Widebody transport descended to 10000 rather than the 11000' claimed by ATC.

Attributes
ACN	92641
Time
Date	198808
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : oak airport : sfo
State Reference	CA
Altitude	msl bound lower : 10000 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : oak
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 150 flight time total : 15000 flight time type : 1000
ASRS Report	92641
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 6500 flight time type : 150
ASRS Report	92638
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

We were on the published arrival to sfo when the controling agency started to vector the aircraft. Aircraft was on an assigned heading and at 11000' MSL. The controling agency, in rapid manner, told us to turn to 310 degrees, slow to 210 KTS and I understood him to say, 'maintain 10.' I read back the clearance. The first officer and second officer heard me read back the clearance. The first officer started a slow descent from 11000 to 10000' MSL. 2-3 mins after level off at 10000' the controller asked me, 'weren't you supposed to maintain 11000?' I said, 'no, I read back 10000.' we continued approach and landed at sfo.

Original NASA ASRS Text

Title: WDB DESCENDED TO 10000 RATHER THAN THE 11000' CLAIMED BY ATC.

Narrative: WE WERE ON THE PUBLISHED ARR TO SFO WHEN THE CTLING AGENCY STARTED TO VECTOR THE ACFT. ACFT WAS ON AN ASSIGNED HDG AND AT 11000' MSL. THE CTLING AGENCY, IN RAPID MANNER, TOLD US TO TURN TO 310 DEGS, SLOW TO 210 KTS AND I UNDERSTOOD HIM TO SAY, 'MAINTAIN 10.' I READ BACK THE CLRNC. THE F/O AND S/O HEARD ME READ BACK THE CLRNC. THE F/O STARTED A SLOW DSCNT FROM 11000 TO 10000' MSL. 2-3 MINS AFTER LEVEL OFF AT 10000' THE CTLR ASKED ME, 'WEREN'T YOU SUPPOSED TO MAINTAIN 11000?' I SAID, 'NO, I READ BACK 10000.' WE CONTINUED APCH AND LANDED AT SFO.

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.