Narrative:

I was approaching 3w3 following the published NOTAM approach procedure for 2 eastern shore, md, GA airports that lay just within the eastern boundary of the dc ADIZ. The procedure calls for aircraft not on a flight plan, and approaching from the east, to follow a defined corridor and squawk a special transponder code: xyzz for 3w3 and xyyw for W29. The 2 GA airports are about 3 mi apart on the coast of the chesapeake bay. An 8 mi wide, east/west ADIZ corridor that overlays route 50 at the annapolis bridge permits this access to both airports. I was specifically following the approach procedure for 3w3 that required an xyzz squawk code. I switched the transponder from 1200 to xyzz prior to penetrating the ADIZ boundary about 10 mi east of the airport at approximately 200 ft MSL. I made a CTAF call on 3w3 airport frequency to announce arrival and check for traffic. There was no immediate response. I continued the approach descending to 1000 ft pattern altitude and after making a second call with no response, I visually determined that there was no traffic in the area, decided to make a pass at pattern altitude upwind to the right of the airfield to check the condition of the grass, the location of the displaced thresholds and the orientation of windsocks. As I neared the field, which is a 2400 ft grass strip and airpark, I got a radio call from someone attending who first said the field was wet and unusable and then said that 'customs' wanted to talk to me. With this information, I decided to complete my pass over the field and then made an immediate right 180 degree turn to exit the ADIZ corridor. I further decided to re-enter the corridor with a plan to land at W29, the nearest airport, to call ATC. We exited the ADIZ and reset the transponder to squawk xyyw per the NOTAM procedure for approaching W29 via the same ADIZ corridor. Upon landing at W29 and exiting the aircraft, I was advised by the attendant there that 'potomac' wanted to speak with me. I called the phone number he gave me and spoke to a controller about the situation. He was familiar with the issue and he advised me that during my approach to 3w3 and within the ADIZ corridor, my transponder abruptly indicated a change from xyzz to 'standard' then back to xyzz. He advised that there would be no further action taken but he recommended that I have the transponder svced. I had explained to him that I did not touch the transponder after the initial change to xyzz squawk during my entire first excursion into the ADIZ corridor. I plan to have the transponder checked. It is an older, rotary knob model that does not get changed from 1200 frequently. There could be dust and debris interfering with the knob contacts.

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Original NASA ASRS Text

Title: PLT OF C172 ARRIVING A 3W3 IN THE DC ADIZ SUFFERS INTERMITTENT XPONDER MALFUNCTION WHICH GENERATES AN OFFICIAL RESPONSE.

Narrative: I WAS APCHING 3W3 FOLLOWING THE PUBLISHED NOTAM APCH PROC FOR 2 EASTERN SHORE, MD, GA ARPTS THAT LAY JUST WITHIN THE EASTERN BOUNDARY OF THE DC ADIZ. THE PROC CALLS FOR ACFT NOT ON A FLT PLAN, AND APCHING FROM THE E, TO FOLLOW A DEFINED CORRIDOR AND SQUAWK A SPECIAL XPONDER CODE: XYZZ FOR 3W3 AND XYYW FOR W29. THE 2 GA ARPTS ARE ABOUT 3 MI APART ON THE COAST OF THE CHESAPEAKE BAY. AN 8 MI WIDE, E/W ADIZ CORRIDOR THAT OVERLAYS RTE 50 AT THE ANNAPOLIS BRIDGE PERMITS THIS ACCESS TO BOTH ARPTS. I WAS SPECIFICALLY FOLLOWING THE APCH PROC FOR 3W3 THAT REQUIRED AN XYZZ SQUAWK CODE. I SWITCHED THE XPONDER FROM 1200 TO XYZZ PRIOR TO PENETRATING THE ADIZ BOUNDARY ABOUT 10 MI E OF THE ARPT AT APPROX 200 FT MSL. I MADE A CTAF CALL ON 3W3 ARPT FREQ TO ANNOUNCE ARR AND CHK FOR TFC. THERE WAS NO IMMEDIATE RESPONSE. I CONTINUED THE APCH DSNDING TO 1000 FT PATTERN ALT AND AFTER MAKING A SECOND CALL WITH NO RESPONSE, I VISUALLY DETERMINED THAT THERE WAS NO TFC IN THE AREA, DECIDED TO MAKE A PASS AT PATTERN ALT UPWIND TO THE R OF THE AIRFIELD TO CHK THE CONDITION OF THE GRASS, THE LOCATION OF THE DISPLACED THRESHOLDS AND THE ORIENTATION OF WINDSOCKS. AS I NEARED THE FIELD, WHICH IS A 2400 FT GRASS STRIP AND AIRPARK, I GOT A RADIO CALL FROM SOMEONE ATTENDING WHO FIRST SAID THE FIELD WAS WET AND UNUSABLE AND THEN SAID THAT 'CUSTOMS' WANTED TO TALK TO ME. WITH THIS INFO, I DECIDED TO COMPLETE MY PASS OVER THE FIELD AND THEN MADE AN IMMEDIATE R 180 DEG TURN TO EXIT THE ADIZ CORRIDOR. I FURTHER DECIDED TO RE-ENTER THE CORRIDOR WITH A PLAN TO LAND AT W29, THE NEAREST ARPT, TO CALL ATC. WE EXITED THE ADIZ AND RESET THE XPONDER TO SQUAWK XYYW PER THE NOTAM PROC FOR APCHING W29 VIA THE SAME ADIZ CORRIDOR. UPON LNDG AT W29 AND EXITING THE ACFT, I WAS ADVISED BY THE ATTENDANT THERE THAT 'POTOMAC' WANTED TO SPEAK WITH ME. I CALLED THE PHONE NUMBER HE GAVE ME AND SPOKE TO A CTLR ABOUT THE SIT. HE WAS FAMILIAR WITH THE ISSUE AND HE ADVISED ME THAT DURING MY APCH TO 3W3 AND WITHIN THE ADIZ CORRIDOR, MY XPONDER ABRUPTLY INDICATED A CHANGE FROM XYZZ TO 'STANDARD' THEN BACK TO XYZZ. HE ADVISED THAT THERE WOULD BE NO FURTHER ACTION TAKEN BUT HE RECOMMENDED THAT I HAVE THE XPONDER SVCED. I HAD EXPLAINED TO HIM THAT I DID NOT TOUCH THE XPONDER AFTER THE INITIAL CHANGE TO XYZZ SQUAWK DURING MY ENTIRE FIRST EXCURSION INTO THE ADIZ CORRIDOR. I PLAN TO HAVE THE XPONDER CHKED. IT IS AN OLDER, ROTARY KNOB MODEL THAT DOES NOT GET CHANGED FROM 1200 FREQUENTLY. THERE COULD BE DUST AND DEBRIS INTERFERING WITH THE KNOB CONTACTS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.