Flight crew turned off transponder.

Attributes
ACN	291976
Time
Date	199412
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : cvg
State Reference	OH
Altitude	msl bound lower : 21600 msl bound upper : 22000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	common carrier : air taxi
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 135
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 180 flight time total : 5500 flight time type : 600
ASRS Report	291976
Person 2
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude altitude deviation : crossing restriction not met non adherence : far
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

During cruise flight en route from rzt to pah at 22000 ft MSL, the autoplt hold failed and started trimming nose down and the aircraft lost 400 ft before the crew could recover to level flight at 22000 ft MSL. When the failure occurred, I turned the transponder to stand-by and disconnected the autoplt and recovered to level cruise flight. ATC didn't say anything about the incident.

Original NASA ASRS Text

Title: FLC TURNED OFF XPONDER.

Narrative: DURING CRUISE FLT ENRTE FROM RZT TO PAH AT 22000 FT MSL, THE AUTOPLT HOLD FAILED AND STARTED TRIMMING NOSE DOWN AND THE ACFT LOST 400 FT BEFORE THE CREW COULD RECOVER TO LEVEL FLT AT 22000 FT MSL. WHEN THE FAILURE OCCURRED, I TURNED THE XPONDER TO STAND-BY AND DISCONNECTED THE AUTOPLT AND RECOVERED TO LEVEL CRUISE FLT. ATC DIDN'T SAY ANYTHING ABOUT THE INCIDENT.

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.