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The pilot of the Beechcraft King Air reported that just prior to touchdown, the elevator control forces changed abruptly, causing an uncommanded pitch down. The nosewheel struck the surface of the airstrip and the aircraft bounced twice. During the subsequent landing roll, the nose landing gear collapsed and the propellers struck the ground.

An investigation by the operator found that an elevator servo in the autopilot system was malfunctioning. The unit would not disengage when the autopilot was turned off. The mode in which the servo operated on the test bench was consistent with the control forces experienced by the pilot during the landing. Because of the aircraft's proximity to the ground, the pilot had been unable to counter the unexpected forces in time to prevent the nosewheel from striking the ground prematurely.

A manufacturer's product improvement service bulletin, issued soon after the aircraft was manufactured, had not been implemented on this servo unit. The modification was to improve the mechanical integrity of the engage clutch assembly and eliminate the possibility of the clutch not disengaging due to mechanical interference between various parts of the clutch assembly and the servo casting.

The operator forwarded its investigation report to BASI and the Civil Aviation Safety Authority and recommended that the Service Bulletin be upgraded to ensure that all servos of the type still in service were modified.

The Civil Aviation Safety Authority informed BASI that it believes that the occurrence was an isolated incident involving this model servo unit and accordingly, airworthiness directive action is not considered to be warranted at this time.

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