Aerobatic aircraft alleged to have violated class B airspace. Disputed.

Attributes
ACN	309756
Time
Date	199507
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : sfo airport : sjc airport : pao
State Reference	CA
Altitude	msl bound lower : 2500 msl bound upper : 6300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : oak
Operator	general aviation : personal
Make Model Name	Christen (& Pitts) Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	descent other
Flight Plan	None
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 30 flight time total : 390 flight time type : 80
ASRS Report	309756
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	other anomaly other
Independent Detector	other controllera
Resolutory Action	none taken : detected after the fact
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I had been practicing aerobatics near lexington reservoir 30-35 mi southeast of sfo. The aircraft, a pitts special S1A, is based at sjc. Sjc was very busy and I had a hard time raising bay approach to enter sjc's class C airspace when I was finished practicing. I decided to proceed to pao where I landed, and then to proceed to sjc. This would be easier since pao tower would hand me off directly to sjc tower. Before pao cleared me to takeoff, they asked me to phone bay approach after landing. I got back to sjc, parked the airplane in the hangar and called bay. The controller told me that my radar track showed me inside the sfo class B at 6300 ft. There was no disciplinary action, just a warning and a request to be more careful. Playing back the events in my mind, I believe my mode C was incorrect and that I was actually well clear of the class B. I had been practicing aerobatics in the 4000-6500 ft altitude range, finishing off with a lomcevak. I then descended to about 4000 ft over lexington reservoir in preparation for returning to sjc. This was 30 mi from sfo, beyond the lateral limit of the class B. I was certainly not 3000 ft above the nearby mountains. I then flew along the west side of the santa clara valley, descending into pao. When I called up sjc tower, 1 static-filled exchange included 'squawk' and '4600.' I dialed this into the transponder. They called back and said I was squawking my altitude and to squawk XXXX. At this point I was between 2000-2500 ft. I think the transponder and encoder was telling approach that I was at least 2000 ft higher than I actually was and that they thought I was at 4600 ft. Bay had noted no problems when I originally departed sjc. The only explanation I can think of is that the hard aerobatics confused the encoder a bit or that a hand-held radio that came loose from its holder had hit and damaged the encoder. I need to get this checked out. Callback conversation with reporter revealed the following information: reporter states he was at 6000 ft during his aerobatics, then started descending on attempt to return to sjc. He was well below the 4000 ft floor to arriving at pao. He has since flown the aircraft with checks from approach and has received confirmation of his mode C being accurate. Why this isolated misread he does not know.

Original NASA ASRS Text

Title: AEROBATIC ACFT ALLEGED TO HAVE VIOLATED CLASS B AIRSPACE. DISPUTED.

Narrative: I HAD BEEN PRACTICING AEROBATICS NEAR LEXINGTON RESERVOIR 30-35 MI SE OF SFO. THE ACFT, A PITTS SPECIAL S1A, IS BASED AT SJC. SJC WAS VERY BUSY AND I HAD A HARD TIME RAISING BAY APCH TO ENTER SJC'S CLASS C AIRSPACE WHEN I WAS FINISHED PRACTICING. I DECIDED TO PROCEED TO PAO WHERE I LANDED, AND THEN TO PROCEED TO SJC. THIS WOULD BE EASIER SINCE PAO TWR WOULD HAND ME OFF DIRECTLY TO SJC TWR. BEFORE PAO CLRED ME TO TKOF, THEY ASKED ME TO PHONE BAY APCH AFTER LNDG. I GOT BACK TO SJC, PARKED THE AIRPLANE IN THE HANGAR AND CALLED BAY. THE CTLR TOLD ME THAT MY RADAR TRACK SHOWED ME INSIDE THE SFO CLASS B AT 6300 FT. THERE WAS NO DISCIPLINARY ACTION, JUST A WARNING AND A REQUEST TO BE MORE CAREFUL. PLAYING BACK THE EVENTS IN MY MIND, I BELIEVE MY MODE C WAS INCORRECT AND THAT I WAS ACTUALLY WELL CLR OF THE CLASS B. I HAD BEEN PRACTICING AEROBATICS IN THE 4000-6500 FT ALT RANGE, FINISHING OFF WITH A LOMCEVAK. I THEN DSNDED TO ABOUT 4000 FT OVER LEXINGTON RESERVOIR IN PREPARATION FOR RETURNING TO SJC. THIS WAS 30 MI FROM SFO, BEYOND THE LATERAL LIMIT OF THE CLASS B. I WAS CERTAINLY NOT 3000 FT ABOVE THE NEARBY MOUNTAINS. I THEN FLEW ALONG THE W SIDE OF THE SANTA CLARA VALLEY, DSNDING INTO PAO. WHEN I CALLED UP SJC TWR, 1 STATIC-FILLED EXCHANGE INCLUDED 'SQUAWK' AND '4600.' I DIALED THIS INTO THE XPONDER. THEY CALLED BACK AND SAID I WAS SQUAWKING MY ALT AND TO SQUAWK XXXX. AT THIS POINT I WAS BTWN 2000-2500 FT. I THINK THE XPONDER AND ENCODER WAS TELLING APCH THAT I WAS AT LEAST 2000 FT HIGHER THAN I ACTUALLY WAS AND THAT THEY THOUGHT I WAS AT 4600 FT. BAY HAD NOTED NO PROBS WHEN I ORIGINALLY DEPARTED SJC. THE ONLY EXPLANATION I CAN THINK OF IS THAT THE HARD AEROBATICS CONFUSED THE ENCODER A BIT OR THAT A HAND-HELD RADIO THAT CAME LOOSE FROM ITS HOLDER HAD HIT AND DAMAGED THE ENCODER. I NEED TO GET THIS CHKED OUT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES HE WAS AT 6000 FT DURING HIS AEROBATICS, THEN STARTED DSNDING ON ATTEMPT TO RETURN TO SJC. HE WAS WELL BELOW THE 4000 FT FLOOR TO ARRIVING AT PAO. HE HAS SINCE FLOWN THE ACFT WITH CHKS FROM APCH AND HAS RECEIVED CONFIRMATION OF HIS MODE C BEING ACCURATE. WHY THIS ISOLATED MISREAD HE DOES NOT KNOW.

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.