Summary
We propose to adopt a new airworthiness directive (AD) for the products listed above. This proposed AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as: One operator reported loss of both pitch trims following autopilot disengagement after take off. Subsequent shop findings revealed severe damage to the power gears. Mal-phasing between the hydraulic motors was suspected to have induced excessive loads into the gear train, leading to collapse of one bearing on a shaft of the main gear, causing severe tooth damage. The combination of tooth damage and gear tilting caused the disconnection of two of the three hydraulic motors, resulting in jamming of the THSA [Trimmable Horizontal Stabilizer Actuator] gearbox and consequent loss of THSA control. This condition, if not detected and corrected, could lead to further cases of mal-phasing of the hydraulic motors of the THSA, causing degradation of the power gears and potentially resulting in reduced control of the aeroplane. The proposed AD would require actions that are intended to address the unsafe condition described in the MCAI.