Transponder code

[Haroon]

Hi

In flight - Entering a different FIR - Controller asks for a squawk change

Do we have to select STBY while changing the code as taught in some books or we can straight away change the code (especially in modern equipment installed in B777 etc)

Someone told me that during a code change it automatically stops and there is no need to put it into standby mode

regards

[Flying Bull]

Hi Haroon,
It all depends ob your type of equipment.
Old school turnknobs - better switch to standby or you might transmit an emergencycode…
New ones - change is normaly possible without standby but its all written down in the appropriate documentation, which should be available to the pilot…

[737aviator]

Actually I've wondered this too although everyone leaves it in TA/RA while changing it and some airports like Stansted say in the jepp brief to set it to 2000 before selecting Standby. From flying school though you got your hand chopped off by an instructor if you tried to change the code before selecting Standby first though.

[italia458]

Do not select standby! ATC will immediately lose you on their screen. You should know your equipment well enough that you don't select an emergency code while switching transponder codes.

This quote is from TC AIM RAC 1.9.1:

ATC radar units are equipped with alarm systems that respond when the aircraft is within radar coverage and the pilot selects the emergency, communication failure or hijack transponder code. It is possible to unintentionally select these codes momentarily when changing the transponder from one code to another. To prevent unnecessary activation of the alarm, pilots should avoid inadvertent selection of 7500, 7600 or 7700 when changing the code if either of the first two digits to be selected is a seven. For example, if it is necessary to change from Code 1700 to Code 7100, first change to Code 1100, then Code 7100, NOT Code 7700 and then Code 7100. Do not select “STANDBY” while changing codes as this will cause the target to be lost on the ATC radar screen.

The only time you select 'standby' is when ATC says "SQUAWK STANDBY" or after landing.

[Spitoon]

The only time you select 'standby' is when ATC says "SQUAWK STANDBY" or after landing.A slightly definitive answer - when it's not quite like that.

As Flying Bull pointed out, it depends on your equipment. But unless it looks like it still relies on valves, it probably won't cause a problem. In the old days it was SOP to go to STBY primarily to avoid setting off alarms on the radar displays but equipment manufacturers - of both transponders and radar processors - soon started building in what are often called 'slugs', slight delays before believing that a changed code really was the next selected code and transponders effectively switched themselves to STBY while code selections changed. In practice it means that a controller using modern kit will not see the new code until the system detects that it's stopped changing.

Just to make things a bit more complicated - not that it changes anything in practice - a modern radar tracker may use inputs from multiple sensors and has all sorts algorithms going on inside the black box to ignore questionable tx'der responses amongst other things.

[FlightPathOBN]

great post Italia! :ok:

[Haroon]

thanks everyone

started building in what are often called 'slugs', slight delays before believing that a changed code really was the next selected code and transponders effectively switched themselves to STBY while code selections changed.

thats what i was interested in.

[italia458]

Spitoon,

In the old days it was SOP to go to STBY primarily to avoid setting off alarms on the radar displays

Pro tip: Don't select an emergency code when changing transponder codes! I promise you that no alarms will go off if you follow that advice. :ok:

Read the last sentence of the quote from TC AIM RAC 1.9.1 I posted above.

[italia458]

Haroon,

Be careful about just believing that your equipment will do what Spitoon said. I talked to an IFR controller and he told me that your XPDR code will indicate when you are switching through numbers, as Spitoon said it would, but he said as soon as you select an emergency code it will show up, there is no delay.

To avoid setting off alarms you need to follow the advice of TC AIM RAC 1.9.1. I will paraphrase it: DO NOT SELECT AN EMERGENCY CODE! It's as simple as that.

[Haroon]

apart from triggering an alarm through an emergency code one can also pass through someone else's code. Dont know how much of a nuisance that can create but perhaps that is also to be avoided as I think I read somewhere.

[italia458]

Haroon,

Don't worry about passing through someone else's code. This isn't rocket-surgery! How on earth are you supposed to know all the other codes that airplanes, being picked up on the same radar screen as you are, would be squawking? And then if you did know them, to move your dials so as not to end up squawking the same code as any other airplane! It's ridiculous!

When ATC says to squawk a code, change to that code immediately and don't select an emergency code. The end.

[Haroon]

its not about "knowing" the codes but "inadvertently" passing through them..

anyway i am not sure if thats an ATC concern or not. i just read it somewhere which i cant remember.

forget about the squawk and please throw some light upon "Rocket-Surgery" is it something like "Brain-Science" :)

[italia458]

Haroon,

its not about "knowing" the codes but "inadvertently" passing through them..


Come on man! It's 2013... we've had transponders for decades. This isn't a problem!

forget about the squawk and please throw some light upon "Rocket-Surgery" is it something like "Brain-Science" :)

It's a combination of rocket science and brain surgery, which means it's double-intense! Very similar to a double-rainbow.

[Haroon]

ok italia thanks a lot

[thermostat]

What I find strange is that after all these years we only have three emergency codes. I think separate codes for engine fire, hydraulic failure, cargo fire, passenger problem, low fuel, smoke in cabin etc etc would be most helpful. Why are humans just like lumps on a log? We need some thinkers among us.

[nitpicker330]

On the Airbus fleets in CX we simply push clear then type in the new code using the numerical keypad.

[bubbers44]

If you don't select 7 as your first code just set it. Keep it simple.

[gorter]

What I find strange is that after all these years we only have three emergency codes. I think separate codes for engine fire, hydraulic failure, cargo fire, passenger problem, low fuel, smoke in cabin etc etc would be most helpful. Why are humans just like lumps on a log? We need some thinkers among us.

Or just keep it simple. Getting more codes would lead to more accidental mis-setting. The three codes are enough to alert ATC to a problem, and how they respond won't really affected by the nature of your situation.

The 3 codes puts a big ring around you and alerts all ATC units that can pick you up on secondary. If ATC then need to start looking up codes then they're more likely to lose their eye off the main issue and that is more likely to lead to a mistake.

[Pub User]

737aviator

some airports like Stansted say in the jepp brief to set it to 2000 before selecting Standby. From flying school though you got your hand chopped off by an instructor if you tried to change the code before selecting Standby first though.

Can I just point out what the UK AIP, ENR 1.6.2.2.1 (e) tell us:

Code 2000. When entering United Kingdom airspace from an adjacent region where the operation of transponders has not been required; or by Mode S transponder equipped aircraft on the aerodrome surface when under tow, or parked and prior to selecting OFF or STDBY - unless otherwise instructed by ATC.

I believe it's something to do with automatically logging-off the Mode S system. Any ATC people here to explain?

[aterpster]

Flying Bull:

Hi Haroon,
It all depends ob your type of equipment.
Old school turnknobs - better switch to standby or you might transmit an emergencycode…
New ones - change is normaly possible without standby but its all written down in the appropriate documentation, which should be available to the pilot…

I started with 64 code transponders then after a few years we went to 4096 with Mode C. The company told us to never go to standby when switching codes. Instead, if assigned a code with a leading "7" use your brain to not select, 7500, 7600, or 7700.

Really not exactly rocket science.

[Spitoon]

on the aerodrome surface when under tow, or parked and prior to selecting OFF or STDBYI 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?! :E

[Capt Claret]

You should know Bloggs, you work there too!:p

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]

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:ok:

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]

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 ;)

[Capn Bloggs]

TCAS uses the transponder system. Transponder off? TCAS inop.
I was a bit flippant there. Here's what the 717 displays:

Transponder Setting/TCAS Status display

STBY / TCAS Off

Alt Off / TCAS Off

Alt On / TCAS STBY

TA / TA ONLY

TA/RA / Nothing

[ATCast]

No problem! ;)

I followed your advice and used the search function and found this marvellous old post (http://www.pprune.org/atc-issues/15022-changing-squack-codes.html#post169220).
Not much has changed in 13 years on pprune. Not the questions, nor your attitude :E

[FlightPathOBN]

From Transport Canada

RAC - 1.0 GENERAL (http://www.tc.gc.ca/eng/civilaviation/publications/tp14371-rac-1-0-474.htm#rac-1-9-2)


"Do not select “STANDBY” while changing codes as this will cause the target to be lost on the ATC radar screen.

Pilots should adjust transponders to “STANDBY” while taxiing for takeoff, to “ON” (or “NORMAL”) as late as practicable before takeoff, and to “STANDBY” or “OFF” as soon as practicable after landing. In practice, transponders should be turned on only upon entering the active runway for departure and turned off as soon as the aircraft exits the runway after landing."

[Capn Bloggs]

And the AIP Australia says...

7.1.9 A pilot operating a Mode S transponder must:
a. Not relevant.

b. On receipt of ATC clearance, or requesting the earlier of Push Back or Taxi, select TA/RA/XPDR/ON AUTO as applicable.

Note 1: If AUTO mode is not available Select ON (e.g. XPDR) and assigned Mode A code.

Note 2: Australia does not require TA/RA to be de--selected while aircraft is on ground.

c. When parked and shutting down engines, select STANDBY.

d. Not relevant.

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 information and possible misidentification of aircraft in automated Australian ATC systems due to temporary selection (while effecting the change) of a code already in use.

:}

[Haroon]

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 information and possible misidentification of aircraft in automated Australian ATC systems due to temporary selection (while effecting the change) of a code already in use.

does anybody know if this applies to any other place apart from Australia

[Capt Claret]

I think the Aussie system is of French design. Should one inadvertently set the wrong TXPR code on the ground in one's Boeing or Airbus, and that code has been assigned to a Cessna 172 on the other side of the country, the automatic pickup once airborne causes all sorts of problems, because the 172 is now exceeding its design perameters and has mysteriously crossed the country. But one's Boeing or Airbus is still safely on the ground. :eek:

[Saratogapp]

How long does it take to change your code? I would think that, immediately you have been instructed to change code (I.e. ATC is EXPECTING a change) going STBY for, say 15 seconds while you dial up the new code and return to AUTO or ALT, is an expectation. What am I missing here?

[Turbavykas]

How long does it take to change your code? I would think that, immediately you have been instructed to change code (I.e. ATC is EXPECTING a change) going STBY for, say 15 seconds while you dial up the new code and return to AUTO or ALT, is an expectation. What am I missing here?

Accidents happen when multiple factors combine. Lets say that there is 1:1000000 chance of engine failure during those 15 seconds. You get multiple warnings, you forget to turn on transponder, you start to descent, nobody know where you are, TA/RA is not working in other aircraft and just happens A380 flying 1000 ft below you. 500 lives lost just for turning transponder to STBY.

[Capt Claret]

Accidents happen when multiple factors combine. Lets say that there is 1:1000000 chance of engine failure during those 15 seconds. You get multiple warnings, you forget to turn on transponder, you start to descent, nobody know where you are, TA/RA is not working in other aircraft and just happens A380 flying 1000 ft below you. 500 lives lost just for turning transponder to STBY.

Not to mention the system chaos as one momentarily selects several different TXPDR codes whilst changing the squark, activating a whol lot of flight plans. :=

[DaveReidUK]

Not to mention the system chaos as one momentarily selects several different TXPDR codes whilst changing the squark, activating a whol lot of flight plans.We were told as far back as post #5 that

equipment manufacturers - of both transponders and radar processors - soon started building in what are often called 'slugs', slight delays before believing that a changed code really was the next selected code and transponders effectively switched themselves to STBY while code selections changedWas that rubbish, then ?

[Haroon]

is there any ATC personnel here reading this post?

[Spitoon]

'equipment manufacturers - of both transponders and radar processors - soon started building in what are often called 'slugs', slight delays before believing that a changed code really was the next selected code and transponders effectively switched themselves to STBY while code selections changed'

Was that rubbish, then ? Not rubbish, but not to be relied upon as universally applicable - there will be old equipment out there and few people using radars will fully understand what processing goes on behind the screens. Just as posts in this thread show that many pilots are not fully aware of how their equipment works.

But as one of my old instructors used to say, it's always a good day when you learn something new.....especially if no one gets killed.

[Natstrackalpha]

A classic tale indeed. Go to Stand-by always. This is a hairy chesnut.

Just go to standby. Then change. Don`t do it any other way.

FOR EXAMPLE. TRUE STORY.

Airliner approaching the US Eastern coast, from the East, like Europe, ok?

Pilot inadvertantly selects a naughty squawk, US ATC kindly invites them to divert.

Pilot argues, it was his error and everything is tickety boo. US ATC, not interested. Divert or else. Pilot diverts. Conclusion: silly pilot.

Standby, before changing squawk, standby before operating from cold. Standby when asked to squawk `standby`
Standby before switching the box off. Standby until airborne for initial squawk.

[Natstrackalpha]

saratogapp. You are missing my post, see further. Also, if you or anyone-else here have not been trained to go through stand by as written, by me, in this thread, then ask for your money back. Also, I don`t care what RAC says if it contradicts what I posted. Whether its RAC from Canada or RAC from IRAQ or WRAC from the Army, or the UK or EASA - you must always change to stand by first.

[Natstrackalpha]

Quote:
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 information and possible misidentification of aircraft in automated Australian ATC systems due to temporary selection (while effecting the change) of a code already in use. does anybody know if this applies to any other place apart from Australia

HAROON You are dead right mate, it applies to the UK as well.

Here is another way of looking at it:


ALWAYS GO TO STAND BY BEFORE CHANGING CODE.

JUST DO IT!!