Altitude deviation.

Attributes
ACN	156333
Time
Date	199009
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : fmn
State Reference	NM
Altitude	msl bound lower : 19000 msl bound upper : 20700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	general aviation : personal
Make Model Name	Small Transport, Low Wing, 2 Recip Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial pilot : cfi
Experience	flight time last 90 days : 100 flight time total : 1050 flight time type : 100
ASRS Report	156333
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 controllera
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On departure from four corners airport in farmington, NM, we were cleared to FL190. Upon reaching FL190, the autoplt was engaged and altitude hold was selected. I switched on the cabin heater, but no heat was being delivered to the cabin. While consulting the pilot's operating handbook to get the heater working, the autoplt switched itself from altitude hold to attitude hold and the plane began climbing gradually west/O my knowledge. Just as I noticed the deviation, center called and asked me to check my altitude. I descended to the proper altitude and ceased to use the autoplt. Distrs of the inoperative heater caused an excessive amount of reliance on the autoplt which was unreliable.

Original NASA ASRS Text

Title: ALT DEVIATION.

Narrative: ON DEP FROM FOUR CORNERS ARPT IN FARMINGTON, NM, WE WERE CLRED TO FL190. UPON REACHING FL190, THE AUTOPLT WAS ENGAGED AND ALT HOLD WAS SELECTED. I SWITCHED ON THE CABIN HEATER, BUT NO HEAT WAS BEING DELIVERED TO THE CABIN. WHILE CONSULTING THE PLT'S OPERATING HANDBOOK TO GET THE HEATER WORKING, THE AUTOPLT SWITCHED ITSELF FROM ALT HOLD TO ATTITUDE HOLD AND THE PLANE BEGAN CLBING GRADUALLY W/O MY KNOWLEDGE. JUST AS I NOTICED THE DEVIATION, CENTER CALLED AND ASKED ME TO CHK MY ALT. I DSNDED TO THE PROPER ALT AND CEASED TO USE THE AUTOPLT. DISTRS OF THE INOP HEATER CAUSED AN EXCESSIVE AMOUNT OF RELIANCE ON THE AUTOPLT WHICH WAS UNRELIABLE.

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.