A MERLIN III. AT 4000 FT THE CREW DISCOVERED NO AUTOPLT CTL TO LEVEL THE ACFT WHEN SUDDENLY THE ACFT WENT INTO AN EXTREME NOSE OVER DIVE.

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ON JUNE THU; 2000; I WAS ACCOMPANYING MR. XXX WVWV ON A FLT FROM MURFREESBORO; TN TO ROCKFORD; IL WHEN A MALFUNCTION OF THE AUTOPLT TRIM SYSTEM OCCURRED. WE WERE FLYING IN HIS NEWLY PURCHASED MERLIN IIIA. HE HAD JUST TAKEN DELIVERY OF THIS ACFT THE PREVIOUS WEEK. MR. XXX WVWV HAD RECEIVED HIS INITIAL FLT TRAINING FROM ABC CDE SEVERAL MONTHS PREVIOUS TO THIS INCIDENT AND I WAS ACCOMPANYING HIM TO GIVE HIM ADDITIONAL TRAINING. THE PURPOSE OF THIS TRIP WAS TO FLY TO ROCKFORD AND CORRECT SOME MISS RIGGING THAT I NOTED WHEN THE PWR LEVERS WERE MOVED FROM FLT IDLE TOWARD REVERSE AFTER LNDG THE ACFT. WE WERE CLEARED TO AN ASSIGNED ALT AND UPON REACHING THAT ALT; I NOTED AND COMMENTED TO HIM THAT WE HAD NOT LEVELED OFF. XXX WVWV WHO WAS CONTROLLING THE ACFT WITH THE AUTOPLT; STATED THAT SOMETHING WAS WRONG AND THE THAT THE ACFT WAS NOT RESPONDING TO HIS COMMAND. SUDDENLY; THE ACFT WENT INTO AN EXTREME NOSE OVER DIVE AND I EXPERIENCED EXTREME PRESSURE AGAINST MY SEAT BELT. I GRABBED MY CTL WHEEL AND ATTEMPTED TO DISENGAGE THE AUTOPLT BUT WAS UNABLE TO DO SO. I HAD BOTH HANDS ON THE CTL WHEEL AND EXERTED EVERY BIT OF STRENGTH I COULD MUSTER TO PULL THE ACFT OUT OF ITS DIVE. AT THIS POINT; I AM NOT SURE IF IT WAS XXX WVWV OR MYSELF THAT WAS ABLE TO DISCONNECT THE NONESSENTIAL BUS; BUT IN ANY CASE; IT WAS DISCONNECTED AND WE FINALLY GAINED CTL OF THE ACFT. ONCE CTL HAD BEEN REESTABLISHED; WE REQUESTED A RETURN TO MURFREESBORO FOR LNDG. THE RETURN AND LNDG WERE UNEVENTFUL. WE RECEIVED A FERRY PERMIT; DISABLED THE AUTOPLT; AND FLEW THE ACFT TO MAINT. THIS WHOLE EPISODE TOOK ONLY A FEW SECONDS. I WAS INFORMED LATER THAT THE RADAR TRACK INDICATED THAT WE LOST 600 FT IN 3 SECONDS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE HARD OVER NOSE DIVE AND INABILITY TO DISCONNECT WAS AN ELECTRONIC FAILURE IN THE AUTOPLT AND STABILITY AUGMENTATION SYSTEM. THE RPTR SAID THE ONLY METHOD TO GET THIS SYSTEM TO DISCONNECT WAS PULLING THE NONESSENTIAL BUS CIRCUIT BREAKER WHICH PWRS THIS SYSTEM. THE RPTR SAID BOTH CREW MEMBERS PULLED WITH FULL STRENGTH ON THE CTL WHEEL BUT PULLING THE CIRCUIT BREAKER SAVED THEIR LIVES. THE RPTR STATED THE AIRPLANE WAS STORED FOR A LONG PERIOD OF TIME BEFORE BEING SOLD TO MR. WVWV.