Loss of separation and operational error results when flight cleared through occupied altitude.

Attributes
ACN	461600
Time
Date	200001
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : oak.airport
State Reference	CA
Altitude	msl single value : 36700
Environment
Flight Conditions	VMC
Weather Elements	Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	cruise : enroute altitude change
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 9000 flight time type : 300
ASRS Report	461600
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : multi engine pilot : commercial
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	aircraft equipment : tcas other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance
Miss Distance	horizontal : 24000 vertical : 300
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

We were at FL390 but due to a rough ride, we requested FL350. ZOA cleared us to FL350. We were descending at 1000 FPM. Passing FL367, we received a TCASII yellow TA. It was for opposite direction traffic at FL370. The closest we came was 300 ft vertical, and about 4 mi horizontal. No evasive action was taken. At that same time we increased descent rate to 2500 FPM. Also, ZOA turned us 30 degrees left away from the traffic. We leveled at FL350 and were cleared back on course. I believe that ZOA failed to give us proper horizontal separation during our descent.

Original NASA ASRS Text

Title: LOSS OF SEPARATION AND OPERROR RESULTS WHEN FLT CLRED THROUGH OCCUPIED ALT.

Narrative: WE WERE AT FL390 BUT DUE TO A ROUGH RIDE, WE REQUESTED FL350. ZOA CLRED US TO FL350. WE WERE DSNDING AT 1000 FPM. PASSING FL367, WE RECEIVED A TCASII YELLOW TA. IT WAS FOR OPPOSITE DIRECTION TFC AT FL370. THE CLOSEST WE CAME WAS 300 FT VERT, AND ABOUT 4 MI HORIZ. NO EVASIVE ACTION WAS TAKEN. AT THAT SAME TIME WE INCREASED DSCNT RATE TO 2500 FPM. ALSO, ZOA TURNED US 30 DEGS L AWAY FROM THE TFC. WE LEVELED AT FL350 AND WERE CLRED BACK ON COURSE. I BELIEVE THAT ZOA FAILED TO GIVE US PROPER HORIZ SEPARATION DURING OUR DSCNT.

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.