Dhc-8 flight crew received RA during arrival into sea.

Attributes
ACN	554461
Time
Date	200207
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : olm.vortac
State Reference	WA
Altitude	msl single value : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : s46.tracon
Operator	common carrier : air carrier
Make Model Name	Dash 8-200
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : olm 4
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zse.artcc
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : olm 4
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 150 flight time total : 12000 flight time type : 5000
ASRS Report	554461
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne critical non adherence : required legal separation
Independent Detector	aircraft equipment : tcas other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were cleared to cross 10 NM south of ocm at 10000 ft. Approaching the ocm VOR, we noticed a TCASII target descending above and behind us. As the target descended below 11000 ft, we received an RA to descend at 3000 FPM. I notified sea approach we were performing an RA and sea advised aircraft Y the other aircraft to climb and maintain 11000 ft. Aircraft Y said at that point that they had us in sight. The lowest number I noticed on the TCAS was 500 ft. We never heard any radio xmissions from aircraft Y prior to the event. We found out from sea approach that aircraft Y had been cleared by ZSE to 'descend via the ocm arrival.' aircraft Y crew read the plate and used the 'turboprop' altitude of 10000 ft instead of the 'turbojet' altitude of 12000 ft. I would like to know what the TCASII showed in aircraft Y's cockpit. Use of the 'descend via' clearance should not be used when it includes an altitude assignment. If this procedure is not changed, this will happen again.

Original NASA ASRS Text

Title: DHC-8 FLC RECEIVED RA DURING ARR INTO SEA.

Narrative: WE WERE CLRED TO CROSS 10 NM S OF OCM AT 10000 FT. APCHING THE OCM VOR, WE NOTICED A TCASII TARGET DSNDING ABOVE AND BEHIND US. AS THE TARGET DSNDED BELOW 11000 FT, WE RECEIVED AN RA TO DSND AT 3000 FPM. I NOTIFIED SEA APCH WE WERE PERFORMING AN RA AND SEA ADVISED ACFT Y THE OTHER ACFT TO CLB AND MAINTAIN 11000 FT. ACFT Y SAID AT THAT POINT THAT THEY HAD US IN SIGHT. THE LOWEST NUMBER I NOTICED ON THE TCAS WAS 500 FT. WE NEVER HEARD ANY RADIO XMISSIONS FROM ACFT Y PRIOR TO THE EVENT. WE FOUND OUT FROM SEA APCH THAT ACFT Y HAD BEEN CLRED BY ZSE TO 'DSND VIA THE OCM ARR.' ACFT Y CREW READ THE PLATE AND USED THE 'TURBOPROP' ALT OF 10000 FT INSTEAD OF THE 'TURBOJET' ALT OF 12000 FT. I WOULD LIKE TO KNOW WHAT THE TCASII SHOWED IN ACFT Y'S COCKPIT. USE OF THE 'DSND VIA' CLRNC SHOULD NOT BE USED WHEN IT INCLUDES AN ALT ASSIGNMENT. IF THIS PROC IS NOT CHANGED, THIS WILL HAPPEN AGAIN.

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.