Thinking they were cleared to 10000 ft, flight crew overshot assigned altitude of 11000 ft.

Attributes
ACN	344960
Time
Date	199608
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : buf
State Reference	NY
Altitude	msl bound lower : 10500 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob tower : bis
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 180 flight time total : 13000 flight time type : 9000
ASRS Report	344960
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude 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:

Cruising eastbound at about FL280 en route to buf, given a clearance similar to this: XXX cross 30 mi west of buf at 10000 ft, 250 KTS, buf altimeter 30.10 inches.' about 40 mi west of buf, controller asked us to verify level 11000 ft. We were at 10500 ft and quickly returned to 11000 ft. No urgency or conflict was noted in controller's voice. All 3 of us thought we heard 10000 ft. We called out of FL280 for 10000 ft, and did not hear a correction from the controller. If we were possibly at fault, this could be another case of a clearance being issued with too many numbers, ie, flight number, altitude, distance, airspeed, and altimeter (30.10 inches), not 10000 ft! In visual conditions, daylight, light traffic, I do not believe there was any conflict. The controller did not seem alarmed and didn't say anything to indicate a problem. Nevertheless, there was a misunderstanding that should be noted.

Original NASA ASRS Text

Title: THINKING THEY WERE CLRED TO 10000 FT, FLC OVERSHOT ASSIGNED ALT OF 11000 FT.

Narrative: CRUISING EBOUND AT ABOUT FL280 ENRTE TO BUF, GIVEN A CLRNC SIMILAR TO THIS: XXX CROSS 30 MI W OF BUF AT 10000 FT, 250 KTS, BUF ALTIMETER 30.10 INCHES.' ABOUT 40 MI W OF BUF, CTLR ASKED US TO VERIFY LEVEL 11000 FT. WE WERE AT 10500 FT AND QUICKLY RETURNED TO 11000 FT. NO URGENCY OR CONFLICT WAS NOTED IN CTLR'S VOICE. ALL 3 OF US THOUGHT WE HEARD 10000 FT. WE CALLED OUT OF FL280 FOR 10000 FT, AND DID NOT HEAR A CORRECTION FROM THE CTLR. IF WE WERE POSSIBLY AT FAULT, THIS COULD BE ANOTHER CASE OF A CLRNC BEING ISSUED WITH TOO MANY NUMBERS, IE, FLT NUMBER, ALT, DISTANCE, AIRSPD, AND ALTIMETER (30.10 INCHES), NOT 10000 FT! IN VISUAL CONDITIONS, DAYLIGHT, LIGHT TFC, I DO NOT BELIEVE THERE WAS ANY CONFLICT. THE CTLR DID NOT SEEM ALARMED AND DIDN'T SAY ANYTHING TO INDICATE A PROB. NEVERTHELESS, THERE WAS A MISUNDERSTANDING THAT SHOULD BE NOTED.

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.