Squawk "Alpha"
 

Occasionally I hear clearances at major European hubs instructing "Squawk Alpha ****". Now I know they don't mean it, if you launched into airways with mode A only they'd get terribly agitated, so WTF do they ask you to do it?

This seems a curious contrast to UK low level radar coverage (in the open FIR) where they are punctilious about asking for "Squawk mode Charlie ****"

Answers on a postcard please...

Mode "Alpha" (or mode alpha with mode charlie) is a CIVIL mode for use with civil aircraft.

Waiting to be struck down with fire here, but is alpha the ident code, whereas charlie just implies the addition of altitude to the info transmitted by the Xponder? As in, when you squawk Mode Charlie, you're actually squawking Mode A/C - thus both ATCOs are technically correct.

RS.

When transponders were first generally introduced they were civil variants of the military IFF. The encoding of the squawk information allowed for (I think) three basic modes A,B, and C. Mode A was for civil use and modes B and C were for military use to allow air defence radar sites to have hopefully positive id on military a/c. In time Mode A has become the standard and the terminology has assumed in the civil world that this is the only one used. Mode C for altitude reporting arrived a lot later.

Not quite right Supermunk. Military IFF comes in Modes 1, 2, 3, 4 (and maybe 5 now?). Mode 3 is the same as Mode A and you may hear military controllers say 'squawk mode 3/A ****'. As someone else suggested Mode C came along a lot later as a bolt-on-goodie to mode A and so controllers may ask for mode A but really want mode C as well.