Aircraft equipment problem. Autoplt pitch over.

Attributes
ACN	307090
Time
Date	199506
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : atl
State Reference	GA
Altitude	msl bound lower : 14700 msl bound upper : 15000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
Operator	general aviation : personal
Make Model Name	PA-31 Navajo Chieftan/Mojave/Navajo T1020
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Route In Use	enroute airway : ztl
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument pilot : cfi
Experience	flight time last 90 days : 50 flight time total : 3200 flight time type : 150
ASRS Report	307090
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While in cruise with autoplt engaged, plane made a dive. I pulled up and controller asked my altitude. I told her 15000 ft which was correct. I am not sure if an altitude violation occurred but decided to report anyway. Callback conversation with reporter revealed the following: reporter says that the autoplt is presently in the shop being checked. It is an allied signal bendix system. The autoplt was on, but not the altitude hold. The reporter was using the heading bug when suddenly he felt the elevator trim wheel spinning nose down. He disconnected the autoplt and returned the aircraft to assigned altitude.

Original NASA ASRS Text

Title: ACFT EQUIP PROB. AUTOPLT PITCH OVER.

Narrative: WHILE IN CRUISE WITH AUTOPLT ENGAGED, PLANE MADE A DIVE. I PULLED UP AND CTLR ASKED MY ALT. I TOLD HER 15000 FT WHICH WAS CORRECT. I AM NOT SURE IF AN ALT VIOLATION OCCURRED BUT DECIDED TO RPT ANYWAY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR SAYS THAT THE AUTOPLT IS PRESENTLY IN THE SHOP BEING CHKED. IT IS AN ALLIED SIGNAL BENDIX SYS. THE AUTOPLT WAS ON, BUT NOT THE ALT HOLD. THE RPTR WAS USING THE HDG BUG WHEN SUDDENLY HE FELT THE ELEVATOR TRIM WHEEL SPINNING NOSE DOWN. HE DISCONNECTED THE AUTOPLT AND RETURNED THE ACFT TO ASSIGNED ALT.

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.