LOSS OF ACFT CTL IN A CESSNA CITATION-750.

Narrative

DURING AUTOPLT DEVELOPMENTAL FLT TEST A SIMULATED PITCH TRIM RUNAWAY WAS INJECTED. DESIRED RESULT WAS AUTOPLT MONITOR'S TRIP OFF AUTOPLT OR CREW COULD DISCONNECT RUNAWAY. HOWEVER DURING THIS TEST PITCH TRIM RAN FULL NOSE DOWN AND CREW WAS UNABLE TO RECOVER UNTIL FL231. DECLARED AN EMER (DUE TO EXCEEDING VMO BY 10 PERCENT) AND LANDED AT DVT WITHOUT INCIDENT. PROB RESOLUTION LIES IN HOW WE CONDUCT TEST RELATIVE TO INJECTION POINT AND DISCONNECT METHODOLOGIES. CORRECTED! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE ACFT WAS A CESSNA CITATION-750; NOT AS YET CERTIFIED AND THEREFORE CLASSIFIED AS 'EXPERIMENTAL.' THE PURPOSE OF THE TEST WAS TO CHK THE AUTO TRIP FUNCTION OF THE AUTOPLT WHEN IT SENSES A PITCH TRIM RUNAWAY. THIS PITCH TRIM ANOMALY WAS 'INTRODUCED' BY THE ENGINEER SITTING IN THE AFT CABIN; THROUGH HIS KEYBOARD AND COMPUTER. WHEN THE SEVERE NOSE DOWN SIGNAL WAS SENT; THE ACFT PITCHED OVER VIOLENTLY; THROWING THAT ENGINEER AGAINST HIS SEAT BELT AND IMPACTING THE KEYBOARD. THAT MOTION; UNFORTUNATELY; SENT A 'LOCKED' SIGNAL TO THE TRIM DISCONNECT/TRANSFER SYS. THE CREW SPENT THEIR TIME IN THE ENSUING DSCNT ATTEMPTING TO GET TO THE SECONDARY TRIM SYS VIA A GUARDED SWITCH ON THE CONSOLE. THE DESIGN OF THE AUTOPLT SENSING SYS IS SUPPOSED TO HAVE THE AUTOPLT DETECT THIS RUNAWAY SIGNAL TO THE #1 SYS AND AUTO TRANSFER THE AUTOPLT TO THE #2 SYS. THE 'KEYBOARD LOCK' SHUT OUT THIS TRANSFER WHICH; IT CAN BE NOTED; WAS RATHER LATE IN PERFORMING ITS DESIGNED FUNCTION. RPTR STATED THAT THERE WAS A SOFTWARE PROB. THE ACFT NOW HAS A 'KILL' SWITCH IN THE COCKPIT TO PREVENT A 'LOCKED' SIGNAL FROM OVERRIDING ANY AUTO-TRANSFER OR DISCONNECT SIGNALS BY THE PLTS.