A B737-300 flight crew calls ATC with a traffic problem as TCASII notes crossing traffic below. The B737 had last received a clearance descent through that occupied altitude with ZOA. Ca.

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Attributes
ACN	456417
Time
Date	199912
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : oak.vor
State Reference	CA
Altitude	msl bound lower : 11500 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	descent : vacating altitude descent : approach
Route In Use	arrival star : big sur 2
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zoa.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : atp pilot : cfi pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 240 flight time total : 12000 flight time type : 2700
ASRS Report	456417
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 7000 flight time type : 1000
ASRS Report	457136
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	aircraft equipment : tcas other flight crewa other flight crewb
Resolutory Action	controller : separated traffic flight crew : took precautionary avoidance action other
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 12000 vertical : 500
Supplementary
Problem Areas	Airspace Structure ATC Human Performance Flight Crew Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

On big sur 2 arrival to sfo, just prior to boldr, descending through 11800 ft, we saw an aircraft about 2 mi at 12 O'clock position on TCASII at 11000 ft. Asked center if he knew about aircraft at 11000 ft, and he said 'that is why I cleared you to 12000 ft.' both the first officer and myself clearly remember the clearance as 'cross boldr at 10000 ft. I told the controller the last clearance we had was 'boldr at 10000 ft' and he said 'must have been my mistake, level at 12000 ft.' we stopped the descent at about 11400 ft and started a climb to 12000 ft as we passed over the other aircraft. Then we were cleared to 10000 ft. Supplemental information from acn 457136: we had been cleared to stop descent at 12000 ft. We did not acknowledge or receive such a clearance/transmission. The controller stated that he must not have received our readback after he allegedly gave us the amended 12000 ft clearance.

Original NASA ASRS Text

Title: A B737-300 FLC CALLS ATC WITH A TFC PROB AS TCASII NOTES XING TFC BELOW. THE B737 HAD LAST RECEIVED A CLRNC DSCNT THROUGH THAT OCCUPIED ALT WITH ZOA. CA.

Narrative: ON BIG SUR 2 ARR TO SFO, JUST PRIOR TO BOLDR, DSNDING THROUGH 11800 FT, WE SAW AN ACFT ABOUT 2 MI AT 12 O'CLOCK POS ON TCASII AT 11000 FT. ASKED CTR IF HE KNEW ABOUT ACFT AT 11000 FT, AND HE SAID 'THAT IS WHY I CLRED YOU TO 12000 FT.' BOTH THE FO AND MYSELF CLRLY REMEMBER THE CLRNC AS 'CROSS BOLDR AT 10000 FT. I TOLD THE CTLR THE LAST CLRNC WE HAD WAS 'BOLDR AT 10000 FT' AND HE SAID 'MUST HAVE BEEN MY MISTAKE, LEVEL AT 12000 FT.' WE STOPPED THE DSCNT AT ABOUT 11400 FT AND STARTED A CLB TO 12000 FT AS WE PASSED OVER THE OTHER ACFT. THEN WE WERE CLRED TO 10000 FT. SUPPLEMENTAL INFO FROM ACN 457136: WE HAD BEEN CLRED TO STOP DSCNT AT 12000 FT. WE DID NOT ACKNOWLEDGE OR RECEIVE SUCH A CLRNC/XMISSION. THE CTLR STATED THAT HE MUST NOT HAVE RECEIVED OUR READBACK AFTER HE ALLEGEDLY GAVE US THE AMENDED 12000 FT CLRNC.

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.