Loss of separation between an air carrier B737 and a commuter E120 at 10000 ft.

Attributes
ACN	401020
Time
Date	199804
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : olm airport : sea
State Reference	WA
Altitude	msl bound lower : 10000 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : sea
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Xingu EMB-121 All Series
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : private pilot : instrument pilot : flight engineer pilot : commercial pilot : atp
Experience	flight time last 90 days : 120 flight time total : 7500 flight time type : 1400
ASRS Report	401020
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	other other : other pilot : atp
Experience	flight time last 90 days : 200 flight time total : 10000 flight time type : 3000
ASRS Report	400817
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : clearance
Independent Detector	other controllera
Resolutory Action	none taken : detected after the fact other
Consequence	Other
Miss Distance	horizontal : 19000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While on the olympia two arrival to seattle after passing olm VOR, ATC approach control gave us a descent from 12000 ft to (we thought) 10000 ft. We were also told we had traffic we were passing at 10 O'clock position which we had in sight. We read back descent to 10000 ft and verified (both pilots per company policy) in the altitude alerter. Shortly after this ATC said there was a new ATIS. I went off the ATC frequency to get the ATIS. While off, the PF was told we were given 11000 ft after we were already level at 10000 ft. Traffic didn't seem to be a factor and no TCASII alerts.

Original NASA ASRS Text

Title: LOSS OF SEPARATION BTWN AN ACR B737 AND A COMMUTER E120 AT 10000 FT.

Narrative: WHILE ON THE OLYMPIA TWO ARR TO SEATTLE AFTER PASSING OLM VOR, ATC APCH CTL GAVE US A DSCNT FROM 12000 FT TO (WE THOUGHT) 10000 FT. WE WERE ALSO TOLD WE HAD TFC WE WERE PASSING AT 10 O'CLOCK POS WHICH WE HAD IN SIGHT. WE READ BACK DSCNT TO 10000 FT AND VERIFIED (BOTH PLTS PER COMPANY POLICY) IN THE ALT ALERTER. SHORTLY AFTER THIS ATC SAID THERE WAS A NEW ATIS. I WENT OFF THE ATC FREQ TO GET THE ATIS. WHILE OFF, THE PF WAS TOLD WE WERE GIVEN 11000 FT AFTER WE WERE ALREADY LEVEL AT 10000 FT. TFC DIDN'T SEEM TO BE A FACTOR AND NO TCASII ALERTS.

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.