Recent developments in aircraft emergency power

Aircraft have become increasingly dependent on uninterrupted electric and hydraulic power for flight control. Aircraft have also become increasingly dependent on shaft power to assist with engine starting in the event of a flameout. The use of turbofan engines, fly-by-wire flight control systems, and less stable aircraft configurations has increased the need for emergency power systems. Several configurations of aircraft emergency power systems are currently in use. These include ram air turbines, bleed air driven power units and propellant power systems. The propellant power systems include stand-alone emergency power systems, emergency engine start systems, and integrated auxiliary and emergency power systems. Two fuels are currently used in emergency power systems: H-70 monopropellant and jet fuel and air bipropellant. H-70 systems are small and lightweight and have been used for many years. However, H-70 is toxic and requires special handling. Jet fuel and air are less toxic and easier to handle. Jet fuel and air bipropellant systems have been used in several emergency power applications. Four aircraft emergency power systems are described: the F-16 emergency power unit; the U-2 emergency start system; The F-2 emergency power system; and the F-22, integrated auxiliary and emergency power system.