Corporate aircraft has autoplt disconnect uncommanded.

Attributes
ACN	320250
Time
Date	199511
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : dro
State Reference	CO
Altitude	msl bound lower : 18000 msl bound upper : 18500
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zdv tower : mgm
Operator	general aviation : corporate
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : atp
Experience	flight time last 90 days : 140 flight time total : 6150 flight time type : 2000
ASRS Report	320250
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	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
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

In cruise flight with autoplt on with 'heading select and altitude hold' on. The autoplt disconnected uncommanded and the aircraft started a slow climb. I caught it at 18300 ft indicated with altimeter set at 29.92. Center called after I corrected my altitude to FL180, and asked if I was having any problems, that he showed my altitude to be up to 18500 ft. I told him no problems but I had climbed to 18300 ft and since then had corrected.

Original NASA ASRS Text

Title: CORPORATE ACFT HAS AUTOPLT DISCONNECT UNCOMMANDED.

Narrative: IN CRUISE FLT WITH AUTOPLT ON WITH 'HDG SELECT AND ALT HOLD' ON. THE AUTOPLT DISCONNECTED UNCOMMANDED AND THE ACFT STARTED A SLOW CLB. I CAUGHT IT AT 18300 FT INDICATED WITH ALTIMETER SET AT 29.92. CTR CALLED AFTER I CORRECTED MY ALT TO FL180, AND ASKED IF I WAS HAVING ANY PROBS, THAT HE SHOWED MY ALT TO BE UP TO 18500 FT. I TOLD HIM NO PROBS BUT I HAD CLBED TO 18300 FT AND SINCE THEN HAD CORRECTED.

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.