Air carrier came in close proximity to an small transport while in a descent. No traffic was issued.

Attributes
ACN	116741
Time
Date	198907
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : san
State Reference	CA
Altitude	msl bound lower : 15500 msl bound upper : 16000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : san
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent other
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Small Transport
Flight Phase	cruise other
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : atp
Experience	flight time last 90 days : 200 flight time total : 20000 flight time type : 2000
ASRS Report	116741
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	non adherence : far other anomaly other other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 500 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

We were on descent into san, in contact with approach control, and cleared to 12,000'. While passing thru 16,000' I had to level off very abruptly to avoid hitting an small transport cruising at 15,500' at a 90 degree crossing angle. I immediately questioned san approach control. They replied that they had no one there on radar and that it was center's airspace, and they would check with them. Seat belt was on at the time and no one was injured in the level off. I asked approach control how they could not see him if he was squawking as lax center indicated. The WX was clear but we had no knowledge that anyone was in our area.

Original NASA ASRS Text

Title: ACR CAME IN CLOSE PROX TO AN SMT WHILE IN A DESCENT. NO TRAFFIC WAS ISSUED.

Narrative: WE WERE ON DSCNT INTO SAN, IN CONTACT WITH APCH CTL, AND CLRED TO 12,000'. WHILE PASSING THRU 16,000' I HAD TO LEVEL OFF VERY ABRUPTLY TO AVOID HITTING AN SMT CRUISING AT 15,500' AT A 90 DEG XING ANGLE. I IMMEDIATELY QUESTIONED SAN APCH CTL. THEY REPLIED THAT THEY HAD NO ONE THERE ON RADAR AND THAT IT WAS CENTER'S AIRSPACE, AND THEY WOULD CHECK WITH THEM. SEAT BELT WAS ON AT THE TIME AND NO ONE WAS INJURED IN THE LEVEL OFF. I ASKED APCH CTL HOW THEY COULD NOT SEE HIM IF HE WAS SQUAWKING AS LAX CENTER INDICATED. THE WX WAS CLEAR BUT WE HAD NO KNOWLEDGE THAT ANYONE WAS IN OUR AREA.

Data retrieved from NASA's ASRS site as of August 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.