Jetstar captain reports automatic pilot malfunction causing altitude overshoot at FL380.

Attributes
ACN	786520
Time
Date	200805
Place
Locale Reference	airport : orf.airport
State Reference	VA
Altitude	msl bound lower : 38000 msl bound upper : 38500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	general aviation : corporate
Make Model Name	Jetstar 1329 (C140)
Operating Under FAR Part	Part 91
Flight Phase	cruise : level cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : multi engine pilot : atp
Experience	flight time last 90 days : 60 flight time total : 6300 flight time type : 700
ASRS Report	786520
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned altitude flight crew : overcame equipment problem
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

We had just leveled off at FL380. The altitude preselect had leveled us about 50 ft low. As the aircraft nudged itself to the correct level; the autoplt suddenly released the altitude mode and climbed at approximately 2000 FPM. I disconnected the autoplt; stopped the climb by FL385; and started back down while telling my copilot to notify ATC of the problem and being corrected. No TA's or RA's were encountered. By the time transmitted to center; we were only 300 ft high and the autoplt was re-engaged and functioning properly. Aircraft leveled at FL380 and performed normally for the remainder of the flight.

Original NASA ASRS Text

Title: JETSTAR CAPT REPORTS AUTO PILOT MALFUNCTION CAUSING ALTITUDE OVERSHOOT AT FL380.

Narrative: WE HAD JUST LEVELED OFF AT FL380. THE ALT PRESELECT HAD LEVELED US ABOUT 50 FT LOW. AS THE ACFT NUDGED ITSELF TO THE CORRECT LEVEL; THE AUTOPLT SUDDENLY RELEASED THE ALT MODE AND CLBED AT APPROX 2000 FPM. I DISCONNECTED THE AUTOPLT; STOPPED THE CLB BY FL385; AND STARTED BACK DOWN WHILE TELLING MY COPLT TO NOTIFY ATC OF THE PROB AND BEING CORRECTED. NO TA'S OR RA'S WERE ENCOUNTERED. BY THE TIME XMITTED TO CTR; WE WERE ONLY 300 FT HIGH AND THE AUTOPLT WAS RE-ENGAGED AND FUNCTIONING PROPERLY. ACFT LEVELED AT FL380 AND PERFORMED NORMALLY FOR THE REMAINDER OF THE FLT.

Data retrieved from NASA's ASRS site as of May 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.