Jack wrote:

Andrew Gideon wrote:


My recollection of this is that it wasn't a single-use code but a code
that was valid for some window (ie. a day or an hour).

I'll wait for a more detailed explanation from a currently active
professional pilot about the mechanics of this process, which it is
highly unlikely any are about to share on Usenet.

Ah. I'd not thought to search for this until just now...

http://www.washingtonpost.com/ac2/wp...&notFound=true

Since National's reopening last month, flight crews landing at National
have had to provide a secret code to help air traffic controllers verify
that the flight has not been hijacked.

...

Shumann said several planes have been diverted to Dulles since Oct. 4 for
"failures to authenticate."

This is pretty aged, though. I've no idea if the policy is still in place.

- Andrew