NEAR OCN VOR; CA; A C172 CONDUCTING INST TRAINING AND A BUSINESS JET MISS EACH OTHER BY LESS THAN 100 FT.

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IT WAS THE SECOND SUNNY DAY (VMC) IN 3 WKS. MYSELF AND A FLT INSTRUCTOR WENT UP (VFR) TO FLY VOR APCHS TO OKB (OCEANSIDE ARPT) AT APPROX XA00Z. WE WERE FLYING A HEADING OF 330 DEGS; ALT 4575 FT MSL (INDICATED). WE HAD JUST DEPARTED CRQ WITH THE CORRECT ALTIMETER SETTING; AND GOT THE NEW ALTIMETER SETTING FOR OKB. I SET THE ALTIMETER TO OKB. WE WERE MONITORING SOCAL FREQ 127.3 AND HAD ATTEMPTED TO CONTACT SOCAL FOR IFR CLRNC TO OKB. THEY DID NOT RESPOND. WE WERE JUST ABOUT TO TRY ANOTHER ATTEMPT; WAITING FOR AN OPPORTUNITY ON THE BUSY FREQ. I HAD A VIEW LIMITING DEVICE ON (FOGGLES). I LOOKED UP AT THE MAGNETIC COMPASS TO SEE A BIZ JET DIRECTLY 11 O'CLOCK POS; IN FRONT OF US; AND SLIGHTLY LOWER. IT WAS FLYING FROM OUR L TO R (HIS W; TO E). MOMENTS LATER; THE OTHER PLT XMITTED TO SOCAL 'WE'D LIKE TO FILE WHEN WE GET IN; WE HAD A NEAR MISS; NOT 50; BUT 25 FT.' ATC RESPONDED MOMENTS LATER WITH 'SORRY; WE READ THE OTHER ACFT AT 4200 FT.' WE CONTINUED TO FLY. WE PICKED UP AN IFR CLRNC TO OKB AND DID 2 VOR-A APCHS TO OKB; THEN LANDED AT CRQ. CONTRIBUTING FACTORS: WE CHKED OUR ALTIMETER; IT WAS SET CORRECTLY TO OKB ALTIMETER SETTING. THERE MAY HAVE BEEN A BAROMETRIC PRESSURE VARIANCE BTWN CRQ/OKB AND OUR POS; OR OUR XPONDER MAY HAVE BEEN INCORRECT. I WAS WEARING VIEW RESTRICTING GOGGLES. THE OTHER PLANE MAY HAVE BEEN DSNDING AND WAS IN THE INSTRUCTOR'S BLIND SPOT AND EITHER BECAUSE OF MY HEAD ON HIGH WING; WE DID NOT SEE IT UNTIL IT WAS AT OUR 11 O'CLOCK POS. HE MUST HAVE ALTERED HIS COURSE BY DIVING BELOW US. WE MISSED EACH OTHER BY ONLY A SMALL DISTANCE. I (WE) DETERMINED THAT THE INCIDENT WAS CAUSED BY AT LEAST 3 FACTORS: A) ATC BEING OVERWHELMED BY A LARGE VOLUME OF ACFT. B) VARIANCE BTWN INDICATED ALT ON AN ALTIMETER; AND ACTUAL PRESSURE ALT BEING RPTED BY A XPONDER TO ATC. C) THE OTHER PLT SAW US AT THE MOMENT BEFORE HE PROBABLY ALTERED HIS COURSE BUT NOT IN TIME TO MAINTAIN 500 FT OF CLRNC. WE DID NOT SEE HIM UNTIL HE WAS DIRECTLY (11 O'CLOCK POS) IN FRONT OF US. I WAS NOT ABLE NOR RESPONSIBLE TOMFOR LOOKING OUTSIDE THE COCKPIT. THE FLT INSTRUCTOR WAS; BUT HE COULD NOT HAVE SEEN THIS TFC DUE TO IT BEING IN HIS BLIND SPOT. IT SEEMS THAT WE DID EVERYTHING CORRECTLY. THE OTHER PLT TOO. ATC WAS OVERWHELMED AND DID ITS BEST; BUT A NEAR MISS OCCURRED.