Narrative:

I departed pao airport for a bay tour. While in san carlos airspace, I requested clearance to enter sfo class B airspace. San carlos gave me the squawk code for transponder. Just after this, san carlos tower told me to change frequency to sfo tower 120.5. I established voice communication with sfo tower, and the tower responded, 'cessna X, squawk XXXX and identify.' I responded, 'squawk XXXX and identify.' my transponder light was on but when I pushed identify, the light did not flash. Sfo tower told me, 'I do not have your transponder.' I told the tower I would recycle the transponder. I did so and the transponder light flashed. She again said she did not have my transponder, and I attempted to recycle again. I was attempting to orient myself on a small body of water outside class B airspace, but while attempting to recycle the transponder, I may have confused that body of water with another in class B airspace. Sfo asked me, 'I have an aircraft in class B at 1500 ft 1 NM southwest. Is that you?' I answered, 'no, I am at 1100 ft west of the field.' sfo responded, 'I see you and you are in class B airspace.' I said, 'ok, ma'am, the transponder is apparently not working and I am turning left to exit class B space and returning to palo alto.' there was no air traffic in my vicinity. Sfo told me to call the tower when I got back. When I returned to palo alto I called sfo tower and talked to sfo supervisor and explained the situation. I have recently finished my IFR rating and am fully aware of the requirement for entering class B airspace. The problem was apparently caused by me misreading visual reference points while attempting to recycle the malfunctioning transponder and by the absence in the aircraft of DME equipment.

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Original NASA ASRS Text

Title: INST RATED PVT PLT IN A C172RG PENETRATED CLASS B AIRSPACE BEFORE OBTAINING CLRNC DUE TO BEING DISTR BY A XPONDER PROB AND CONFUSION AS TO HIS EXACT LOCATION.

Narrative: I DEPARTED PAO ARPT FOR A BAY TOUR. WHILE IN SAN CARLOS AIRSPACE, I REQUESTED CLRNC TO ENTER SFO CLASS B AIRSPACE. SAN CARLOS GAVE ME THE SQUAWK CODE FOR XPONDER. JUST AFTER THIS, SAN CARLOS TWR TOLD ME TO CHANGE FREQ TO SFO TWR 120.5. I ESTABLISHED VOICE COM WITH SFO TWR, AND THE TWR RESPONDED, 'CESSNA X, SQUAWK XXXX AND IDENT.' I RESPONDED, 'SQUAWK XXXX AND IDENT.' MY XPONDER LIGHT WAS ON BUT WHEN I PUSHED IDENT, THE LIGHT DID NOT FLASH. SFO TWR TOLD ME, 'I DO NOT HAVE YOUR XPONDER.' I TOLD THE TWR I WOULD RECYCLE THE XPONDER. I DID SO AND THE XPONDER LIGHT FLASHED. SHE AGAIN SAID SHE DID NOT HAVE MY XPONDER, AND I ATTEMPTED TO RECYCLE AGAIN. I WAS ATTEMPTING TO ORIENT MYSELF ON A SMALL BODY OF WATER OUTSIDE CLASS B AIRSPACE, BUT WHILE ATTEMPTING TO RECYCLE THE XPONDER, I MAY HAVE CONFUSED THAT BODY OF WATER WITH ANOTHER IN CLASS B AIRSPACE. SFO ASKED ME, 'I HAVE AN ACFT IN CLASS B AT 1500 FT 1 NM SW. IS THAT YOU?' I ANSWERED, 'NO, I AM AT 1100 FT W OF THE FIELD.' SFO RESPONDED, 'I SEE YOU AND YOU ARE IN CLASS B AIRSPACE.' I SAID, 'OK, MA'AM, THE XPONDER IS APPARENTLY NOT WORKING AND I AM TURNING L TO EXIT CLASS B SPACE AND RETURNING TO PALO ALTO.' THERE WAS NO AIR TFC IN MY VICINITY. SFO TOLD ME TO CALL THE TWR WHEN I GOT BACK. WHEN I RETURNED TO PALO ALTO I CALLED SFO TWR AND TALKED TO SFO SUPVR AND EXPLAINED THE SIT. I HAVE RECENTLY FINISHED MY IFR RATING AND AM FULLY AWARE OF THE REQUIREMENT FOR ENTERING CLASS B AIRSPACE. THE PROB WAS APPARENTLY CAUSED BY ME MISREADING VISUAL REF POINTS WHILE ATTEMPTING TO RECYCLE THE MALFUNCTIONING XPONDER AND BY THE ABSENCE IN THE ACFT OF DME EQUIP.

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.