The crew was issued a descent clearance which the captain and first officer heard different altitudes. The captain read back the wrong altitude and neither the controller nor the first officer noticed the error. The controller alerted the crew when they were passing 1000 ft below the assigned altitude and then issued a new altitude.

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Attributes
ACN	417680
Time
Date	199810
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : rda
State Reference	VA
Altitude	msl bound lower : 27800 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Challenger CL604
Operating Under FAR Part	Part 121
Navigation In Use	Other Other other vortac
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 99 flight time total : 6100 flight time type : 99
ASRS Report	417680
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Cruising at FL330, given clearance to a lower flight level. I understood FL290 and set it accordingly. I began to program the FMS and was advised by captain new clearance was to FL240. I set FMS and autoplt accordingly. After receiving the clearance, the captain acknowledged center responding with FL240. I did not notice the difference between his readback and my autoplt setting of FL290. At FL280 and descending, center advised our clearance was to FL290. I arrested the descent at about FL278. Captain responded to center he understood clearance to FL240 and read that back. Center then cleared us to FL270. Probable cause: I did not question the discrepancy between my autoplt setting and the altitude the captain advised to set in the FMS. Future prevention: noticing and questioning altitude discrepancies.

Original NASA ASRS Text

Title: THE CREW WAS ISSUED A DSCNT CLRNC WHICH THE CAPT AND FO HEARD DIFFERENT ALTS. THE CAPT READ BACK THE WRONG ALT AND NEITHER THE CTLR NOR THE FO NOTICED THE ERROR. THE CTLR ALERTED THE CREW WHEN THEY WERE PASSING 1000 FT BELOW THE ASSIGNED ALT AND THEN ISSUED A NEW ALT.

Narrative: CRUISING AT FL330, GIVEN CLRNC TO A LOWER FLT LEVEL. I UNDERSTOOD FL290 AND SET IT ACCORDINGLY. I BEGAN TO PROGRAM THE FMS AND WAS ADVISED BY CAPT NEW CLRNC WAS TO FL240. I SET FMS AND AUTOPLT ACCORDINGLY. AFTER RECEIVING THE CLRNC, THE CAPT ACKNOWLEDGED CTR RESPONDING WITH FL240. I DID NOT NOTICE THE DIFFERENCE BTWN HIS READBACK AND MY AUTOPLT SETTING OF FL290. AT FL280 AND DSNDING, CTR ADVISED OUR CLRNC WAS TO FL290. I ARRESTED THE DSCNT AT ABOUT FL278. CAPT RESPONDED TO CTR HE UNDERSTOOD CLRNC TO FL240 AND READ THAT BACK. CTR THEN CLRED US TO FL270. PROBABLE CAUSE: I DID NOT QUESTION THE DISCREPANCY BTWN MY AUTOPLT SETTING AND THE ALT THE CAPT ADVISED TO SET IN THE FMS. FUTURE PREVENTION: NOTICING AND QUESTIONING ALT DISCREPANCIES.

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.