Cpr light transport cruising on autoplt suddenly pitched up causing an altitude excursion.

Attributes
ACN	299596
Time
Date	199503
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : bzm
State Reference	NC
Altitude	msl bound lower : 25000 msl bound upper : 25300
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : ztl artcc : zau
Operator	general aviation : corporate
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : instrument
Experience	flight time last 90 days : 90 flight time total : 8050 flight time type : 6607
ASRS Report	299596
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

At cruise at FL250, with aircraft on autoplt, and airspeed indicator showing more than 20 KTS below red line, suddenly aircraft pitched up. (A problem with the autoplt?) by the time I disengaged the autoplt, the aircraft had climbed around 300 ft. I descended back to FL250 and reengaged the autoplt and experienced no further problems for the remainder of the flight. After landing the discrepancy was written up in the maintenance logbook.

Original NASA ASRS Text

Title: CPR LTT CRUISING ON AUTOPLT SUDDENLY PITCHED UP CAUSING AN ALT EXCURSION.

Narrative: AT CRUISE AT FL250, WITH ACFT ON AUTOPLT, AND AIRSPD INDICATOR SHOWING MORE THAN 20 KTS BELOW RED LINE, SUDDENLY ACFT PITCHED UP. (A PROB WITH THE AUTOPLT?) BY THE TIME I DISENGAGED THE AUTOPLT, THE ACFT HAD CLBED AROUND 300 FT. I DSNDED BACK TO FL250 AND REENGAGED THE AUTOPLT AND EXPERIENCED NO FURTHER PROBS FOR THE REMAINDER OF THE FLT. AFTER LNDG THE DISCREPANCY WAS WRITTEN UP IN THE MAINT 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.