Summary
The FAA is revising an earlier proposed airworthiness directive (AD) for all Boeing Model 767 airplanes. The original NPRM would have required the following actions for the drive mechanism of the horizontal stabilizer: Repetitive detailed inspections for discrepancies and loose ball bearings; repetitive lubrication of the ballnut and ballscrew; repetitive measurements of the freeplay between the ballnut and the ballscrew; and corrective action if necessary. The original NPRM resulted from a report of extensive corrosion of a ballscrew in the drive mechanism of the horizontal stabilizer on a similar airplane model. This action revises the original NPRM by including additional initial and repetitive inspections of the ballscrew-to-ballnut freeplay for certain airplanes, and adding a new compliance time for those inspections. We are proposing this supplemental NPRM to prevent an undetected failure of the primary load path for the ballscrew in the drive mechanism of the horizontalstabilizer and subsequent wear and failure of the secondary load path, which could lead to loss of control of the horizontal stabilizer and consequent loss of control of the airplane.