Narrative:

I contacted pao tower about 7 DME southwest of osi VOR. Was told to report osi. Level at 3800' MSL, approximately 120 KIAS. Scanning for traffic I saw a high wing, single engine aircraft about my 7-8 O'clock position on a converging course. The aircraft appeared to be slightly beneath me. I thought he might be climbing and pulled up very sharply. I may have penetrated the TCA at 4000', I am not sure. I descended to 3800', reported osi and proceeded to land at pao. I reported the incident to pao ground controller after landing at pao. The major factor here is the very limited amount of airspace in the vicinity of osi and the large amount of VFR traffic. It is necessary to get a good deal of altitude to cross this ridge due to turbulence. The absolute minimum altitude I would want to cross over is 3000'. I usually do it at 3500-3800', just beneath the floor of the sfo TCA at 4000'. This area is like the neck of a funnel. You see everything from small aircraft's to military aircraft going through here. The floor of the TCA here needs to be raised to about 6000', allowing traffic to cross osi at 4500 or 5500'. I had an near midair collision incident about 2 weeks before where an aircraft passed within 500' to my left, head-on, while I was crossing osi for a landing at pao. I did not report that one. Contributing factor is the high wing, low wing visibility problem--hard for aircraft to see traffic slightly above him and hard for me to see traffic below due to wing blocking. Somebody is going to get killed in this are around osi-pao-sql if something is not done to fix this funnel situation.

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Original NASA ASRS Text

Title: SMA PLT TOOK EVASIVE ACTION TO AVOID ANOTHER ACFT, MAY HAVE PENETRATION TCA.

Narrative: I CONTACTED PAO TWR ABOUT 7 DME SW OF OSI VOR. WAS TOLD TO RPT OSI. LEVEL AT 3800' MSL, APPROX 120 KIAS. SCANNING FOR TFC I SAW A HIGH WING, SINGLE ENG ACFT ABOUT MY 7-8 O'CLOCK POS ON A CONVERGING COURSE. THE ACFT APPEARED TO BE SLIGHTLY BENEATH ME. I THOUGHT HE MIGHT BE CLBING AND PULLED UP VERY SHARPLY. I MAY HAVE PENETRATED THE TCA AT 4000', I AM NOT SURE. I DSNDED TO 3800', RPTED OSI AND PROCEEDED TO LAND AT PAO. I RPTED THE INCIDENT TO PAO GND CTLR AFTER LNDG AT PAO. THE MAJOR FACTOR HERE IS THE VERY LIMITED AMOUNT OF AIRSPACE IN THE VICINITY OF OSI AND THE LARGE AMOUNT OF VFR TFC. IT IS NECESSARY TO GET A GOOD DEAL OF ALT TO CROSS THIS RIDGE DUE TO TURB. THE ABSOLUTE MINIMUM ALT I WOULD WANT TO CROSS OVER IS 3000'. I USUALLY DO IT AT 3500-3800', JUST BENEATH THE FLOOR OF THE SFO TCA AT 4000'. THIS AREA IS LIKE THE NECK OF A FUNNEL. YOU SEE EVERYTHING FROM SMA'S TO MIL ACFT GOING THROUGH HERE. THE FLOOR OF THE TCA HERE NEEDS TO BE RAISED TO ABOUT 6000', ALLOWING TFC TO CROSS OSI AT 4500 OR 5500'. I HAD AN NMAC INCIDENT ABOUT 2 WKS BEFORE WHERE AN ACFT PASSED WITHIN 500' TO MY LEFT, HEAD-ON, WHILE I WAS XING OSI FOR A LNDG AT PAO. I DID NOT RPT THAT ONE. CONTRIBUTING FACTOR IS THE HIGH WING, LOW WING VISIBILITY PROB--HARD FOR ACFT TO SEE TFC SLIGHTLY ABOVE HIM AND HARD FOR ME TO SEE TFC BELOW DUE TO WING BLOCKING. SOMEBODY IS GOING TO GET KILLED IN THIS ARE AROUND OSI-PAO-SQL IF SOMETHING IS NOT DONE TO FIX THIS FUNNEL SITUATION.

Data retrieved from NASA's ASRS site as of August 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.