Narrative:

The report describes a problem that occurred on a flight from crisfield, md (W41) to tipton/fort meade (fme) in my piper cherokee on oct/mon/03. I filed an ADIZ VFR flight plan prior to departing W41, which called for me to enter the ADIZ over easton, md (esn). When I arrived over esn, I contacted potomac TRACON on 126.75 to obtain a squawk code. The ATC told me to squawk xyzw, which I did. I then entered the ADIZ and was under continuous 2-WAY control of potomac approach during my entire flight from esn to fme. On the way, the potomac approach ATC provided alerts to the presence of other aircraft. At approximately XA10 EDT I passed over the drag strip fix on my approach to fme, about 5 mi southeast of the airport. As I neared fme the potomac approach ATC contacted me and I understood him to say 'squawk VFR frequency change approved.' I interpreted this to mean that I should squawk 1200, the VFR code and change my receiver frequency to 123.05, the fme unicom frequency. Since I always do what ATC tells me to do, I changed my squawk code from xyzw to 1200, my radio frequency to fme unicom and then made an uneventful landing at fme. After landing at fme, I was advised by the airport manager to call potomac TRACON which I did immediately. I was informed that I was in violation of the ADIZ NOTAM when I switched the squawk code from xyzw to 1200 prior to landing, as I believed I was instructed by the ATC. I have flown in and out of the ADIZ dozens of times and have never had a violation. I have always followed the instructions of ATC concerning squawk codes. Always in the past, ATC advised me to stay on the assigned squawk code until landing on the runway and I have followed these instructions. However, this time was different because I didn't get this instruction. Rather, I got what I believed to be an instruction to change to the VFR code. As a corrective action, I recommend ATC always emphasize that the assigned squawk code is to be maintained down to the ground and that further ATC instructions be unambiguous and phrased in a way that won't be misconstrued by the pilot. As a pilot, I should always double-check to verify any instructions that seem to be ambiguous before I take action. Also, in the future, I will always stay on the assigned squawk code right down to the ground no matter what I think I heard the ATC say. Finally, I might write this incident off as a case of me misunderstanding or misinterpreting what the ATC said due to the busy cockpit activities and stresses of my approach and landing, except that I talked to the pilot who landed right behind me at fme and he said he also heard the ATC give me the 'squawk VFR frequency change approved' instruction, which he thought strange in light of his understanding of the ADIZ NOTAM.

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Original NASA ASRS Text

Title: PA28 PLT WAS SQUAWKING AN ASSIGNED DISCRETE XPONDER CODE WITHIN DC ADIZ, AND WAS TOLD TO SQUAWK 'VFR' BY THE PCT APCH CTLR WHEN NEARING HIS DEST ARPT, WITHIN DC ADIZ. WHEN HE COMPLIED WITH THE CTLR'S CLRNC, HE WAS VIOLATED FOR NOT SQUAWKING A DISCRETE XPONDER CODE WITHIN DC ADIZ.

Narrative: THE RPT DESCRIBES A PROB THAT OCCURRED ON A FLT FROM CRISFIELD, MD (W41) TO TIPTON/FORT MEADE (FME) IN MY PIPER CHEROKEE ON OCT/MON/03. I FILED AN ADIZ VFR FLT PLAN PRIOR TO DEPARTING W41, WHICH CALLED FOR ME TO ENTER THE ADIZ OVER EASTON, MD (ESN). WHEN I ARRIVED OVER ESN, I CONTACTED POTOMAC TRACON ON 126.75 TO OBTAIN A SQUAWK CODE. THE ATC TOLD ME TO SQUAWK XYZW, WHICH I DID. I THEN ENTERED THE ADIZ AND WAS UNDER CONTINUOUS 2-WAY CTL OF POTOMAC APCH DURING MY ENTIRE FLT FROM ESN TO FME. ON THE WAY, THE POTOMAC APCH ATC PROVIDED ALERTS TO THE PRESENCE OF OTHER ACFT. AT APPROX XA10 EDT I PASSED OVER THE DRAG STRIP FIX ON MY APCH TO FME, ABOUT 5 MI SE OF THE ARPT. AS I NEARED FME THE POTOMAC APCH ATC CONTACTED ME AND I UNDERSTOOD HIM TO SAY 'SQUAWK VFR FREQ CHANGE APPROVED.' I INTERPRETED THIS TO MEAN THAT I SHOULD SQUAWK 1200, THE VFR CODE AND CHANGE MY RECEIVER FREQ TO 123.05, THE FME UNICOM FREQ. SINCE I ALWAYS DO WHAT ATC TELLS ME TO DO, I CHANGED MY SQUAWK CODE FROM XYZW TO 1200, MY RADIO FREQ TO FME UNICOM AND THEN MADE AN UNEVENTFUL LNDG AT FME. AFTER LNDG AT FME, I WAS ADVISED BY THE ARPT MGR TO CALL POTOMAC TRACON WHICH I DID IMMEDIATELY. I WAS INFORMED THAT I WAS IN VIOLATION OF THE ADIZ NOTAM WHEN I SWITCHED THE SQUAWK CODE FROM XYZW TO 1200 PRIOR TO LNDG, AS I BELIEVED I WAS INSTRUCTED BY THE ATC. I HAVE FLOWN IN AND OUT OF THE ADIZ DOZENS OF TIMES AND HAVE NEVER HAD A VIOLATION. I HAVE ALWAYS FOLLOWED THE INSTRUCTIONS OF ATC CONCERNING SQUAWK CODES. ALWAYS IN THE PAST, ATC ADVISED ME TO STAY ON THE ASSIGNED SQUAWK CODE UNTIL LNDG ON THE RWY AND I HAVE FOLLOWED THESE INSTRUCTIONS. HOWEVER, THIS TIME WAS DIFFERENT BECAUSE I DIDN'T GET THIS INSTRUCTION. RATHER, I GOT WHAT I BELIEVED TO BE AN INSTRUCTION TO CHANGE TO THE VFR CODE. AS A CORRECTIVE ACTION, I RECOMMEND ATC ALWAYS EMPHASIZE THAT THE ASSIGNED SQUAWK CODE IS TO BE MAINTAINED DOWN TO THE GND AND THAT FURTHER ATC INSTRUCTIONS BE UNAMBIGUOUS AND PHRASED IN A WAY THAT WON'T BE MISCONSTRUED BY THE PLT. AS A PLT, I SHOULD ALWAYS DOUBLE-CHK TO VERIFY ANY INSTRUCTIONS THAT SEEM TO BE AMBIGUOUS BEFORE I TAKE ACTION. ALSO, IN THE FUTURE, I WILL ALWAYS STAY ON THE ASSIGNED SQUAWK CODE RIGHT DOWN TO THE GND NO MATTER WHAT I THINK I HEARD THE ATC SAY. FINALLY, I MIGHT WRITE THIS INCIDENT OFF AS A CASE OF ME MISUNDERSTANDING OR MISINTERPRETING WHAT THE ATC SAID DUE TO THE BUSY COCKPIT ACTIVITIES AND STRESSES OF MY APCH AND LNDG, EXCEPT THAT I TALKED TO THE PLT WHO LANDED RIGHT BEHIND ME AT FME AND HE SAID HE ALSO HEARD THE ATC GIVE ME THE 'SQUAWK VFR FREQ CHANGE APPROVED' INSTRUCTION, WHICH HE THOUGHT STRANGE IN LIGHT OF HIS UNDERSTANDING OF THE ADIZ NOTAM.

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.