What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
According to the pilots,the following occurred. The aircraft departed fcn at 0815 on 08/15/2012.the intended destination was arlington,TX.prior to departing fcn,the aircraft waited for a thunderstorm to pass and sat in the rain for approximately 45 minutes to 1 hour. After approximately 10 minutes of cruise flight at 40,000 feet (about 35 minutes into the flight),the auto pilot pitch trim mis-compare light illuminated along with associated master caution flasher. The fault was identified and master caution was cancelled. The abnormal checklist was then beginning to be referenced by the co-pilot in the RH seat. The pilot in the LH seat looked down at the auto-pilot annunciator on the center pedestal and noted that the green down light was illuminated. Before any checklist items could be read,the auto-pilot disengaged (on its own) and the plane suddenly nosed down to a 20-25 degree nose down attitude. The airspeed immediately jumped 30-40 knots over red line and the pilot grabbed the control yoke with both hands and attempted to pull the aircraft out of its descent. The throttles were reduced to idle,an emergency was declared with ATC,and the speed brakes were extended. Once the airspeed was reduced to below red line and the aircraft descent had stopped,altitude was now 33,000-34,000 feet. The pilot was using both hands to maintain altitude. The co-pilot used the manual trim wheel to reduce fwd trim pressure. The co-pilot indicated later that the trim wheel was not stuck and felt normal when moving it. The aircraft diverted to the dsm airport.
As the FAA filed it
ACCORDING TO THE PILOTS,THE FOLLOWING OCCURRED. THE AIRCRAFT DEPARTED FCN AT 0815 ON 08/15/2012.THE INTENDED DESTINATION WAS ARLINGTON,TX.PRIOR TO DEPARTING FCN,THE AIRCRAFT WAITED FOR A THUNDERSTORM TO PASS AND SAT IN THE RAIN FOR APPROXIMATELY 45 MINUTES TO 1 HOUR. AFTER APPROXIMATELY 10 MINUTES OF CRUISE FLIGHT AT 40,000 FEET (ABOUT 35 MINUTES INTO THE FLIGHT),THE AUTO PILOT PITCH TRIM MIS-COMPARE LIGHT ILLUMINATED ALONG WITH ASSOCIATED MASTER CAUTION FLASHER.THE FAULT WAS IDENTIFIED AND MASTER CAUTION WAS CANCELLED.THE ABNORMAL CHECKLIST WAS THEN BEGINNING TO BE REFERENCED BY THE CO-PILOT IN THE RH SEAT.THE PILOT IN THE LH SEAT LOOKED DOWN AT THE AUTO-PILOT ANNUNCIATOR ON THE CENTER PEDESTAL AND NOTED THAT THE GREEN DOWN LIGHT WAS ILLUMINATED.BEFORE ANY CHECKLIST ITEMS COULD BE READ,THE AUTO-PILOT DISENGAGED (ON ITS OWN) AND THE PLANE SUDDENLY NOSED DOWN TO A 20-25 DEGREE NOSE DOWN ATTITUDE. THE AIRSPEED IMMEDIATELY JUMPED 30-40 KNOTS OVER RED LINE AND THE PILOT GRABBED THE CONTROL YOKE WITH BOTH HANDS AND ATTEMPTED TO PULL THE AIRCRAFT OUT OF ITS DESCENT.THE THROTTLES WERE REDUCED TO IDLE,AN EMERGENCY WAS DECLARED WITH ATC,AND THE SPEED BRAKES WERE EXTENDED. ONCE THE AIRSPEED WAS REDUCED TO BELOW RED LINE AND THE AIRCRAFT DESCENT HAD STOPPED,ALTITUDE WAS NOW 33,000-34,000 FEET.THE PILOT WAS USING BOTH HANDS TO MAINTAIN ALTITUDE.THE CO-PILOT USED THE MANUAL TRIM WHEEL TO REDUCE FWD TRIM PRESSURE.THE CO-PILOT INDICATED LATER THAT THE TRIM WHEEL WAS NOT STUCK AND FELT NORMAL WHEN MOVING IT.THE AIRCRAFT DIVERTED TO THE DSM AIRPORT.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.