Page:NTSB Aircraft Accident Report, United Airlines Flight 389.pdf/22

 was in the neutral position. The elevator centering spring assembly was in the center position and could be moved to contact both stops. While the elevator control linkage was damaged, there was no evidence of pre-impact distress or failure. The elevator feel computer and feel control units were functionally tested and met all test requirements. The horizontal stabilizer jackscrew was examined and the "B" dimension between the stops measured at 5-3/4 inches. This is equivalent to 0.5 units of aircraft nose up trim. The stabilizer trim brake assembly was recovered but the drive sprocket, brake release arm and mounting flanges were not recovered. The left hand stabilizer brake stop pawl and attached spring cartridge were found in an overcenter position against the case. This pawl is designed to stop stabilizer movement in the aircraft nose up direction. In this position the pawl was beyond the designed limit of its travel and could not function as a brake or stop device. The stabilizer trim brake system is actuated by operation of either pilot's control column to stop stabilizer out-of-trim motion. Should a runaway stabilizer cause a pitch in an unwanted direction, moving either pilot's control column in the opposite direction will stop the stabilizer from further movement in the out-of-trim direction, but will permit movement in the opposite direction. A measurement was taken of the control stand stabilizer trim jack assembly and 1.7 inches existed between the trunion and the nut assembly. This is equivalent to 1.25 units aircraft nose down. The hydraulic power units of the ailerons, rudder and elevators were recovered and tested. The aileron power control unit passed the functional