From
FAR AIM 4-1-19(e) Transponder Operation (Code Changes):
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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