Airworthiness Directives; Fokker Model F28 Mark 1000 Through 4000 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Fokker Model F28 Mark 1000 through 4000 series airplanes, that requires replacing certain flexible hydraulic hoses that connect to the UP-port of the actuator of each main landing gear (MLG) with certain new flexible hoses that have built-in restrictor check-valves. This amendment is prompted by results of tests, which indicate that, for airplanes on which restrictor check-valves are not installed, sudden movement of the actuator of the MLG, which could occur under extreme inward sideload conditions (such as touching down at a large crab angle), may pressurize the downlock-actuator and lift the MLG toggle-links. The actions specified by this AD are intended to prevent such pressurization of the downlock-actuator and consequent lifting of the toggle-links, which could result in collapse of the MLG and reduced controllability of the airplane during landing.