Airworthiness Directives; Learjet Model 24, 25, 31, 35, 36, and 55 Series Airplanes, and Learjet Model 28 and 29 Airplanes

Abstract

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Learjet Model 24, 25, 31, 35, 36, and 55 series airplanes, and Learjet Model 28 and 29 airplanes. This action requires a revision to the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to prohibit flight above an altitude of 41,000 feet. This action also provides optional terminating action for that AFM revision. This amendment is prompted by a report of failure of a safety valve in the pressurization system on a Learjet Model 31A airplane and reports of cracks found in the poppets of certain outflow/ safety valves due to an improper molding process. The actions specified in this AD are intended to prevent such cracking and subsequent failure of the valves, which could result in rapid decompression of the airplane.