Narrative:

We were flying the wraps 5 arrival to smf, approximately 6 mi southeast of sac descending at 1000 FPM and 280 KTS from 11000 to 10000 ft. A short time prior to this, ATC had called out traffic to us, an small aircraft, which we idented and saw pass off our right side. We were now working with sac approach. The autoplt and automatic throttle were engaged, I was the PF and I was descending in vertical speed mode to 10000 ft. The first officer first spotted the target at our 12 O'clock level position (I estimate that the traffic, an small transport, nwbound, was 1000-2000 ft ahead, centered at the lower edge of the forward windshield). When I first saw the target I couldn't determine if we were head on or overtaking the traffic. I detected no lateral movement in the target. I hesitated to see which way the traffic would turn to avoid us -- if at all. The traffic did not turn, it became apparent that we were closing from his 6 O'clock position (rate of closure was approximately 1000 KTS). I disconnected the autoplt and increased the rate of descent while simultaneously banking off to the right. We passed below and to the right of the small transport. I estimate that the vertical separation was 100-200 ft, and the horizontal separation was less than 300 ft. We leveled off at 1000 ft. After the incident we called sac approach to report the encounter. Approach said he did not have any other target on the radar screen until we were 'right on top of him.' after we had passed the small transport, I believe approach said that he had a mode C readout of 10500 ft on a VFR target. Even in the wide open skies over sacramento, traffic converges (as usual) at the VOR. I would certainly like to know why approach was unable to call this 12 O'clock traffic to us, there was very little other IFR traffic on our frequency. 1 additional point: we were level at 11000 ft for several mins prior to receiving our descent clearance to 10000 ft. I believe that the small transport which was then at our 12 O'clock low position was most likely obscured by our nose until we initiated our descent to 10000 ft. TCASII was not operational on this aircraft (I certainly wish it was). The see and avoid concept has many shortcomings. Fortunately it worked in this case for us, but not by much! This entire event just serves to reinforce in me the absolute necessity to remain largely outside the cockpit in VMC.

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Original NASA ASRS Text

Title: ACR HAS NMAC WITH SMT ON DSCNT. EVASIVE ACTION.

Narrative: WE WERE FLYING THE WRAPS 5 ARR TO SMF, APPROX 6 MI SE OF SAC DSNDING AT 1000 FPM AND 280 KTS FROM 11000 TO 10000 FT. A SHORT TIME PRIOR TO THIS, ATC HAD CALLED OUT TFC TO US, AN SMA, WHICH WE IDENTED AND SAW PASS OFF OUR R SIDE. WE WERE NOW WORKING WITH SAC APCH. THE AUTOPLT AND AUTO THROTTLE WERE ENGAGED, I WAS THE PF AND I WAS DSNDING IN VERT SPD MODE TO 10000 FT. THE FO FIRST SPOTTED THE TARGET AT OUR 12 O'CLOCK LEVEL POS (I ESTIMATE THAT THE TFC, AN SMT, NWBOUND, WAS 1000-2000 FT AHEAD, CENTERED AT THE LOWER EDGE OF THE FORWARD WINDSHIELD). WHEN I FIRST SAW THE TARGET I COULDN'T DETERMINE IF WE WERE HEAD ON OR OVERTAKING THE TFC. I DETECTED NO LATERAL MOVEMENT IN THE TARGET. I HESITATED TO SEE WHICH WAY THE TFC WOULD TURN TO AVOID US -- IF AT ALL. THE TFC DID NOT TURN, IT BECAME APPARENT THAT WE WERE CLOSING FROM HIS 6 O'CLOCK POS (RATE OF CLOSURE WAS APPROX 1000 KTS). I DISCONNECTED THE AUTOPLT AND INCREASED THE RATE OF DSCNT WHILE SIMULTANEOUSLY BANKING OFF TO THE R. WE PASSED BELOW AND TO THE R OF THE SMT. I ESTIMATE THAT THE VERT SEPARATION WAS 100-200 FT, AND THE HORIZ SEPARATION WAS LESS THAN 300 FT. WE LEVELED OFF AT 1000 FT. AFTER THE INCIDENT WE CALLED SAC APCH TO RPT THE ENCOUNTER. APCH SAID HE DID NOT HAVE ANY OTHER TARGET ON THE RADAR SCREEN UNTIL WE WERE 'RIGHT ON TOP OF HIM.' AFTER WE HAD PASSED THE SMT, I BELIEVE APCH SAID THAT HE HAD A MODE C READOUT OF 10500 FT ON A VFR TARGET. EVEN IN THE WIDE OPEN SKIES OVER SACRAMENTO, TFC CONVERGES (AS USUAL) AT THE VOR. I WOULD CERTAINLY LIKE TO KNOW WHY APCH WAS UNABLE TO CALL THIS 12 O'CLOCK TFC TO US, THERE WAS VERY LITTLE OTHER IFR TFC ON OUR FREQ. 1 ADDITIONAL POINT: WE WERE LEVEL AT 11000 FT FOR SEVERAL MINS PRIOR TO RECEIVING OUR DSCNT CLRNC TO 10000 FT. I BELIEVE THAT THE SMT WHICH WAS THEN AT OUR 12 O'CLOCK LOW POS WAS MOST LIKELY OBSCURED BY OUR NOSE UNTIL WE INITIATED OUR DSCNT TO 10000 FT. TCASII WAS NOT OPERATIONAL ON THIS ACFT (I CERTAINLY WISH IT WAS). THE SEE AND AVOID CONCEPT HAS MANY SHORTCOMINGS. FORTUNATELY IT WORKED IN THIS CASE FOR US, BUT NOT BY MUCH! THIS ENTIRE EVENT JUST SERVES TO REINFORCE IN ME THE ABSOLUTE NECESSITY TO REMAIN LARGELY OUTSIDE THE COCKPIT IN VMC.

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.