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-   -   Transponder code (https://www.pprune.org/tech-log/510693-transponder-code.html)

Haroon 20th Mar 2013 14:48

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

Flying Bull 20th Mar 2013 15:25

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…

737aviator 20th Mar 2013 15:31

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 20th Mar 2013 16:04

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 20th Mar 2013 16:28


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 20th Mar 2013 16:29

great post Italia! :ok:

Haroon 20th Mar 2013 17:31

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 20th Mar 2013 17:34

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 20th Mar 2013 17:39

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 20th Mar 2013 17:42

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 20th Mar 2013 17:56

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 20th Mar 2013 18:02

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 20th Mar 2013 18:09

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 20th Mar 2013 18:13

ok italia thanks a lot

thermostat 20th Mar 2013 23:35

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.

nitpicker330 21st Mar 2013 00:23

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

bubbers44 21st Mar 2013 00:30

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

gorter 21st Mar 2013 00:41


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.

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 21st Mar 2013 00:50

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 21st Mar 2013 02:09

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.


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