A BE1900 PIC descends 400 ft below his assigned altitude on the localizer for runway 23L at cle, oh.

Attributes
ACN	504320
Time
Date	200103
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : cle.airport
State Reference	OH
Altitude	msl bound lower : 9600 msl bound upper : 10000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : cle.tracon
Operator	common carrier : air carrier
Make Model Name	Beech 1900
Operating Under FAR Part	Part 135
Navigation In Use	ils localizer & glide slope : 23l
Flight Phase	descent : vacating altitude
Route In Use	approach : straight in approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 200 flight time total : 2000 flight time type : 3000
ASRS Report	504320
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : alt alerter other flight crewa
Resolutory Action	flight crew : became reoriented flight crew : returned to assigned altitude
Supplementary
Problem Areas	Aircraft ATC Human Performance Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While on approach to runway 23L ILS at 11000 ft, controller advised 'descend to 10000 ft.' we normally receive descent to 9000 ft. Captain was flying and continued past 10000 ft to 9600 ft. First officer noted altitude alerter tone and noted altitude deviation. Advised captain altitude should be 10000 ft and confirmed with ATC -- captain thought was 9000 ft. Immediately returned to 10000 ft. Contributing factors: normally receive descent to 9000 ft on approach. Altitude alerter sometimes disregarded when only 1000 ft change encoded as always goes off.

Original NASA ASRS Text

Title: A BE1900 PIC DSNDS 400 FT BELOW HIS ASSIGNED ALT ON THE LOC FOR RWY 23L AT CLE, OH.

Narrative: WHILE ON APCH TO RWY 23L ILS AT 11000 FT, CTLR ADVISED 'DSND TO 10000 FT.' WE NORMALLY RECEIVE DSCNT TO 9000 FT. CAPT WAS FLYING AND CONTINUED PAST 10000 FT TO 9600 FT. FO NOTED ALT ALERTER TONE AND NOTED ALTDEV. ADVISED CAPT ALT SHOULD BE 10000 FT AND CONFIRMED WITH ATC -- CAPT THOUGHT WAS 9000 FT. IMMEDIATELY RETURNED TO 10000 FT. CONTRIBUTING FACTORS: NORMALLY RECEIVE DSCNT TO 9000 FT ON APCH. ALT ALERTER SOMETIMES DISREGARDED WHEN ONLY 1000 FT CHANGE ENCODED AS ALWAYS GOES OFF.

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.