing a pilot change the 24-bit address in flight would be entertaining*.








* Some military pilots excepted.

[Spitoon]

on arrival at the time of parking it say: "Set Mode A Code 2000 before selecting OFF or STDBY"

See posts #19 and 21.

[Spitoon]

Originally Posted by Capt Pit Bull

If you are TCAS equipped you most definitely should NOT select standby as you will disable your TCAS. It will have to rebuild its roll call and tracking when you turn your transponder back on. Since you are getting code changes around the same time as RT freq changes and FIR / sector boundaries which are obviously already risk factors, knocking a hole in your TCAS protection is not a good idea.

Is this strictly correct?

I thought that if you switch the tx'der to STBY other aircrafts' TCAS would lose your target but your TCAS would continue to track others nearby. Without your tx'der input, I assumed that you would still get TAs on other traffic (but no RAs).

Maybe I've got it all confused somewhere - I've only ever seen it working for real briefly (or only looked at it briefly when I've been up front on a flight) so I'm only going from reading etc.

[Capn Bloggs]

TCAS uses the transponder system. Transponder off? TCAS inop.

[ATCast]

TCAS uses the transponder system. Transponder off? TCAS inop.

Transponder "off" is another condition than transponder "standy".

Standby of a transponder is defined in the Mode S transponder MOPS as:

Standby: Means of selecting the condition in which all transponder functions, other than transmissions on the reply frequency and associated self-testing, are operational (i.e., the Standby condition).

I am not 100% sure how Standby would affect TCAS, because I don't have the TCAS technical documents here with me. Basically TCAS works by interrogating on the interrogation frequency of 1030 MHz and listening to replies on the reply frequency of 1090 MHz.

In Standby mode, a transponder will not reply on 1090 MHz, and therefore it will not be detected by TCAS systems in other aircraft or ATC radar. However, I don't think Standby of a transponder necessarily inhibits transmission on 1030 MHz so your TCAS might still interrogate other aircraft and listen to replies.

[Haroon]

In B777 if you select STBY then TCAS OFF is displayed in Amber on the ND.

[Capt Pit Bull]

Spitoon

Is this strictly correct?

ATCast.

I am not 100% sure how Standby would affect TCAS, because I don't have the TCAS technical documents ..... ,snip>
....., I don't think Standby of a transponder necessarily inhibits transmission on 1030 MHz so your TCAS might still interrogate other aircraft and listen to replies.

I hate to appear brusque, but (a) yes it is correct and (b) tell us what you know, not what you think.

This topic has been covered many times in previous threads. Search facility ftw! It seems I have been answering this question for at least 13 years, and even that answer referenced an earlier thread which is no longer available