Transponder code 7000

SSR

And it does make a positive contrubution to air safety, I used to watch the London air traffic centre screens a lot during my time as a mil assistant. The transponder secondary return is marked as a small cross which is superimposed on the primary return.Due to the masking effects of terrain we would loose primary returns when aircraft operated at lower levels but the SSR return could be seen down to 100 feet. Smaller light aircraft are harder to detect on primary radar especially when they are performing sudden changes of attitude eg aerobatics /thermalling. The primary radar return becomes intermittent but the SSR return is very clear.

So if you have SSR then keep it on !

Thanks very much to you both ! 🙂

The enroute (1.6.2.1) section of the “air pilot” manual explains it all and more here

http://www.ais.org.uk/aes/pubs/aip/pdf/enr/2010602.PDF (free registration)

including all SSR allocations

I’ve attached the file for convenience.

7000 is the standard conspicuity code. You show it by default.

Only when asked by an ATSU will you dial in anything else.

So, say I’m returning home, as usual talking to nobody as I don’t require anything with my transponder set to 7000. But I need to cross the Lakenheath Zone. I give them a yell and the first thing they will give me is a squawk – say 4215. I set that on the transponder, now I show on their screens as 4215.

Once I am in sight of the strip I’ll sign off from them, they’ll then request that I take off ‘their’ code, and replace it with the standard 7000.

Moggy