Development and Flight Test of an Emergency Flight Control System Using Only Engine Thrust on an MD-11 Transport Airplane(8)

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After the successful completion of the F-15 PCA research, MDA (Long Beach, California), Pratt & Whitney Aircraft (East Hartford, Connecticut), Honeywell, Inc. (Phoenix, Arizona), and NASA Dryden developed and tested a concept demonstration PCA system for the MD-11 transport airplane. The objectives were to develop a PCA control system, to demonstrate controlled up-and-away .ight over a portion of the .ight envelope from 150 to 250 kn below 15,000 ft, and to make approaches to a runway to 20 ft above ground level (AGL) that could result in a survivable landing, with a sink rate of less than 10 ft/sec and a bank angle of less than 7° and within 50 ft of runway centerline. A goal was to make actual PCA landings. To make the PCA demonstration applicable to the many transports with two wing-mounted engines, the MD-11 PCA system primarily employed only the wing-mounted engines. In addition, control modes that use the added capability of the tail-mounted engine were developed. The PCA system that was developed and tested uses only software changes to existing digital systems on the MD-11.
In more than 25 hr of testing, the PCA system exceeded the objectives, serving as an acceptable autopilot and performing landings without conventional .ight controls (ref. 9). Later tests studied PCA operation over the entire .ight envelope, in upset conditions, with all hydraulic systems turned off, and coupled to an instrument-landing system (ILS) for hands-off landings. Sixteen pilots .ew PCA demonstration .ights (ref. 10). Reference 11 gave an overview of the MD-11 PCA program. Reference 12 gave an analysis of the lateral control system design and performance, reference 13, the longitudinal control system details, and reference 14, details of the hardware architecture, software development, and testing. Reference 15 summarized comments of the project pilot.
This paper presents the following:
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A history of the MD-11 PCA project

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A summary of accidents or incidents in which engine thrust was or could have been used

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The principles of throttles-only .ight control for a subsonic transport

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A description of the MD-11 airplane

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Development of the PCA system for the MD-11

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A description of the control laws

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Flight test results and pilot comments

The chronology of the development and .ight test sequence is preserved to illustrate and document the process used.

HISTORY OF LOSS OF FLIGHT CONTROL ACCIDENTS AND INCIDENTS
Many accidents and incidents have resulted from major .ight control failures in which the crew either did or could have used throttles for emergency .ight control (ref. 1).
B-747, Japan
In 1985, a four-engine Boeing 747 aircraft, Japan Airlines .ight 123, experienced a total hydraulic system loss as a result of a failure in an aft cabin pressure bulkhead. Most of the vertical .n was also lost. After the failure, the aircraft remained essentially trimmed, with persistent dutch roll and phugoid oscillations. The throttles and electrically driven .aps were the only usable devices for control. The B-747 was .own for more than 30 min using throttle control, but the crew was not able to effectively control the airplane and eventually hit a mountain (ref. 16). More than 520 lives were lost.

DC-10, Sioux City, Iowa
In July 1989, a McDonnell Douglas DC-10 trijet, United Airlines .ight 232, in cruise .ight suffered an uncontained tail engine failure that caused the loss of all hydraulics. After the failure, the airplane trimmed at approximately 210 kn with a signi.cant yaw caused by damage to the center-engine nacelle. The crew learned to achieve gross control under extremely dif.cult circumstances using wing engine throttles for control; the right-engine thrust was required to be about twice the left-engine thrust to hold wings level. In spite of these dif.culties, the crew did reach the airport at Sioux City, Iowa. Not enough control precision was available for a safe landing; the phugoid was not well damped. However, an emergency crash landing saved 181 of 296 persons on board (ref. 17).
　
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