Narrative:

Our aircraft was cleared to modesto and the associated arrival into sfo. The initial clearance was to 17000 ft. The controller called out the cpr light transport traffic at 10 O'clock and 4 mi. We said we had it. Both the pilot and myself (the so) had the light transport Y in sight on a parallel flight path and clearly in sight. After we said the traffic was in sight, oakland ATC reclred us 'to 11000 to pass under the traffic.' the pilot had the speed brakes out partially and was descending at roughly 4000 FPM. The conflict wasn't readily apparent until the actual color of the light transport was apparent. I said 'bank right' at the same time the pilot turned right. I kept the light transport in sight out the left window. When the light transport turned left, his underwing surface gave the illusion of even closer proximity. Because the speed brakes were partially out, our turn rate was greatly magnified as the spoilers assisted in our turn. This resulted in a g-force of approximately 2-2 1/2 G's. I kept the traffic in sight and when I said we were well clear, we leveled at 11000. I made an immediate PA to the passenger. When we switched frequencys to another oakland controller, the light transport was being told he should have been on frequency in his area. (The light transport was operating VFR and not on our frequency when the incident happened). In my opinion, there were 2 major factors that contributed to our role in this incident. The first was the mindset of most pilots who operate on an IFR flight plan. That is when cleared on airway, arrival, etc., we think that a deviation off course will get us in trouble. Hence, a real hesitation to turn away. We were also cleared to 11000 to pass under the traffic, which lured us into thinking a turn wouldn't be necessary. The second factor was our acceptance of parallel traffic into condensed traffic areas with parallel runways. Since we were going into the bay area, it didn't seem unusual to see other traffic that close. We didn't know at the time he wasn't on frequency. Because of his small size, his closure was almost insidious. Only when we could distinguish several features of the plane did we realize he wasn't on a parallel course, but closing and descending at a similar rate.

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Original NASA ASRS Text

Title: NMAC.

Narrative: OUR ACFT WAS CLRED TO MODESTO AND THE ASSOCIATED ARR INTO SFO. THE INITIAL CLRNC WAS TO 17000 FT. THE CTLR CALLED OUT THE CPR LTT TFC AT 10 O'CLOCK AND 4 MI. WE SAID WE HAD IT. BOTH THE PLT AND MYSELF (THE SO) HAD THE LTT Y IN SIGHT ON A PARALLEL FLT PATH AND CLRLY IN SIGHT. AFTER WE SAID THE TFC WAS IN SIGHT, OAKLAND ATC RECLRED US 'TO 11000 TO PASS UNDER THE TFC.' THE PLT HAD THE SPD BRAKES OUT PARTIALLY AND WAS DSNDING AT ROUGHLY 4000 FPM. THE CONFLICT WASN'T READILY APPARENT UNTIL THE ACTUAL COLOR OF THE LTT WAS APPARENT. I SAID 'BANK R' AT THE SAME TIME THE PLT TURNED R. I KEPT THE LTT IN SIGHT OUT THE L WINDOW. WHEN THE LTT TURNED L, HIS UNDERWING SURFACE GAVE THE ILLUSION OF EVEN CLOSER PROX. BECAUSE THE SPD BRAKES WERE PARTIALLY OUT, OUR TURN RATE WAS GREATLY MAGNIFIED AS THE SPOILERS ASSISTED IN OUR TURN. THIS RESULTED IN A G-FORCE OF APPROX 2-2 1/2 G'S. I KEPT THE TFC IN SIGHT AND WHEN I SAID WE WERE WELL CLR, WE LEVELED AT 11000. I MADE AN IMMEDIATE PA TO THE PAX. WHEN WE SWITCHED FREQS TO ANOTHER OAKLAND CTLR, THE LTT WAS BEING TOLD HE SHOULD HAVE BEEN ON FREQ IN HIS AREA. (THE LTT WAS OPERATING VFR AND NOT ON OUR FREQ WHEN THE INCIDENT HAPPENED). IN MY OPINION, THERE WERE 2 MAJOR FACTORS THAT CONTRIBUTED TO OUR ROLE IN THIS INCIDENT. THE FIRST WAS THE MINDSET OF MOST PLTS WHO OPERATE ON AN IFR FLT PLAN. THAT IS WHEN CLRED ON AIRWAY, ARR, ETC., WE THINK THAT A DEV OFF COURSE WILL GET US IN TROUBLE. HENCE, A REAL HESITATION TO TURN AWAY. WE WERE ALSO CLRED TO 11000 TO PASS UNDER THE TFC, WHICH LURED US INTO THINKING A TURN WOULDN'T BE NECESSARY. THE SECOND FACTOR WAS OUR ACCEPTANCE OF PARALLEL TFC INTO CONDENSED TFC AREAS WITH PARALLEL RWYS. SINCE WE WERE GOING INTO THE BAY AREA, IT DIDN'T SEEM UNUSUAL TO SEE OTHER TFC THAT CLOSE. WE DIDN'T KNOW AT THE TIME HE WASN'T ON FREQ. BECAUSE OF HIS SMALL SIZE, HIS CLOSURE WAS ALMOST INSIDIOUS. ONLY WHEN WE COULD DISTINGUISH SEVERAL FEATURES OF THE PLANE DID WE REALIZE HE WASN'T ON A PARALLEL COURSE, BUT CLOSING AND DSNDING AT A SIMILAR RATE.

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.