From your AV site........
Ailing Transponder? Then Get Outta D.C.
When the transponder malfunctioned on a King Air inbound to Ronald Reagan Washington National Airport recently, it sparked a panicked evacuation of the Capitol building ... despite the fact that ATC was fully aware of the aircraft and the pilots had complied with all the protocols. So, to prevent future such unsavory scenes, ATC has changed the protocol. In a NOTAM, the FAA said that effective immediately, anyone flying in the D.C. Air Defense Identification Zone (ADIZ) who finds their transponder is not doing its job must immediately exit the ADIZ by the shortest, most direct course. Further, any pilot who knows the transponder cannot comply with the ATC requirement to continuously transmit had best stay out of the ADIZ altogether. The only exception is if human life is at stake, and the pilot (upon request) will be required to provide justification of such at the completion of the flight.
http://www.avweb.com/eletter/archives/avflash/255-full.html#187529
What happens if you don't know that your transponder isn't working?....scary stuff.