A pilot reports difficulty with an autoplt climbing above assigned altitude near gqe.

Attributes
ACN	453440
Time
Date	199911
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : gqe.vor
State Reference	TN
Altitude	msl bound lower : 7000 msl bound upper : 7300
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zme.artcc
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Operating Under FAR Part	Part 91
Navigation In Use	other other vortac
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : multi engine pilot : commercial
Experience	flight time last 90 days : 75 flight time total : 1900 flight time type : 230
ASRS Report	453440
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I have had numerous unpredictable and inadvertent problems in a/south kap-140 autoplt. Problem #1: without warning or any display change, autoplt will initiate a subtle climb. This problem appears to be aggravated by turbulence of any kind. Problem #2: on descent and approachs, a programmed descent will be started as designed but will be altered by the autoplt during the execution, ie, program for a descent at 5000 FPM which is displayed, will actually be 200-300 ft less. On nov/xa/99, this autoplt initiated one of these unwanted climbs after being stable at 7000 ft for 2 hours or more. The change in altitude was subtle until I detected the plane retrim. I tried to retrim the plane, but it trimmed against me rapidly and I had to disconnect autoplt and retrim. I deviated 200-300 ft from assigned altitude of 7000 ft. I reset the autoplt and all was well. Later in same flight, I programmed for 500 FPM descent that resulted in only about 1/2 that. This autoplt is a replacement for a similar one with same problems. This autoplt increases the workload and in my opinion is of questionable reliability and quality. Autoplt needs to be upgraded or placarded as deficient for precise control.

Original NASA ASRS Text

Title: A PLT RPTS DIFFICULTY WITH AN AUTOPLT CLBING ABOVE ASSIGNED ALT NEAR GQE.

Narrative: I HAVE HAD NUMEROUS UNPREDICTABLE AND INADVERTENT PROBS IN A/S KAP-140 AUTOPLT. PROB #1: WITHOUT WARNING OR ANY DISPLAY CHANGE, AUTOPLT WILL INITIATE A SUBTLE CLB. THIS PROB APPEARS TO BE AGGRAVATED BY TURB OF ANY KIND. PROB #2: ON DSCNT AND APCHS, A PROGRAMMED DSCNT WILL BE STARTED AS DESIGNED BUT WILL BE ALTERED BY THE AUTOPLT DURING THE EXECUTION, IE, PROGRAM FOR A DSCNT AT 5000 FPM WHICH IS DISPLAYED, WILL ACTUALLY BE 200-300 FT LESS. ON NOV/XA/99, THIS AUTOPLT INITIATED ONE OF THESE UNWANTED CLBS AFTER BEING STABLE AT 7000 FT FOR 2 HRS OR MORE. THE CHANGE IN ALT WAS SUBTLE UNTIL I DETECTED THE PLANE RETRIM. I TRIED TO RETRIM THE PLANE, BUT IT TRIMMED AGAINST ME RAPIDLY AND I HAD TO DISCONNECT AUTOPLT AND RETRIM. I DEVIATED 200-300 FT FROM ASSIGNED ALT OF 7000 FT. I RESET THE AUTOPLT AND ALL WAS WELL. LATER IN SAME FLT, I PROGRAMMED FOR 500 FPM DSCNT THAT RESULTED IN ONLY ABOUT 1/2 THAT. THIS AUTOPLT IS A REPLACEMENT FOR A SIMILAR ONE WITH SAME PROBS. THIS AUTOPLT INCREASES THE WORKLOAD AND IN MY OPINION IS OF QUESTIONABLE RELIABILITY AND QUALITY. AUTOPLT NEEDS TO BE UPGRADED OR PLACARDED AS DEFICIENT FOR PRECISE CTL.

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.