"Tom Sixkiller" wrote
Something that's read out over the radio?

Possibly. It could be like the military authentication codes.

Many things are possible, but only one is true. A good friend of mine
is captain for a major airline, has flown in using the procedure, and
told me what actually happens over a beer. Here's how it really is:

It is read out over the radio. In plain english. It's not like an
authentication code. It's a password. One word. Valid for the
entire day. You only get one chance to get it right - get it wrong
and you're sent elsewhere. But all you have to do is listen on
frequency (which is public - it's the standard approach frequency) for
20 minutes or so, and you will know the secret word. It's that
simple, since every airliner uses it on first contact.

Michael