Graham Warwick/ATLANTA
NASA HAS successfully landed a McDonnell Douglas MD-11 using only engine-thrust for flight control. The propulsion-controlled aircraft (PCA) tests at Edwards AFB, California on 29 August follow similar flights in April 1993 with a McDonnell Douglas F-15. Further PCA tests are planned using a McDonnell Douglas C-17.
The MD-11, which was piloted by NASA test pilot Gordon Fullerton, was flown through the autopilot, using modified software in the Honeywell flight-control computers to send thrust commands to the full-authority digital engine-control units on the wing-mounted Pratt & Whitney PW4460s engines.
The autopilot vertical-speed knob was used to command symmetrical thrust changes for longitudinal control, and the heading/bank-angle knob to command differential thrust for lateral control. Engine thrust, nominally 111kN (25,000lb), was varied by up to ±22kN. Response was sluggish, typically 2s, says NASA, but the landings were smooth.
A second series of MD-11 tests is planned for late 1995, to evaluate propulsion-controlled approaches in the clean configuration and coupled to an instrument-landing system, and to look at use of the centre engine for speed control. Simulator testing for the C-17 PCA flights has begun.
NASA's PCA effort follows several incidents in which aircraft have lost flight controls because of hydraulic failures, notably the crash of a United Airlines McDonnell Douglas DC-10 at Sioux City in 1989.
Source: Flight International
