Narrative:

I departed va tech airport (bcb) and contacted roanoke approach to request VFR flight following to lynchburg, va (lyh) at 5500 ft. Was assigned a squawk and idented as 'radar contact,' but told that approach was not receiving my mode C. I confirmed current altitude and offered to cycle transponder power to restore mode C. After several mins, approach reported they still couldn't read mode C, but to 'just let me know when you're level 5500 ft.' I reported level at that time, and was issued a traffic warning. At this point, I was 300 ft above, and approximately 2 mi west of the roanoke class C airspace. The next transmission I received from approach, after several mins and after I was well within the lateral limits of the airspace, was (essentially) 'since you're transitioning class C with no mode C I'm going to have to report you. Please give me your name and home base.' I was absolutely shocked, and my first response was a knee-jerk self defense reaction, claiming I was actually above class C. Of course I know mode C is still required there, and the controller reminded me of this. Wanting to cooperate, I provided the requested information, but also expressed my concern that ATC did not provide any instruction to remain clear, alter course, etc, and that it was my belief he was granting an exclusion, as ATC has the authority/authorized to do. He replied, 'it's ok, we can allow it and often do. We just want your information in case you try to come back often.' I still have no clear idea as to whether or not this controller considered me in violation or not. From my perspective, the controller issued a squawk, acknowledged radar contact, was providing traffic callouts, accepted my routing and altitude, and offered means to comply with intent of mode C -- 'just tell me when you're level at 5500 ft, and tell me of any climbs or dscnts.' no vectors were provided. No request to remain clear. It was, in effect, tacit issuance of an exclusion to the mode C requirement. There is no specific language requirement for granting exclusions of this type. In this case, having established communication and radar contact well in advance, I felt the controller, with clear understanding of my intended route, had ample opportunity to ask me to divert because he couldn't accept me in his airspace with a suddenly-broken mode C. Instead, he allowed me to continue and asked for altitude confirmation in an attempt to circumvent the problem. ATC exclusionary authority/authorized is powerful, but apparently there is no strict guideline to articulating this authority/authorized. In my case, it was very easy to assume that since I was 'in the system' and communicating with ATC, that ATC would articulate their requests. Instead, I feel as though I was invited into an 'entrapment' situation, where ATC, instead of being helpful, began policing. All this may be a result of heightened suspicion resulting from recent terrorist actions. However, if this is the case, I think the role of ATC is being undermined by that suspicion. As an aside -- the eastern roanoke approach controller was very helpful in trying to diagnose the problem with my mode C, trying multiple squawks, etc. Actually turned out mode C was responding intermittently. The plane is undergoing diagnostic maintenance as I write this. I had completed a trip the day before through several radar services, and actually transited roanoke's area that very morning with no troubles. This was a new, unexpected malfunction.

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Original NASA ASRS Text

Title: ROA CTLR ADVISES C172 PLT OF UNAUTHORIED CLASS C AIRSPACE ENTRY.

Narrative: I DEPARTED VA TECH ARPT (BCB) AND CONTACTED ROANOKE APCH TO REQUEST VFR FLT FOLLOWING TO LYNCHBURG, VA (LYH) AT 5500 FT. WAS ASSIGNED A SQUAWK AND IDENTED AS 'RADAR CONTACT,' BUT TOLD THAT APCH WAS NOT RECEIVING MY MODE C. I CONFIRMED CURRENT ALT AND OFFERED TO CYCLE XPONDER PWR TO RESTORE MODE C. AFTER SEVERAL MINS, APCH RPTED THEY STILL COULDN'T READ MODE C, BUT TO 'JUST LET ME KNOW WHEN YOU'RE LEVEL 5500 FT.' I RPTED LEVEL AT THAT TIME, AND WAS ISSUED A TFC WARNING. AT THIS POINT, I WAS 300 FT ABOVE, AND APPROX 2 MI W OF THE ROANOKE CLASS C AIRSPACE. THE NEXT XMISSION I RECEIVED FROM APCH, AFTER SEVERAL MINS AND AFTER I WAS WELL WITHIN THE LATERAL LIMITS OF THE AIRSPACE, WAS (ESSENTIALLY) 'SINCE YOU'RE TRANSITIONING CLASS C WITH NO MODE C I'M GOING TO HAVE TO RPT YOU. PLEASE GIVE ME YOUR NAME AND HOME BASE.' I WAS ABSOLUTELY SHOCKED, AND MY FIRST RESPONSE WAS A KNEE-JERK SELF DEFENSE REACTION, CLAIMING I WAS ACTUALLY ABOVE CLASS C. OF COURSE I KNOW MODE C IS STILL REQUIRED THERE, AND THE CTLR REMINDED ME OF THIS. WANTING TO COOPERATE, I PROVIDED THE REQUESTED INFO, BUT ALSO EXPRESSED MY CONCERN THAT ATC DID NOT PROVIDE ANY INSTRUCTION TO REMAIN CLR, ALTER COURSE, ETC, AND THAT IT WAS MY BELIEF HE WAS GRANTING AN EXCLUSION, AS ATC HAS THE AUTH TO DO. HE REPLIED, 'IT'S OK, WE CAN ALLOW IT AND OFTEN DO. WE JUST WANT YOUR INFO IN CASE YOU TRY TO COME BACK OFTEN.' I STILL HAVE NO CLR IDEA AS TO WHETHER OR NOT THIS CTLR CONSIDERED ME IN VIOLATION OR NOT. FROM MY PERSPECTIVE, THE CTLR ISSUED A SQUAWK, ACKNOWLEDGED RADAR CONTACT, WAS PROVIDING TFC CALLOUTS, ACCEPTED MY ROUTING AND ALT, AND OFFERED MEANS TO COMPLY WITH INTENT OF MODE C -- 'JUST TELL ME WHEN YOU'RE LEVEL AT 5500 FT, AND TELL ME OF ANY CLBS OR DSCNTS.' NO VECTORS WERE PROVIDED. NO REQUEST TO REMAIN CLR. IT WAS, IN EFFECT, TACIT ISSUANCE OF AN EXCLUSION TO THE MODE C REQUIREMENT. THERE IS NO SPECIFIC LANGUAGE REQUIREMENT FOR GRANTING EXCLUSIONS OF THIS TYPE. IN THIS CASE, HAVING ESTABLISHED COM AND RADAR CONTACT WELL IN ADVANCE, I FELT THE CTLR, WITH CLR UNDERSTANDING OF MY INTENDED RTE, HAD AMPLE OPPORTUNITY TO ASK ME TO DIVERT BECAUSE HE COULDN'T ACCEPT ME IN HIS AIRSPACE WITH A SUDDENLY-BROKEN MODE C. INSTEAD, HE ALLOWED ME TO CONTINUE AND ASKED FOR ALT CONFIRMATION IN AN ATTEMPT TO CIRCUMVENT THE PROB. ATC EXCLUSIONARY AUTH IS POWERFUL, BUT APPARENTLY THERE IS NO STRICT GUIDELINE TO ARTICULATING THIS AUTH. IN MY CASE, IT WAS VERY EASY TO ASSUME THAT SINCE I WAS 'IN THE SYS' AND COMMUNICATING WITH ATC, THAT ATC WOULD ARTICULATE THEIR REQUESTS. INSTEAD, I FEEL AS THOUGH I WAS INVITED INTO AN 'ENTRAPMENT' SIT, WHERE ATC, INSTEAD OF BEING HELPFUL, BEGAN POLICING. ALL THIS MAY BE A RESULT OF HEIGHTENED SUSPICION RESULTING FROM RECENT TERRORIST ACTIONS. HOWEVER, IF THIS IS THE CASE, I THINK THE ROLE OF ATC IS BEING UNDERMINED BY THAT SUSPICION. AS AN ASIDE -- THE EASTERN ROANOKE APCH CTLR WAS VERY HELPFUL IN TRYING TO DIAGNOSE THE PROB WITH MY MODE C, TRYING MULTIPLE SQUAWKS, ETC. ACTUALLY TURNED OUT MODE C WAS RESPONDING INTERMITTENTLY. THE PLANE IS UNDERGOING DIAGNOSTIC MAINT AS I WRITE THIS. I HAD COMPLETED A TRIP THE DAY BEFORE THROUGH SEVERAL RADAR SVCS, AND ACTUALLY TRANSITED ROANOKE'S AREA THAT VERY MORNING WITH NO TROUBLES. THIS WAS A NEW, UNEXPECTED MALFUNCTION.

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.