A B757-700 flight crew descended through cleared altitude when they misinterpreted ATC clearance.

Attributes
ACN	719255
Time
Date	200612
Place
Locale Reference	navaid : sqs.vortac
State Reference	MS
Altitude	msl bound lower : 29000 msl bound upper : 31000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : ztl.artcc
Operator	common carrier : air carrier
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 252 flight time type : 10000
ASRS Report	719255
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

Cruising at FL350; the controller comes on the radio and asked us if we could be through FL290 in 2 mins or less. We had a very strong tailwind and had used 3200 FPM descent rate to get from FL410 to FL350; so we said no problem. The next words out of the controller's mouth were to descend to FL310. We read back FL310 but the first officer put in 290 in the altitude window. I failed to xchk the number in the window before I started the descent. Passing through FL300; I asked the first officer if I had missed a radio call for descent to FL290; I stated my concern to the first officer about our descent to FL290; I thought we had a descent to FL310. About that time the controller called and asked if we would check our altitude. He asked us what altitude we were cleared to and we replied FL290. He then cleared us to FL240 without further incident.

Original NASA ASRS Text

Title: A B757-700 FLT CREW DSNDED THROUGH CLRED ALT WHEN THEY MISINTERPRETED ATC CLRNC.

Narrative: CRUISING AT FL350; THE CTLR COMES ON THE RADIO AND ASKED US IF WE COULD BE THROUGH FL290 IN 2 MINS OR LESS. WE HAD A VERY STRONG TAILWIND AND HAD USED 3200 FPM DSCNT RATE TO GET FROM FL410 TO FL350; SO WE SAID NO PROB. THE NEXT WORDS OUT OF THE CTLR'S MOUTH WERE TO DSND TO FL310. WE READ BACK FL310 BUT THE FO PUT IN 290 IN THE ALT WINDOW. I FAILED TO XCHK THE NUMBER IN THE WINDOW BEFORE I STARTED THE DSCNT. PASSING THROUGH FL300; I ASKED THE FO IF I HAD MISSED A RADIO CALL FOR DSCNT TO FL290; I STATED MY CONCERN TO THE FO ABOUT OUR DSCNT TO FL290; I THOUGHT WE HAD A DSCNT TO FL310. ABOUT THAT TIME THE CTLR CALLED AND ASKED IF WE WOULD CHK OUR ALT. HE ASKED US WHAT ALT WE WERE CLRED TO AND WE REPLIED FL290. HE THEN CLRED US TO FL240 WITHOUT FURTHER INCIDENT.

Data retrieved from NASA's ASRS site as of January 2009 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.