MD80 overshoots cleared flight level when autoplt commands increased rate of climb vice leveloff.

Attributes
ACN	692475
Time
Date	200603
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : emg.vortac
State Reference	LA
Altitude	msl single value : 34800
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zhu.artcc
Operator	common carrier : air carrier
Make Model Name	MD-83
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 : first officer
ASRS Report	692475
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	692180
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllerb other flight crewa other flight crewb
Resolutory Action	aircraft : equipment problem dissipated flight crew : returned to assigned altitude flight crew : overcame equipment problem
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Climbing to FL350; autoplt #2 engaged in IAS/mach (.760 mach selected) and EPR lim on the autothrottle. FMA presented normal altitude capture and altitude hold; but at approximately FL348 the nose pitched up and vertical speed increased to 1200-1500 FPM. As the vertical speed increased; I immediately disengaged the autoplt and recovered to FL350. Maximum deviation to FL355. Back on altitude in about 15 seconds. At FL355 ZHU queried our assigned altitude. We confirmed FL350 and that we had experienced an autoplt malfunction and were correcting. Autoplt functioned normally for the rest of the flight.

Original NASA ASRS Text

Title: MD80 OVERSHOOTS CLRED FLT LEVEL WHEN AUTOPLT COMMANDS INCREASED RATE OF CLB VICE LEVELOFF.

Narrative: CLBING TO FL350; AUTOPLT #2 ENGAGED IN IAS/MACH (.760 MACH SELECTED) AND EPR LIM ON THE AUTOTHROTTLE. FMA PRESENTED NORMAL ALT CAPTURE AND ALT HOLD; BUT AT APPROX FL348 THE NOSE PITCHED UP AND VERT SPD INCREASED TO 1200-1500 FPM. AS THE VERT SPD INCREASED; I IMMEDIATELY DISENGAGED THE AUTOPLT AND RECOVERED TO FL350. MAX DEV TO FL355. BACK ON ALT IN ABOUT 15 SECONDS. AT FL355 ZHU QUERIED OUR ASSIGNED ALT. WE CONFIRMED FL350 AND THAT WE HAD EXPERIENCED AN AUTOPLT MALFUNCTION AND WERE CORRECTING. AUTOPLT FUNCTIONED NORMALLY FOR THE REST OF THE FLT.

Data retrieved from NASA's ASRS site as of January 2009 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.