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davenicoll

Squawk Zero

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Hi Guys,

 

Just tried to fly some circuits at Gold Coast..Was given a squawk code on the ground and all was going well...

 

I was then instructed to squawk zero,,,Uhhh??...Whan does that mean?

 

Any ideas??

 

Dave

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Posted (edited)

In some countries (i.e. I don't think this is a universally accepted code all around the world) squawking zero is used to indicate that Mode A is not working on your transponder but Mode C is still functional. So in other words you can show up on a radar scope and be interrogated by an ATC radar, but your transponder is unable to send altitude data. I guess an ATC controller might ask you to do that so you stand out on their scope and he/she can then steer everyone else on the scope well clear of you since the controller does not know your altitude and so cannot ensure separation any other way.

The only other time you'd put zero into a transponder as far as I am aware, is when switching from a code with a 7 as the first digit, for example, if you had been assigned the code 7010 by ATC and then they told you to change to 8700, there is a possibility that you might, for a second or two, transitionally select 7700, and that would of course not be good if you then got distracted with something else and forgot mid way through changing the code that you'd left it on 7700 or 7500 or whatever. There have been a few instances where stuff like that has happened and then the authorities have had to scramble fighters to intercept stuff.

An incident where a partial transponder code has caused some confusion, is when an RAF CH-47 Chinook crashed on the Mull of Kintyre in 1994. The incident has still never been fully explained with absolute certainty although it is surmised that the chopper was going a bit too fast at low altitude and flew into clouds and then struck terrain. However, speculation continues to this day because the chopper happened to be carrying some MI5 'spies' and a few other Government people who were involved in that kind of secret intelligence malarkey. What has caused the speculation and conspiracy theories, is that the transponder at the time of impact, was partially tuned to a 'seven code', i.e. if this was done intentionally, it would either mean its radio was out, it was in trouble, or it had been hijacked, but since a complete seven code was never fully input before it crashed, we will never know whether the crew were trying to communicate that something was amiss. So that's one of those instances where if the intent was not to use a seven code, then resetting to zero before tuning the new code might have prevented that speculative mystery.

Edited by Chock
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Alan Bradbury

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14 hours ago, Chock said:

In some countries (i.e. I don't think this is a universally accepted code all around the world) squawking zero is used to indicate that Mode A is not working on your transponder but Mode C is still functional. So in other words you can show up on a radar scope and be interrogated by an ATC radar, but your transponder is unable to send altitude data. I guess an ATC controller might ask you to do that so you stand out on their scope and he/she can then steer everyone else on the scope well clear of you since the controller does not know your altitude and so cannot ensure separation any other way.

Thanks Chock for the helpful information. The author of VOXATC is from the UK so it's possible that this explanation might explain what Dave encountered. Since to my knowledge, this response from VOXATC has never been noted before, I'm leaning more towards it being a deeply buried bug of some sort. VOXATC usually asks to hit the Ident key if it gets confused about transponder stuff. But flying circuits in VOXATC is not the main use of the app, so I guess we'll never know why this happened.

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