An airplane fuel tank inerting system provides an inert atmosphere in a fuel tank to minimize explosive ignition of fuel vapor. This SAE Aerospace Information Report (AIR) deals with the three methods of fuel tank inerting systems currently used in operational aircraft: (1) on-board inert gas generation systems (OBIGGS), (2) liquid/gaseous nitrogen systems, and (3) halon systems. The OBIGGS and nitrogen systems generally are designed to provide full-time fuel tank fire protection; the halon systems generally are designed to provide only on-demand or combat-specific protection. This document also addresses other design considerations that affect fuel tank flammability such as fuel tank pressure and other methods for reducing fuel tank flammability. This AIR does not treat the subject of explosion suppression foam (ESF) that has been used for fuel tank explosion protection on some military aircraft. ESF is also available for retrofit for commercial airplanes.