Air carrier crew misunderstands clearance.

Attributes
ACN	455300
Time
Date	199911
Day	Wed
Local Time Of Day	1801 To 2400
Place
State Reference	FL
Altitude	msl bound lower : 24800 msl bound upper : 27000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zjx.artcc
Operator	common carrier : air carrier
Make Model Name	Medium Transport, Low Wing, 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : multi engine
Experience	flight time last 90 days : 240 flight time total : 14000 flight time type : 5000
ASRS Report	455300
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

At a cruise altitude of FL290, ATC called us and told us to descend to FL240 to cross clawz intersection. I read back the clearance with the altitude of FL240 at clawz with our call sign. The ATC controller called us at FL248 and asked us our altitude, we told him and then he said that we only were cleared to FL270. We told him that we understood that we were cleared to FL240.

Original NASA ASRS Text

Title: ACR CREW MISUNDERSTANDS CLRNC.

Narrative: AT A CRUISE ALT OF FL290, ATC CALLED US AND TOLD US TO DSND TO FL240 TO CROSS CLAWZ INTXN. I READ BACK THE CLRNC WITH THE ALT OF FL240 AT CLAWZ WITH OUR CALL SIGN. THE ATC CTLR CALLED US AT FL248 AND ASKED US OUR ALT, WE TOLD HIM AND THEN HE SAID THAT WE ONLY WERE CLRED TO FL270. WE TOLD HIM THAT WE UNDERSTOOD THAT WE WERE CLRED TO FL240.

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.