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.

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:

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.

great post Italia! :ok:

thanks everyone

thats what i was interested in.

Spitoon,

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.

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.

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,

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

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

ok italia thanks a lot

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.

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

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

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.

737aviator

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

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

Flying Bull:

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.