Airworthiness Directives; Boeing Model 757-200 Series Airplanes Modified by Supplemental Type Certificate (STC) SA979NE

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 757-200 series airplanes. This AD requires a one- time deactivation of the auxiliary fuel system, repetitive venting and draining of the auxiliary fuel tank sumps, and revising the Limitations section of the airplane flight manual to limit the maximum cargo weight. This AD results from a re-evaluation of the floor structure and cargo barriers conducted by the STC holder. We are issuing this AD to prevent structural overload of the auxiliary fuel tank support structure, which could cause the floor beams to fail, damaging the primary flight controls and the auxiliary power unit fuel lines that pass through the floor beams, resulting in loss of control of the airplane. We are also issuing this AD to prevent structural overload of the cargo barriers, which could cause the barriers to fail, allowing the cargo to shift, resulting in damage to the auxiliary fuel tanks, residual fuel leakage, and consequent increased risk of a fire.