Transponder code
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 |
Transponder code
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… |
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.
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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. 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. |
great post Italia! :ok:
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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. |
Spitoon,
In the old days it was SOP to go to STBY primarily to avoid setting off alarms on the radar displays Read the last sentence of the quote from TC AIM RAC 1.9.1 I posted above. |
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. |
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.
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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. |
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" :) |
Haroon,
its not about "knowing" the codes but "inadvertently" passing through them.. forget about the squawk and please throw some light upon "Rocket-Surgery" is it something like "Brain-Science" :) |
ok italia thanks a lot
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Transponder
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.
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On the Airbus fleets in CX we simply push clear then type in the new code using the numerical keypad.
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If you don't select 7 as your first code just set it. Keep it simple.
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Originally Posted by thermostat
(Post 7752494)
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.
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. |
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. 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. |
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… Really not exactly rocket science. |
on the aerodrome surface when under tow, or parked and prior to selecting OFF or STDBY |
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. |
939 pages? What sort of an operation down there is it, Claret?! :E
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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. :{ |
Thanks Capt Claret
That's what i was talking about. Now we have to see this regulation for other airspace. |
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. |
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 |
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. |
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. |
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... |
And in other countries you get a new code with each sector! Just shows that there is no single answer.
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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... The discussion here is about the 12 bit Mode A code, not about the ICAO 24 bit address. |
changing codes in-flight??? thats lemming talk. do that in certain Countries, and they will just shoot you down... |
The discussion here is about the 12 bit Mode A code, not about the ICAO 24 bit address. * Some military pilots excepted. |
on arrival at the time of parking it say: "Set Mode A Code 2000 before selecting OFF or STDBY" |
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.
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. |
TCAS uses the transponder system. Transponder off? TCAS inop.
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TCAS uses the transponder system. Transponder off? TCAS inop. 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). 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. |
In B777 if you select STBY then TCAS OFF is displayed in Amber on the ND.
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Spitoon
Is this strictly correct? 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. 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 ;) |
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