MD80 crew had altitude deviation.

Attributes
ACN	469196
Time
Date	200004
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zoa.artcc
State Reference	CA
Altitude	msl bound lower : 29000 msl bound upper : 29500
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zoa.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	469196
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : returned to assigned altitude none taken : insufficient time
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Trim failure/altitude deviation. While leveling at FL290 and accelerating to cruise speed with the autoplt engaged, the altitude trim motor failed, causing the aircraft to climb even though altitude hold was annunciated on the FMA. The autoplt was disconnected and the aircraft retrimmed using the primary trim motor. Cruise altitude was exceeded by 500 ft. After several mins the altitude trim started functioning again and the flight was continued to destination without further incident.

Original NASA ASRS Text

Title: MD80 CREW HAD ALTDEV.

Narrative: TRIM FAILURE/ALTDEV. WHILE LEVELING AT FL290 AND ACCELERATING TO CRUISE SPD WITH THE AUTOPLT ENGAGED, THE ALT TRIM MOTOR FAILED, CAUSING THE ACFT TO CLB EVEN THOUGH ALT HOLD WAS ANNUNCIATED ON THE FMA. THE AUTOPLT WAS DISCONNECTED AND THE ACFT RETRIMMED USING THE PRIMARY TRIM MOTOR. CRUISE ALT WAS EXCEEDED BY 500 FT. AFTER SEVERAL MINS THE ALT TRIM STARTED FUNCTIONING AGAIN AND THE FLT WAS CONTINUED TO DEST WITHOUT FURTHER INCIDENT.

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.