Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Fokker Model F28 Mark 0100 series airplanes. This proposal would require loosening certain nuts on the horizontal stabilizer control unit (HSCU) to reduce stress on bolts; a one-time inspection of certain bolts on the HSCU to detect cracking, and replacement, if necessary; application of corrosion protection to these bolts; and reassembly and reidentification of the modified HSCU. This proposal is prompted by reports indicating that stress corrosion, resulting from overtightening of nuts on these bolts, has caused some of these bolts to crack and fail. The actions specified by the proposed AD are intended to prevent failure of these bolts because of stress corrosion cracking which, if not corrected, could lead to loss of control of the horizontal stabilizer and reduced controllability of the airplane.