Altitude deviation descended below cleared altitude.

Attributes
ACN	112982
Time
Date	198906
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : sea
State Reference	WA
Altitude	msl bound lower : 10300 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sea tower : dfw
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 15000 flight time type : 20
ASRS Report	112982
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : commercial pilot : instrument
Experience	flight time last 90 days : 140 flight time total : 9622 flight time type : 8658
ASRS Report	112981
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On flight xx from sfo to sea we had been cleared for the finney #3 arrival. This approach calls for the crossing of grame intersection, 30 DME on the sea VOR 058 right, at 10,000' and 250 KTS. As captain I was flying and my first officer was working the radios. At approximately 13,000' ATC advised a twin engine aircraft at 10,000'. At that time we advised ATC no joy. Immediately after our call the twin advised ATC that he had us in sight. I then queried my first officer as to our descent to 10,000 due to the other aircraft. At that time he looked out the right side of the aircraft and advised the twin in sight and well clear of us. We then continued our descent and at approximately 10,500 ATC called and advised us we were only cleared to 11,000'. I immediately climbed back to 11,000' while my first officer asked where we were cleared to 11,000 as he was sure we had been cleared to 10,000. After approximately 1-2 minutes we were then cleared to 10,000 and we completed a normal arrival and landing. My first officer who had set the 10,000 in the altitude alert stated then and now that he never heard ATC advise 11,000'. I also obviously never heard it or I would not have descended below 11,000' and I would not have checked with my first officer that we were clear of the twin before starting descent to 10,000. As to a contributing factor if in fact ATC did clear us to 11,000 and both my first officer and I missed the call it would be that we were on the finney arrival and it called for 10,000'.

Original NASA ASRS Text

Title: ALT DEVIATION DESCENDED BELOW CLEARED ALT.

Narrative: ON FLT XX FROM SFO TO SEA WE HAD BEEN CLRED FOR THE FINNEY #3 ARR. THIS APCH CALLS FOR THE XING OF GRAME INTXN, 30 DME ON THE SEA VOR 058 R, AT 10,000' AND 250 KTS. AS CAPT I WAS FLYING AND MY F/O WAS WORKING THE RADIOS. AT APPROX 13,000' ATC ADVISED A TWIN ENGINE ACFT AT 10,000'. AT THAT TIME WE ADVISED ATC NO JOY. IMMEDIATELY AFTER OUR CALL THE TWIN ADVISED ATC THAT HE HAD US IN SIGHT. I THEN QUERIED MY F/O AS TO OUR DSCNT TO 10,000 DUE TO THE OTHER ACFT. AT THAT TIME HE LOOKED OUT THE RIGHT SIDE OF THE ACFT AND ADVISED THE TWIN IN SIGHT AND WELL CLEAR OF US. WE THEN CONTINUED OUR DSCNT AND AT APPROX 10,500 ATC CALLED AND ADVISED US WE WERE ONLY CLRED TO 11,000'. I IMMEDIATELY CLIMBED BACK TO 11,000' WHILE MY F/O ASKED WHERE WE WERE CLRED TO 11,000 AS HE WAS SURE WE HAD BEEN CLRED TO 10,000. AFTER APPROX 1-2 MINUTES WE WERE THEN CLRED TO 10,000 AND WE COMPLETED A NORMAL ARR AND LNDG. MY F/O WHO HAD SET THE 10,000 IN THE ALT ALERT STATED THEN AND NOW THAT HE NEVER HEARD ATC ADVISE 11,000'. I ALSO OBVIOUSLY NEVER HEARD IT OR I WOULD NOT HAVE DESCENDED BELOW 11,000' AND I WOULD NOT HAVE CHECKED WITH MY F/O THAT WE WERE CLEAR OF THE TWIN BEFORE STARTING DSCNT TO 10,000. AS TO A CONTRIBUTING FACTOR IF IN FACT ATC DID CLEAR US TO 11,000 AND BOTH MY F/O AND I MISSED THE CALL IT WOULD BE THAT WE WERE ON THE FINNEY ARR AND IT CALLED FOR 10,000'.

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.