Transponder code changes question

[FlyingForFun]

From FAR AIM 4-1-19(e) Transponder Operation (Code Changes) (http://www2.faa.gov/atpubs/AIM/Chap4/aim0401.html#4-1-19):1. When making routine code changes, pilots should avoid inadvertent selection of Codes 7500, 7600 or 7700 thereby causing momentary false alarms at automated ground facilities. For example, when switching from Code 2700 to Code 7200, switch first to 2200 then to 7200, NOT to 7700 and then 7200. This procedure applies to nondiscrete Code 7500 and all discrete codes in the 7600 and 7700 series (i.e. 7600-7677, 7700-7777) which will trigger special indicators in automated facilities. Only nondiscrete Code 7500 will be decoded as the hijack code.Interesting. The bit in bold is the complete opposite of what I've always been led to believe - which is that only the specific codes of 7500, 7600 and 7700 will be shown as emergency codes on your screens.

Is this a difference between the UK and the US, maybe? Or am I just wrong?

Thanks!

FFF
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[5milesbaby]

In the Uk only the codes 7500, 7600, and 7700 will trigger the alerts off, as many of the 76** and 77** codes are normal allocation, for definate 770* is from LHR!!!!!!!!

[Chilli Monster]

I don't see what you're getting at. I admit it's not exactly written in the clearest english (what official document is ;)) but all it's saying is don't go from (for example):

2600 - 7600 - 7610 (which is available as a discrete code somewhere probably). The three 'special' squawks will set the bells and whistles off everywhere. (well - a feeble and annoying electronic 'squeak' where I work :))

To be quite honest this is over-regulation in its purest sense. Use a bit of common sense when you change squawk, don't inadvertantly select an emergency code - it's not difficult. If you're worried about it then play safe and select standby whilst changing.

[FlyingForFun]

5miles - thanks, appears to be a difference between the two countries, in that case.

Chilli - no, that's not how I read it at all. The way I read it is that 76** and 77** are not normal allocation. As you (and 5miles) say, this isn't the way it works in the UK - but according to this link, it is how it works in the US. Which I didn't know before.... but I do now! ;)

FFF
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[Scott Voigt]

Chile Monster;

The AIM is for the most part, not regulatory in the US. It is a recomended operating practice... It's just a free govt. publication ( well sometimes free <G>) that tells pilots how they should operate in the National Airspace System.

regards

Scott H. Voigt

[Wee Weasley Welshman]

I regularly get issued with 7701 on BRS - Alicante sectors, usually early in the morning. One has to be extra careful not to let the newspapers, mugs of tea and bag of doughnuts nudge the selector over the next 2 hours.

WWW

[FlyingForFun]

Scott,

Thanks - didn't know that.

So is the "operating practice" of your radar equipment flagging, for example, 7701, as an emergency squawk actually implemented in the US? Because as WWW says, it's certainly not an emergency code in Europe - but the AIM seems to say "recommend" that it should be in the US!


Oh dear, I was expecting a short yes/no answer - this hardly seems important enough to warrant a whole thread! Thanks anyway!

FFF
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[Chimaera]

I'm an ATCO & PPL.

I was taught from the beginning of my flying training - switch to standby, change code, switch back on.

I thought that was standard practice, and think that those that don't go to standby and risk inadvertantly selecting emergency codes are lazy muppets!:* It's not exactly difficult or time consuming afterall!

[Down...2 greens]

Chimaera,

Selecting STBY before changing squawk is good practice on the transponders generally fitted to light aircraft. However, most units installed on larger types include a feature which automatically suppresses returns for a few seconds when a new selection is made, so this sidesteps the problem without the pilot having to select STBY manually.