ZSE controller loses situational awareness and descends a DHC8 into a conflicting B737.

Attributes
ACN	505377
Time
Date	200103
Day	Sun
Local Time Of Day	0601 To 1200
Place
State Reference	WA
Altitude	msl single value : 24000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zse.artcc
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Route In Use	enroute other
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zse.artcc
Operator	common carrier : air carrier
Make Model Name	Dash 8-200
Operating Under FAR Part	Part 121
Flight Phase	cruise : enroute altitude change
Route In Use	enroute other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 13 controller time certified in position1 : 12.75
ASRS Report	505377
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment : conflict alert other other : conflict alert
Resolutory Action	none taken : detected after the fact
Miss Distance	horizontal : 22700 vertical : 700
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Sequencing a string of aircraft inbound to sea with a DHC8 going from pdx to geg at FL250 crossing the stream. The DHC8 requested to start his descent into geg. I issued FL240 which was the floor of my airspace. I did not see the conflicting B737 which was directly under the DHC8 at the time. I think the reason this occurred is that I had just finished sequencing all the sea arrs and I

Original NASA ASRS Text

Title: ZSE CTLR LOSES SITUATIONAL AWARENESS AND DSNDS A DHC8 INTO A CONFLICTING B737.

Narrative: SEQUENCING A STRING OF ACFT INBOUND TO SEA WITH A DHC8 GOING FROM PDX TO GEG AT FL250 XING THE STREAM. THE DHC8 REQUESTED TO START HIS DSCNT INTO GEG. I ISSUED FL240 WHICH WAS THE FLOOR OF MY AIRSPACE. I DID NOT SEE THE CONFLICTING B737 WHICH WAS DIRECTLY UNDER THE DHC8 AT THE TIME. I THINK THE REASON THIS OCCURRED IS THAT I HAD JUST FINISHED SEQUENCING ALL THE SEA ARRS AND I

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.