ARTCC controller descended a widebody transport through altitude of small transport with what appeared to be less than standard separation. Operational error.

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Attributes
ACN	93587
Time
Date	198809
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : sfo
State Reference	CA
Altitude	msl bound lower : 21650 msl bound upper : 22000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa
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	enroute airway : zoa
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 14000 flight time type : 2000
ASRS Report	93587
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	conflict : nmac non adherence : required legal separation
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Miss Distance	horizontal : 0 vertical : 350
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

On descent into sfo, at an intermediate altitude of FL260, oakland center asked if we could make it through FL220 in 1 1/2 minutes to maintain 16000'. We immediately started a 4000 FPM descent and were descending through 21650' when center called traffic at 12 O'clock. Our altitude of 21650' was achieved exactly 1 min from instructions by center. Vertical sep at 1 min after descent was started appeared to be 500' +/-. Traffic appeared to be small turboprop. If our altitude had been 22000 in 1 1/2 minutes it would have resulted in a midair.

Original NASA ASRS Text

Title: ARTCC CTLR DESCENDED A WDB THROUGH ALT OF SMT WITH WHAT APPEARED TO BE LESS THAN STANDARD SEPARATION. OPERATIONAL ERROR.

Narrative: ON DSCNT INTO SFO, AT AN INTERMEDIATE ALT OF FL260, OAKLAND CTR ASKED IF WE COULD MAKE IT THROUGH FL220 IN 1 1/2 MINUTES TO MAINTAIN 16000'. WE IMMEDIATELY STARTED A 4000 FPM DSCNT AND WERE DSNDING THROUGH 21650' WHEN CTR CALLED TFC AT 12 O'CLOCK. OUR ALT OF 21650' WAS ACHIEVED EXACTLY 1 MIN FROM INSTRUCTIONS BY CTR. VERTICAL SEP AT 1 MIN AFTER DSCNT WAS STARTED APPEARED TO BE 500' +/-. TFC APPEARED TO BE SMALL TURBOPROP. IF OUR ALT HAD BEEN 22000 IN 1 1/2 MINUTES IT WOULD HAVE RESULTED IN A MIDAIR.

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.