Originally Posted by Peetah
Thanks for clearing that up. Did a little more reading (can't they ever print this crap up in mixed case?) and found the procedure, in part 4 of a different NOTAM:
Actually, this NOTAM doesn't apply to operations at DCA. Part 4 only applies to the airports mentioned in part 2:
COLLEGE PARK AIRPORT (CGS); POTOMAC AIRFIELD (VKX);OR WASHINGTON EXECUTIVE/ HYDE FIELD (W32)
Since DCA is closed to general aviation, I presume there's a NOTAM with more specific information that's not published and available to us.
Your original NOTAM is the correct one. Presumably the discreet transponder code is assigned when the flight plan is filed and is not broadcast over the air. Each aircraft will be given its own code in advance, so when the aircraft approaches the Washington ADIZ, ATC will tell the aircraft to squak the code in the flight plan. If they dial in the wrong code, they get sent to IAD. Presumably.