Narrative:

I was en route to half moon bay airport from the southeast along the coast. The airport itself and area to the west was covered with a layer of cloud or fog, tops about 1500 ft MSL, undetermined bottom. No official WX is available for haf. Other than the coastal area, WX was clear and unlimited visibility. I elected to continue in clear VMC at 2000 ft MSL slightly north of the estimated airport location, along the edge of the cloud area. I am reasonably familiar with the area, having been to haf several yrs ago on multiple light aircraft flts. There is often a 'hole' along the coast, while allows a legal descent, and VMC flight to the airport under the cloud layer. The area for this maneuvering is sometimes found just to the north, in sfo class B, sector F. I believed the cloud layer extended only to the coastline, as observed while en route to haf. Accordingly, I followed the edge of the cloud slightly (approximately 3-4 mi) north of the assumed airport location. As I was ready to turn back to the haf area, I saw a small town at my 1-2 O'clock position, which was probably rockaway beach. If so, I may have inadvertently strayed into the sfo class B airspace, sector a, at 1500 ft or 2000 ft MSL. I made an immediate left turn (southwest) away from the area and decided to begin my VFR flight back to my alternate airport, watsonville. I believe that the problem is due to a precise ATC boundary which must not be crossed, but which cannot be precisely determined by the pilot using pilotage methods. Sfo class B is not alone in this circumstance. While I believe that I did not stray into the referenced sector, it is possible that I did. When radar contact was resumed a few moments later with ZOA for flight following to watsonville, I was '7 mi south of sfo airport,' which is well outside the referenced sector a.

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Original NASA ASRS Text

Title: A PIPER PA28 PLT ATTEMPTING TO LOCATE HAF ENTERED SFO CLASS B AIRSPACE WITHOUT CLRNC.

Narrative: I WAS ENRTE TO HALF MOON BAY ARPT FROM THE SE ALONG THE COAST. THE ARPT ITSELF AND AREA TO THE W WAS COVERED WITH A LAYER OF CLOUD OR FOG, TOPS ABOUT 1500 FT MSL, UNDETERMINED BOTTOM. NO OFFICIAL WX IS AVAILABLE FOR HAF. OTHER THAN THE COASTAL AREA, WX WAS CLR AND UNLIMITED VISIBILITY. I ELECTED TO CONTINUE IN CLR VMC AT 2000 FT MSL SLIGHTLY N OF THE ESTIMATED ARPT LOCATION, ALONG THE EDGE OF THE CLOUD AREA. I AM REASONABLY FAMILIAR WITH THE AREA, HAVING BEEN TO HAF SEVERAL YRS AGO ON MULTIPLE LIGHT ACFT FLTS. THERE IS OFTEN A 'HOLE' ALONG THE COAST, WHILE ALLOWS A LEGAL DSCNT, AND VMC FLT TO THE ARPT UNDER THE CLOUD LAYER. THE AREA FOR THIS MANEUVERING IS SOMETIMES FOUND JUST TO THE N, IN SFO CLASS B, SECTOR F. I BELIEVED THE CLOUD LAYER EXTENDED ONLY TO THE COASTLINE, AS OBSERVED WHILE ENRTE TO HAF. ACCORDINGLY, I FOLLOWED THE EDGE OF THE CLOUD SLIGHTLY (APPROX 3-4 MI) N OF THE ASSUMED ARPT LOCATION. AS I WAS READY TO TURN BACK TO THE HAF AREA, I SAW A SMALL TOWN AT MY 1-2 O'CLOCK POS, WHICH WAS PROBABLY ROCKAWAY BEACH. IF SO, I MAY HAVE INADVERTENTLY STRAYED INTO THE SFO CLASS B AIRSPACE, SECTOR A, AT 1500 FT OR 2000 FT MSL. I MADE AN IMMEDIATE L TURN (SW) AWAY FROM THE AREA AND DECIDED TO BEGIN MY VFR FLT BACK TO MY ALTERNATE ARPT, WATSONVILLE. I BELIEVE THAT THE PROB IS DUE TO A PRECISE ATC BOUNDARY WHICH MUST NOT BE CROSSED, BUT WHICH CANNOT BE PRECISELY DETERMINED BY THE PLT USING PILOTAGE METHODS. SFO CLASS B IS NOT ALONE IN THIS CIRCUMSTANCE. WHILE I BELIEVE THAT I DID NOT STRAY INTO THE REFED SECTOR, IT IS POSSIBLE THAT I DID. WHEN RADAR CONTACT WAS RESUMED A FEW MOMENTS LATER WITH ZOA FOR FLT FOLLOWING TO WATSONVILLE, I WAS '7 MI S OF SFO ARPT,' WHICH IS WELL OUTSIDE THE REFED SECTOR A.

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.