Pilot of an aztec 250 has an altitude deviation due to altitude hold malfunctioning and climbs 1000 ...

Attributes
ACN	429147
Time
Date	199902
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : pll.vor
State Reference	IL
Altitude	msl bound lower : 6000 msl bound upper : 7000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : rfd.tracon
Operator	general aviation : personal
Make Model Name	PA-23-250 Aztec
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : multi engine pilot : commercial pilot : cfi
Experience	flight time last 90 days : 110 flight time total : 1100 flight time type : 105
ASRS Report	429147
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to original clearance
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I had leveled at 6000 ft MSL and activated the autoplt. I started to prepare for my arrival and was busy looking at charts and approach plates. I was monitoring my heading, and I thought that I was maintaining my scan, but when I looked up one time to check things, I realized that my airspeed was low. I tried to determine my problem (checked throttle, manifold pressure, and tachometer) and I finally realized I had gained 1000 ft and was at 7000 ft MSL. I looked at my autoplt and realized that the altitude hold had turned off. I immediately started a descent and returned to 6000 ft MSL. Looking back, I realize that I was fatigued at takeoff and I should have concentrated more at maintaining a full instrument scan instead of trusting the autoplt. I also put too much faith in the autoplt, and I realize I need to have a better understanding of all aircraft system, as I expected an auditory warning when the autoplt deactivated itself, and that warning never occurred.

Original NASA ASRS Text

Title: PLT OF AN AZTEC 250 HAS AN ALTDEV DUE TO ALT HOLD MALFUNCTIONING AND CLBS 1000 FT ABOVE ASSIGNED ALT.

Narrative: I HAD LEVELED AT 6000 FT MSL AND ACTIVATED THE AUTOPLT. I STARTED TO PREPARE FOR MY ARR AND WAS BUSY LOOKING AT CHARTS AND APCH PLATES. I WAS MONITORING MY HDG, AND I THOUGHT THAT I WAS MAINTAINING MY SCAN, BUT WHEN I LOOKED UP ONE TIME TO CHK THINGS, I REALIZED THAT MY AIRSPD WAS LOW. I TRIED TO DETERMINE MY PROB (CHKED THROTTLE, MANIFOLD PRESSURE, AND TACHOMETER) AND I FINALLY REALIZED I HAD GAINED 1000 FT AND WAS AT 7000 FT MSL. I LOOKED AT MY AUTOPLT AND REALIZED THAT THE ALT HOLD HAD TURNED OFF. I IMMEDIATELY STARTED A DSCNT AND RETURNED TO 6000 FT MSL. LOOKING BACK, I REALIZE THAT I WAS FATIGUED AT TKOF AND I SHOULD HAVE CONCENTRATED MORE AT MAINTAINING A FULL INST SCAN INSTEAD OF TRUSTING THE AUTOPLT. I ALSO PUT TOO MUCH FAITH IN THE AUTOPLT, AND I REALIZE I NEED TO HAVE A BETTER UNDERSTANDING OF ALL ACFT SYS, AS I EXPECTED AN AUDITORY WARNING WHEN THE AUTOPLT DEACTIVATED ITSELF, AND THAT WARNING NEVER OCCURRED.

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.

Pilot of an aztec 250 has an altitude deviation due to altitude hold malfunctioning and climbs 1000 ft above assigned altitude.