COMMUTER ACFT HAS NMAC WITH A VFR LTT.

Narrative

JUST PRIOR TO THE INCIDENT; I THOUGHT I SAW AN INTRUDER TARGET APPROX 2 MI W OF ACR X; AN LTT. MODE C ALT INDICATED 9500 FT; BEING VERY BUSY AT THE TIME AND HAVING OVER 5000 FT SEPARATION; I FELT THEY WOULD NOT BE A FACTOR. I LEARNED OF THE INCIDENT SHORTLY AFTER THAT WHEN ACR X ASKED IF WE KNEW ABOUT THE LTT Y THAT JUST PASSED HIM EBOUND. I TOLD HIM I JUST GOT A TARGET AT HIS 9 O'CLOCK; 3 MI. AT 17100 FT. THE LTT Y CALLED ON FREQ A MIN LATER AND SAID HE CAME PRETTY CLOSE TO AN LTT AND WANTED TO KNOW WHAT HE SHOULD DO. I HAD BOTH PLTS CALL ZOA AND TALK TO A MGR. IT SEEMED THE LTT Y DEPARTED MRY ARPT; SQUAWKING 1200 HE CLBED TO 17500 VFR; HE WAS NOT TALKING TO ANY CTLR AT THE TIME OF INCIDENT. WHEN HE CALLED THE CTR HE EXPLAINED THAT THEY WERE CLBING AT OVER 6000 FPM. WE WERE LUCKY THE EVASIVE ACTION TAKEN BY BOTH PLTS SAVED THEIR LIVES; BUT IT COULD HAVE BEEN EVEN WORSE. THE VICINITY OF THE INCIDENT IS WHERE THE SJC COMMERCIAL JETS ARE DSNDING TO 16000 AND BELOW ON THE ROBIE 1 ARR. THE LTT Y EVASIVE ACTION COULD HAVE BEEN ANOTHER NMAC OR WORSE HAD THEIR BEEN A SJC ARR. I'M SURE THE LTT Y IS AN EXCITING PLANE TO FLY AND I HOPE SOMEDAY TO BE ABLE TO FLY ONE; BUT THE EXTRA MIN IT WOULD TAKE TO REQUEST VFR FLT FOLLOWING; AND ADVISE CTLRS OF YOUR INTENTIONS; WOULD SAVE EVERYONE INVOLVED A LOT OF HEADACHE; AND MAYBE SOME LIVES. ALSO AN ATC COMPUTER THAT CAN TRACK A TARGET CLBING THAT FAST WOULD HELP. UPON FURTHER INVESTIGATION; THE COMPUTER ONLY IDENTED THE TARGET TWICE; ONCE AT 13200 AND ONCE AT 17100 IN HIS CLB. SUPPLEMENTAL INFO FROM ACN 218222. 20 MI SE OF SNS VOR 135 DEG HDG DIRECT GAVIOTA VOR EBOUND TFC AT AT 3 O'CLOCK WAS ON A COLLISION COURSE. I SAID MY CTL TO THE CAPT AND ROLLED THE ACFT INTO A L DSNDING TURN APPROX 30 DEG ROLL AND 7 DEG DOWN PITCH. I WAS ABOUT TO REDUCE PWR BUT THE ACFT JUST WENT OVER TOP OF US AT 100 FT SO THEIR WAS NO NEED.