B757 pilot sets wrong altitude and descends through cleared altitude.

Attributes
ACN	455430
Time
Date	199910
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : pdz.vor
State Reference	CA
Altitude	msl bound lower : 23500 msl bound upper : 24000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zla.artcc
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 129
Navigation In Use	other
Flight Phase	cruise : enroute altitude change
Route In Use	arrival star : pdz.3
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : atp
Experience	flight time last 90 days : 135 flight time total : 16000 flight time type : 500
ASRS Report	455430
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : multi engine pilot : instrument
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued alert flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During descent IFR, pdz 3, we were cleared to descend from FL370 to FL240. In all frankness, I made an equivocal adjustment in the automatic pilot, setting 23.5 inadvertently. The controller called us to not descend off FL240. We recuperated immediately FL240. We changed frequency and the rest of the flight was normal.

Original NASA ASRS Text

Title: B757 PLT SETS WRONG ALT AND DSNDS THROUGH CLRED ALT.

Narrative: DURING DSCNT IFR, PDZ 3, WE WERE CLRED TO DSND FROM FL370 TO FL240. IN ALL FRANKNESS, I MADE AN EQUIVOCAL ADJUSTMENT IN THE AUTOMATIC PLT, SETTING 23.5 INADVERTENTLY. THE CTLR CALLED US TO NOT DSND OFF FL240. WE RECUPERATED IMMEDIATELY FL240. WE CHANGED FREQ AND THE REST OF THE FLT WAS NORMAL.

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.