DC9 crew had altitude excursion.

Attributes
ACN	464754
Time
Date	200003
Day	Wed
Local Time Of Day	0601 To 1200
Place
State Reference	MO
Altitude	msl bound lower : 31000 msl bound upper : 31300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zkc.artcc
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 200 flight time total : 2800 flight time type : 300
ASRS Report	464754
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Resolutory Action	flight crew : returned to assigned altitude none taken : detected after the fact
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

At cruise altitude, the autoplt performed an uncommanded pitch up while 'altitude hold' was engaged. The captain recovered the aircraft immediately. The altitude increased momentarily by +300 ft. We monitored the autoplt, with no further deviations.

Original NASA ASRS Text

Title: DC9 CREW HAD ALT EXCURSION.

Narrative: AT CRUISE ALT, THE AUTOPLT PERFORMED AN UNCOMMANDED PITCH UP WHILE 'ALT HOLD' WAS ENGAGED. THE CAPT RECOVERED THE ACFT IMMEDIATELY. THE ALT INCREASED MOMENTARILY BY +300 FT. WE MONITORED THE AUTOPLT, WITH NO FURTHER DEVS.

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.