NMAC WITH A BIPLANE RPTED BY C182 OBSERVER IN THE REAR SEAT OF A TRAINING FLT N OF SCK; CA.

Narrative

I WAS FLYING IN A C182 ON AN INST TRAINING FLT. I NOTICED A LIGHT COLORED (EITHER WHITE OR YELLOW) BI-WING AIRPLANE PASS IN FRONT OF MY ACFT FROM L TO R. WE WERE ON AN IFR FLT PLAN AT 6000 FT HDG 307 DEGS. I WOULD ESTIMATE THE BI-WING ACFT TO HAVE BEEN HDG APPROX 025-030 DEGS. THE OTHER ACFT PASSED ABOVE US AT WELL LESS THAN 500 FT. WE RECEIVED NO WARNING FROM THE CTLR THAT THERE WAS ANY OTHER ACFT IN OUR VICINITY. THERE WERE 3 PEOPLE ON BOARD MY ACFT -- THE PLT; THE INSTRUCTOR; AND THE PNF IN THE REAR SEAT. THE PF WAS UNDER THE HOOD. AT THE TIME OF THE NMAC; WE WERE UNDER THE CTL OF STOCKTON APCH AND HAD JUST BEEN HANDED OFF TO ANOTHER SECTOR. THE NMAC OCCURRED AFTER THE HDOF AND BEFORE WE HAD A CHANCE TO CONTACT THE NEW CTLR. SINCE THE OTHER ACFT WAS ABOVE US AND COMING FROM A RELATIVE BEARING OF ALMOST 260 DEGS; IT WAS IMPOSSIBLE TO HAVE SEEN HIM. I WOULD ALSO IMAGINE THAT A BI-WING ACFT WOULD HAVE POOR VISIBILITY DIRECTLY AHEAD AND VERY LITTLE VISIBILITY BELOW. IT WOULD APPEAR THAT THIS WAS A SIT THAT EACH PLT DID NOT HAVE ANY CHANCE OF SEEING THE OTHER ACFT. THE BI-WING ACFT FLEW STRAIGHT AHEAD FOR A SHORT PERIOD OF TIME AND THEN STARTED TO TURN. THIS WOULD LEAD ME TO BELIEVE THAT THE OTHER ACFT WAS CONDUCTING SOME TYPE OF VFR MANEUVERS IN THIS AREA. IF THIS ACFT WERE ON A FLT PLAN; THEN IT SHOULD HAVE BEEN AT 7500 FT FOR THE CORRECT HEMISPHERIC ALT. SINCE STOCKTON APCH DIDN'T CALL THE TFC; I WOULD ASSUME THAT THE OTHER ACFT DID NOT HAVE A XPONDER OR IF ONE WAS INSTALLED; IT WAS NOT ON. THIS DID APPEAR TO BE A PRE-1940 TYPE ACFT. AN NMAC RPT WAS FILED.