Action
Notice of proposed rulemaking (NPRM).
Summary
We propose to supersede an existing airworthiness directive (AD) that applies to certain Learjet Inc. Model 60 airplanes. The existing AD currently requires determining if a certain fuel crossflow tube is installed; and follow-on/corrective actions, as applicable. Since we issued that AD, we have received a report that airplanes produced since 2003 might also be subject to the unsafe condition; and that the minimum allowable clearance is not established in the airplane maintenance information, and therefore, must be addressed by this proposed AD. This proposed AD would retain all actions in the previous AD, and would require determining if a certain fuel crossflow tube is installed, performing repetitive measurements of the fuel crossflow tube and surrounding valves and cables, and doing corrective actions if applicable. In addition, this proposed AD expands the applicability of the existing AD. We are proposing this AD to prevent chafing and consequent failure of the fuel crossflow tube due to inadequate clearance between the tube and the flight control cables, which could result in loss of fuel from one fuel tank during normal operating conditions or loss of fuel from both main fuel tanks during fuel cross- feeding operations.