MD80 crew had the autoplt autotrim system fail. An altitude overshoot was the result.

Attributes
ACN	533173
Time
Date	200112
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : ord.vor
State Reference	IL
Altitude	msl bound lower : 13000 msl bound upper : 13450
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	533173
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : autoplt trim light other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance none taken : detected after the fact
Consequence	other other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Autoplt malfunction altitude deviation. While approaching assigned altitude of 13000 ft with autoplt engaged in pms climb mode we were simultaneously given a heading change, clearance direct to elx, and a frequency change to ZAU. After observing rate of climb decrease and autothrottles retard to begin leveloff, both pilots were momentarily diverted from monitoring leveloff as captain changed heading select knob and FMS and first officer changed radio frequency. Captain observed aircraft climbing through 13100 ft with autoplt trim light illuminated. 13000 ft was properly set and armed. Autoplt was disengaged and power reduced by 13200 ft. Aircraft was trimmed nose up and aircraft pitched up noticeably before forward pressure on yoke and retrimming arrested climb at approximately 13450 ft. As aircraft descended through 13200 ft ATC cleared us to climb to FL230. No comment made about altitude deviation. Seatbelt sign was illuminated but some passenger were probably startled by thrump of autoplt disconnect, abrupt maneuver, and a little lightness in seat. We determined that autoplt/alternate trim was inoperative. Subsequently retrimmed aircraft manually with primary trim whenever airspeed or confign changes were made. Malfunction entered in aircraft logbook.

Original NASA ASRS Text

Title: MD80 CREW HAD THE AUTOPLT AUTOTRIM SYS FAIL. AN ALT OVERSHOOT WAS THE RESULT.

Narrative: AUTOPLT MALFUNCTION ALTDEV. WHILE APCHING ASSIGNED ALT OF 13000 FT WITH AUTOPLT ENGAGED IN PMS CLB MODE WE WERE SIMULTANEOUSLY GIVEN A HEADING CHANGE, CLRNC DIRECT TO ELX, AND A FREQ CHANGE TO ZAU. AFTER OBSERVING RATE OF CLB DECREASE AND AUTOTHROTTLES RETARD TO BEGIN LEVELOFF, BOTH PLTS WERE MOMENTARILY DIVERTED FROM MONITORING LEVELOFF AS CAPT CHANGED HEADING SELECT KNOB AND FMS AND FO CHANGED RADIO FREQ. CAPT OBSERVED ACFT CLBING THROUGH 13100 FT WITH AUTOPLT TRIM LIGHT ILLUMINATED. 13000 FT WAS PROPERLY SET AND ARMED. AUTOPLT WAS DISENGAGED AND PWR REDUCED BY 13200 FT. ACFT WAS TRIMMED NOSE UP AND ACFT PITCHED UP NOTICEABLY BEFORE FORWARD PRESSURE ON YOKE AND RETRIMMING ARRESTED CLB AT APPROX 13450 FT. AS ACFT DSNDED THROUGH 13200 FT ATC CLRED US TO CLB TO FL230. NO COMMENT MADE ABOUT ALTDEV. SEATBELT SIGN WAS ILLUMINATED BUT SOME PAX WERE PROBABLY STARTLED BY THRUMP OF AUTOPLT DISCONNECT, ABRUPT MANEUVER, AND A LITTLE LIGHTNESS IN SEAT. WE DETERMINED THAT AUTOPLT/ALTERNATE TRIM WAS INOP. SUBSEQUENTLY RETRIMMED ACFT MANUALLY WITH PRIMARY TRIM WHENEVER AIRSPD OR CONFIGN CHANGES WERE MADE. MALFUNCTION ENTERED IN ACFT LOGBOOK.

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.