 NASA and McDonnell Douglas researchers are developing and testing ideas to make aircraft safer. Using NASA's F-15 test vehicle, Propulsion Controlled Aircraft Software, or PCA Software, is being tested at NASA's Dryden Flight Research Facility. If the complete hydraulic system on an aircraft fails, the PCA software takes over, providing enough engine control power to steer and safely land the vehicle. Until this breakthrough, a complete hydraulic failure basically rendered a normal aircraft uncontrollable. Here's how the PCA software works. The Propulsion Controlled Aircraft, or PCA system, uses a mixture of common sensor signals and the pilot's pitch and roll commands to adjust the throttles and keep the plane on course. The software generates collective or equal throttle commands for the engines. Without this PCA system, throttle-only control is virtually impossible on an aircraft. Here, the pilot is trying to maintain a steady approach by manually controlling the throttles. Now, with the PCA system on, the aircraft is steadied and is actually taken to a safe touchdown at Dryden, April 21, 1993, without using conventional flight controls. Piloted real-time MD-11 simulations incorporating this PCA technology are currently underway. These tests show that with a PCA system installed, the simulated MD-11 commercial aircraft can be safely landed without conventional flight controls. This will be invaluable on military and commercial aircraft of the future. NASA and the aviation industry will continue to work towards a safer, more controllable aircraft in the future. PCA technology is just one example of today's work towards reaching that goal.