Altitude deviation autoplt did not hold altitude.

Attributes
ACN	301970
Time
Date	199504
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : bal
State Reference	MD
Altitude	msl bound lower : 27000 msl bound upper : 27300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 21000 flight time type : 5000
ASRS Report	301970
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 3000
ASRS Report	301029
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
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	Pilot Deviation

Narrative:

We were level at FL270 talking to cle ARTCC approximately XA00 with FL270 in the altitude window. After 4-5 mins, aircraft began climbing through FL272, disengaged autoplt. Stopped climb by 27300 ft and corrected back to FL270. Autoplt worked normally rest of the flight.

Original NASA ASRS Text

Title: ALTDEV AUTOPLT DID NOT HOLD ALT.

Narrative: WE WERE LEVEL AT FL270 TALKING TO CLE ARTCC APPROX XA00 WITH FL270 IN THE ALT WINDOW. AFTER 4-5 MINS, ACFT BEGAN CLBING THROUGH FL272, DISENGAGED AUTOPLT. STOPPED CLB BY 27300 FT AND CORRECTED BACK TO FL270. AUTOPLT WORKED NORMALLY REST OF THE FLT.

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.