A C170 SINGLE PLT INADVERTENTLY VIOLATED THE DC ADIZ; AFTER EXCELLENT PREDEP PLANNING; BRIEFING AND PREFLTING.

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PLT PREPARED TO FLY A C170 PURCHASED BY A FRIEND FROM ITS SELLER AT 2W5 (MARYLAND ARPT). THE ARPT IS UNDER THE WASHINGTON; DC; ADIZ; SO HE DOWNLOADED THE DEP PROC FROM PLT WEB SITE. IN ACCORDANCE WITH THIS INFO; HE CALLED THE LEESBURG FSS AND FILED HIS ADIZ PENETRATION FLT PLAN. HE THEN CALLED POTOMAC APCH AND RECEIVED HIS DISCRETE XPONDER CODE AND DEP FREQ. THE ACFT WAS THEN FUELED AND PREFLTED. PLT HAS OVER 900 HRS IN HIS OWN ACFT; A C170; BUT ALL AIRPLANES HAVE VARIOUS ITEMS THAT ARE UNIQUE TO THAT ACFT. THE ACFT THAT PLT WAS RETRIEVING; UNDER PART 91; HAS NARCO RADIOS. THE C170 HE REGULARLY FLIES HAS KING RADIOS. IN ADDITION; THE SWITCH PANEL FOR THE INTERCOM AND HEADSETS; WHICH WERE INSTALLED BY THE PREVIOUS OWNER; WERE NOT WELL MARKED SO THE OWNER BRIEFED THE PLT; AND THE NEW OWNER WHO WAS ACCOMPANYING PLT; TOGETHER. AFTER THE ENG RUN-UP; PLT CONFIRMED THE RADIO FREQS AND DID A RADIO CHK WITH THE FBO ON THE CTAF. UPON DEP; PLT BEGAN TO CLB ON COURSE FOR THE BROOKE VOR; WHICH WAS THE FILED RTE. ONCE HE REACHED 800 FT MSL; PLT ATTEMPTED TO CALL POTOMAC BUT DID NOT RECEIVE A RESPONSE TO HIS CALL. PLT CONTINUED TO CALL; WHEN ABLE; BTWN OTHER TFC XMISSIONS UNTIL HE PASSED THROUGH APPROX 1500 FT. THE CTLR AT POTOMAC WHO PROVIDED THE DISCRETE SQUAWK CODE EARLIER HAD ADVISED PLT THAT POTOMAC SHOULD BE ABLE TO TALK TO PLTS DEPARTING ACFT QUICKLY ONCE IN THE AIR OFF 2W5; MAYBE ONLY AT 400-500 FT MSL. WHEN PLT'S ATTEMPTS TO CONTACT POTOMAC WERE NOT ANSWERED; PLT BECAME VERY CONCERNED THAT HE MAY HAVE A RADIO FAILURE SINCE HE COULD NOT ESTABLISH 2-WAY RADIO CONTACT. THE NEWLY-PURCHASED ACFT HAD ONLY 1 COM RADIO; SO SWITCHING RADIOS WAS NOT AN OPTION. RECOGNIZING THAT HE AND HIS COMPANION WERE IN HIGHLY SENSITIVE AIRSPACE; PLT DETERMINED THAT THE MOST PRUDENT THING TO DO WAS TO TURN BACK IMMEDIATELY AND GET THE ACFT ON THE GND. PLT WAS ONLY 5-6 MI OUT AT THIS TIME AND WAS ABLE TO RETURN QUICKLY. UPON ENTRY INTO THE PATTERN; PLT WAS UNABLE TO RAISE ANYONE ON UNICOM; WHICH HE HAD DONE PREVIOUSLY DURING THE RADIO CHK BEFORE DEP. ONCE ON THE GND; AS PLT TAXIED BACK TO THE FBO; THE NEW OWNER OF THE ACFT BEGAN TO TROUBLESHOOT THE PROB. THE NEW OWNER AND COPLT FOUND THAT ONE OF THE SMALL SWITCHES ON THE INTERCOM PANEL WAS NOT IN THE POS THAT IT SHOULD HAVE BEEN IN. THE PROB WAS RECTIFIED; AND THE ACFT WAS AGAIN ABLE TO XMIT TO THE FBO. PLT SHUT DOWN THE ENG ON THE RAMP AND IMMEDIATELY WENT INTO THE OFFICE AND CALLED POTOMAC. THE LINE WAS BUSY FOR A SHORT TIME; BUT WHEN PLT GOT THROUGH TO POTOMAC; PLT EXPLAINED TO THE CTLR WHAT HAD HAPPENED. THE POTOMAC CTLR STATED; 'OK; I'LL LET THEM KNOW.' PLT ALSO TOLD THE CTLR THAT THE PROB HAD BEEN FIXED; AND THAT PLT WOULD LIKE TO DEPART AGAIN. THE CTLR INDICATED THAT DEP WOULD BE FINE; BUT THAT SINCE PLT HAD 'TANKED UP ON THE SYS; BUT DROPPED OUT;' PLT WOULD NEED TO GO THROUGH THE ENTIRE DEP FILING SEQUENCE ONCE AGAIN. PLT CALLED LEESBURG FSS FOR A NEW ADIZ FLT PLAN. WHEN PLT EXPLAINED WHAT HAD HAPPENED THE FIRST TIME; AS WELL AS PLT'S ACTIONS IN RESPONSE TO THE RADIO DIFFICULTY; THE BRIEFER TOLD PLT THAT PLT HAD DONE THE RIGHT THING. WITH THE NEW FLT PLAN FILED; PLT CALLED POTOMAC AGAIN AND RECEIVED THE NEW DISCRETE XPONDER CODE. ON THE SECOND DEP ATTEMPT; PLT WAITED UNTIL HE WAS APPROX 1000 FT MSL BEFORE MAKING HIS FIRST CALL. AGAIN; HE RECEIVED NO RESPONSE. PLT CALLED AGAIN; AND THIS TIME THE CTLR RESPONDED; 'DO I HEAR '1234X CALLING?' PLT WAS ACTUALLY FLYING '1234Y' AND PLT THOUGHT THAT THE CTLR MIGHT BE TRYING TO REACH PLT; BUT THAT PERHAPS CTLR HAD MISUNDERSTOOD PLT'S XMISSION AND IDENT. THE FREQ WAS VERY BUSY; AND PLT DID NOT WANT TO STEP ON SOMEONE ELSE'S XMISSION. PLT WAITED A SHORT TIME AND NO ONE ANSWERED THE CTLR; SO PLT ASSUMED THAT CTLR WAS CALLING FOR PLT'S '34Y.' PLT ANSWERED WITH 'CESSNA 1234Y CLBING OUT OF MARYLAND 2W5 WITH ADIZ FLT PLAN ON FILE; SQUAWKING XXXX;' AND CTLR RESPONDED WITH '34Y WE SHOW YOU ON COURSE.' LATER CAME A FREQ CHANGE AND THEN RELEASE AS PLT CLRED THE ADIZ BOUNDARY.