A DC9-30 in cruise at FL330 deviated from the assigned altitude due to the autoplt altitude hold fun...

Attributes
ACN	432410
Time
Date	199903
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : rod.vortac
State Reference	OH
Altitude	msl bound lower : 32700 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zid.artcc
Operator	common carrier : air carrier
Make Model Name	DC-9 30
Operating Under FAR Part	Part 121
Navigation In Use	other vortac
Flight Phase	cruise : level landing : roll
Route In Use	enroute : on vectors
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : commercial pilot : flight engineer pilot : multi engine pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 17150 flight time type : 10000
ASRS Report	432410
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 150 flight time total : 4300 flight time type : 150
ASRS Report	432412
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : altitude alerting other controllerb other flight crewa other flight crewb
Resolutory Action	flight crew : regained aircraft control flight crew : returned to assigned airspace flight crew : overrode automation
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

A slight turn was begun and as turn developed, a slight climb began. When the aircraft was commanded to wings level, the climb rapidly turned into a descent between 500-700 FPM. Attempted to level aircraft using vertical speed control wheel. Descent continued. Autoplt disengaged and manual leveloff accomplished at FL327.

Original NASA ASRS Text

Title: A DC9-30 IN CRUISE AT FL330 DEVIATED FROM THE ASSIGNED ALT DUE TO THE AUTOPLT ALT HOLD FUNCTION FAILURE.

Narrative: A SLIGHT TURN WAS BEGUN AND AS TURN DEVELOPED, A SLIGHT CLB BEGAN. WHEN THE ACFT WAS COMMANDED TO WINGS LEVEL, THE CLB RAPIDLY TURNED INTO A DSCNT BTWN 500-700 FPM. ATTEMPTED TO LEVEL ACFT USING VERT SPD CTL WHEEL. DSCNT CONTINUED. AUTOPLT DISENGAGED AND MANUAL LEVELOFF ACCOMPLISHED AT FL327.

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.

A DC9-30 in cruise at FL330 deviated from the assigned altitude due to the autoplt altitude hold function failure.