IFR training flight autoplt gives hard over signal resulting in upset.

Attributes
ACN	99997
Time
Date	198812
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : adm
State Reference	OK
Altitude	msl bound lower : 1500 msl bound upper : 4000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw
Operator	general aviation : instructional
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	instruction : instructor
Qualification	pilot : commercial pilot : cfi pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 890 flight time type : 25
ASRS Report	99997
Person 2
Affiliation	Other
Function	instruction : trainee
Qualification	pilot : private
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : regained aircraft control other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

We were northbound on 343 degree right off ardmore at 4000'. Turned on autoplt for about 3 mins, then all of sudden were in a 90 degree bank going down at 3000 FPM. Turned autoplt off, pulled power, pulled fuse for autoplt, turned on carburetor heat, lost 80% engine power, took bank out slowly, broke out about 1500' MSL level airplane pitch up to level flight about 300' above ground, got bearing, and turned left to 350 degrees. 3 mi to pauls valley airport. Flew plane with 1200 RPM to airport and landed. I think autoplt on small aircraft should be checked and tested more often. Callback conversation with reporter revealed the following: did not have pitot heat on at time of incident. Gave the aircraft type and autoplt model. Did not feel he had any problem with the static system. Admitted however when in the descent he put the carburetor heat on and knew that was probably the trouble with the engine. Air was extremely smooth, but he was flying in clouds for training for the student working on an instrument rating. When he took the aircraft the student called the center and advised they were in 90 degree bank descending at 3000 FPM. Did not declare emergency or set transponder to 7700. Apparently no loss of sep. Maintenance checked the aircraft over and found no irregularities and flew the aircraft to home base using the autoplt and everything worked perfectly.

Original NASA ASRS Text

Title: IFR TRAINING FLT AUTOPLT GIVES HARD OVER SIGNAL RESULTING IN UPSET.

Narrative: WE WERE NBOUND ON 343 DEG R OFF ARDMORE AT 4000'. TURNED ON AUTOPLT FOR ABOUT 3 MINS, THEN ALL OF SUDDEN WERE IN A 90 DEG BANK GOING DOWN AT 3000 FPM. TURNED AUTOPLT OFF, PULLED PWR, PULLED FUSE FOR AUTOPLT, TURNED ON CARB HEAT, LOST 80% ENG PWR, TOOK BANK OUT SLOWLY, BROKE OUT ABOUT 1500' MSL LEVEL AIRPLANE PITCH UP TO LEVEL FLT ABOUT 300' ABOVE GND, GOT BEARING, AND TURNED LEFT TO 350 DEGS. 3 MI TO PAULS VALLEY ARPT. FLEW PLANE WITH 1200 RPM TO ARPT AND LANDED. I THINK AUTOPLT ON SMA SHOULD BE CHKED AND TESTED MORE OFTEN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: DID NOT HAVE PITOT HEAT ON AT TIME OF INCIDENT. GAVE THE ACFT TYPE AND AUTOPLT MODEL. DID NOT FEEL HE HAD ANY PROB WITH THE STATIC SYS. ADMITTED HOWEVER WHEN IN THE DSCNT HE PUT THE CARB HEAT ON AND KNEW THAT WAS PROBABLY THE TROUBLE WITH THE ENG. AIR WAS EXTREMELY SMOOTH, BUT HE WAS FLYING IN CLOUDS FOR TRNING FOR THE STUDENT WORKING ON AN INSTRUMENT RATING. WHEN HE TOOK THE ACFT THE STUDENT CALLED THE CENTER AND ADVISED THEY WERE IN 90 DEG BANK DSNDING AT 3000 FPM. DID NOT DECLARE EMER OR SET TRANSPONDER TO 7700. APPARENTLY NO LOSS OF SEP. MAINT CHKED THE ACFT OVER AND FOUND NO IRREGULARITIES AND FLEW THE ACFT TO HOME BASE USING THE AUTOPLT AND EVERYTHING WORKED PERFECTLY.

Data retrieved from NASA's ASRS site as of August 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.