From Sioux City to the X-33

The history of the "Propulsion Controlled Aircraft (PCA)" problem is reviewed. While there had been repeated warnings that life-threatening hydraulic failure in a modern airliner can occur despite an estimated probability of 10(-9) only after the Sioux City accident was the possibility of using some automatic fly-by-throttle back up control system for crippled airplane seriously considered. Several different schemes to help pilots fy hydraulically depleted aircraft by using collective and differential thrust of the engines will be reviewed. Special attention win be devoted to the so-called "model matching" methodology. Finally, it will be shown how this research can be extrapolated to the X-33, the reduced scale demonstration vehicle of the new space shuttle. Copyright (C) 1998 IFAC.