Altitude deviation overshoot on descent.

Attributes
ACN	300264
Time
Date	199503
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pie
State Reference	FL
Altitude	msl bound lower : 22000 msl bound upper : 23000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zjx
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : instrument pilot : commercial
Experience	flight time last 90 days : 150 flight time total : 20000 flight time type : 4100
ASRS Report	300264
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	controller : issued new clearance flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

We were cleared to descend from FL330 to FL230. Altitude was armed in flight guidance with autoplt and autothrottles on. FMA displayed altitude capture then altitude hold. Several seconds later, the altitude audio warning sounded as the aircraft descended through 22700 ft. I selected vertical speed up 1000 FPM. The aircraft continued to descend and I noticed the autoplt trim light on steady. I disconnected the autoplt only to find very heavy nose down trim. By this time we were passing FL220 and I instructed the first officer to report our altitude to ATC, by the time he reached his microphone ATC instructed us to descend to 10000 ft. The aircraft handled fine with the autoplt off. A normal landing was made and the flight guidance was written in the aircraft maintenance log.

Original NASA ASRS Text

Title: ALTDEV OVERSHOOT ON DSCNT.

Narrative: WE WERE CLRED TO DSND FROM FL330 TO FL230. ALT WAS ARMED IN FLT GUIDANCE WITH AUTOPLT AND AUTOTHROTTLES ON. FMA DISPLAYED ALT CAPTURE THEN ALT HOLD. SEVERAL SECONDS LATER, THE ALT AUDIO WARNING SOUNDED AS THE ACFT DSNDED THROUGH 22700 FT. I SELECTED VERT SPD UP 1000 FPM. THE ACFT CONTINUED TO DSND AND I NOTICED THE AUTOPLT TRIM LIGHT ON STEADY. I DISCONNECTED THE AUTOPLT ONLY TO FIND VERY HVY NOSE DOWN TRIM. BY THIS TIME WE WERE PASSING FL220 AND I INSTRUCTED THE FO TO RPT OUR ALT TO ATC, BY THE TIME HE REACHED HIS MIKE ATC INSTRUCTED US TO DSND TO 10000 FT. THE ACFT HANDLED FINE WITH THE AUTOPLT OFF. A NORMAL LNDG WAS MADE AND THE FLT GUIDANCE WAS WRITTEN IN THE ACFT MAINT LOG.

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.