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News from the National Academies
Date: March 4, 1997
Contacts: Molly Galvin, Media Relations Associate
Becky Habel, Media Relations Assistant
(202) 334-2138; Internet <>


More Effort Needed to Avoid Problems
Associated With New Flight Control Systems

WASHINGTON -- More targeted aircraft testing and simulation should be conducted to uncover design characteristics in new flight control systems that -- in rare circumstances -- may mislead pilots and result in unstable or dangerous flight conditions, says a new report* by a National Research Council committee. In addition, pilots and other personnel involved in aircraft design and operation need more training to prevent these situations and to provide greater awareness that they can occur.

These major mismatches in how a pilot expects an aircraft to fly and how it actually responds generally occur when a pilot must act quickly and aggressively to correct an unexpected aircraft motion during a difficult maneuver -- such as a complicated landing pattern -- accompanied by sudden gusts of wind, unexpected traffic conflicts, or other circumstances that require a pilot's immediate attention. If the aircraft does not immediately react as expected to the pilot's commands, the pilot may feel pressure to take other actions that unintentionally make the problem worse. For example, the plane may begin to move up and down in a severe wavelike pattern. This can make it almost impossible for the pilot to control the aircraft with the precision needed.

"Advanced technology has led to better and safer aircraft designs, and problems between pilots and the computers that help them fly are extremely unusual," said committee chair Duane McRuer, chairman of Systems Technology Inc. in Hawthorne, Calif. "However, these problems -- which have resulted in serious accidents for military aircraft -- may also be experienced by commercial pilots. We need to focus attention on such problems and reduce the likelihood that they will occur, especially as more complex technologies are introduced into the design of modern aircraft."

Although it is difficult to pinpoint a cause for these types of events, the majority of them result from design characteristics of the aircraft, particularly the flight control system, that tend to mislead or confuse pilots, the committee said. For example, automatic shifting between modes in a flight control system may change the plane's dynamics in such a way that the pilot cannot always predict how the plane will respond to commands, especially in adverse conditions. Designs must be thoroughly analyzed and tested to ensure that pilots will be able to understand the operation of the aircraft and its flight control system well enough to make sound decisions during both routine operations and emergency situations.

Occurrences are Uncommon

Incidents that result from poor interaction between pilots and advanced flight control systems are unusual even for military and test aircraft, where pilots may be required to perform risky and complicated maneuvers with unproven technologies. Such problems are rarer still for commercial aircraft, which strive for smooth operations and use technologies that have been thoroughly tested. However, commercial airlines may report fewer problems because pilots and accident investigators lack the information and training to identify these events. Some accidents that have been attributed mainly to pilot error alone may actually have occurred because of flight control design features that confused pilots, the committee said. The flight data recorders used on most airliners are not sophisticated enough to report the type of information that is often necessary to confirm or rule out such incidents.

These types of problems may become more difficult to prevent as more aircraft adopt "fly-by-wire" computerized flight control systems and other complex new technologies, the committee said. While advanced technologies offer improvements in aircraft performance, the complexity of these systems makes it difficult for designers to anticipate all of the possible interactions between pilots and their flight control systems -- especially under the rare circumstances that trigger aircraft accidents -- and identify potential problems.

A structured approach for evaluating all aircraft -- both civilian and military -- to reduce the potential of miscommunication between pilots and flight control systems should be an essential part of vehicle design and development, the committee said. Evaluations should continue while a newly designed aircraft is being certified as flightworthy and after the plane is in operation. As commercial airlines begin using more advanced flight data recorders, their capabilities should be expanded to collect data needed for detecting these events. This information should be analyzed routinely by airlines to identify new problems before they cause accidents.

Neither the Federal Aviation Administration nor the military require aircraft manufacturers to conduct specific tests that would definitively assess the potential for problems between the pilot and the flight control system. The approaches used now by both military and civilian aircraft manufacturers are not consistent, and evaluation results are often treated as proprietary information. Top managers involved in aircraft development must be committed to finding and fixing these problems, the committee said, and a free exchange of information should be encouraged throughout the entire aviation community.

As part of a concerted evaluation process, teams of experts in disciplines including flight control, piloting, aerodynamics, and flight dynamics should specify criteria, design processes, and assessment and test procedures for examining possible problems in aircraft response and flight control systems. Research is needed to develop more accurate and broadly applicable criteria for assessing all aircraft, the committee said.

Simulation and Training

More rigorous computer simulations and flight testing also should be performed, the committee said. Pilots of differing skill levels should be involved and assigned appropriate tasks -- for example, landing under stressful conditions that may trigger an adverse event. During the development of new aircraft, test pilots also should be allowed to conduct unstructured test flights to perform various types and combinations of maneuvers as they search for design characteristics that may lead to harmful situations.

Pilots, aircraft designers, and accident investigators need specialized training to be able to identify these events, the committee said. Many pilots have a tendency to blame themselves for problems that arise with control systems, which may explain why so few technical deficiencies are reported by commercial pilots. Pilots should be encouraged to make greater use of systems that allow them to report unusual events without being penalized or punished.

The study was funded by NASA. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides independent advice on science and technology issues under a congressional charter. A committee roster follows.

*Copies of Aviation Safety and Pilot Control: Understanding and Preventing Unfavorable Pilot-Vehicle Interactions are available from the National Academy Press at the mailing address in the letterhead; tel. (202) 334-3313 or 1-800-624-6242. The cost of the report is $37.00 (prepaid) plus shipping charges of $4.00 for the first copy and $.50 for each additional copy. Reporters may obtain copies from the Office of News and Public Information at the letterhead address (contacts listed above).

      Commission on Engineering and Technical Systems
      Aeronautics and Space Engineering Board

      Aviation Safety and Pilot Control:
      Understanding and Preventing Unfavorable Pilot-Vehicle Interactions

      Study Committee

      Duane T. McRuer* (chair)
      Systems Technology Inc.
      Manhattan Beach, Calif.

      Carl S. Droste
      Engineering Manager
      Flight Control Systems Section
      Lockheed Martin Tactical Aircraft Systems
      Fort Worth, Texas

      R. John Hansman Jr.
      Department of Aeronautics and Astronautics
      Massachusetts Institute of Technology

      Ronald A. Hess
      Department of Mechanical and Aeronautical Engineering
      College of Engineering
      University of California

      David P. LeMaster
      Chief, Flight Control Division
      Wright Laboratory
      Wright-Patterson Air Force Base

      Stuart Matthews
      President and CEO
      Flight Safety Foundation
      Alexandria, Va.

      William W. Melvin
      Senior Pilot
      Delta Airlines (retired)
      Denison, Texas

      John D. McDonnell
      Director, Advanced Aircraft Systems
      Advanced Transport Aircraft Development
      McDonnell Douglas Aerospace
      Long Beach, Calif.

      James McWha
      Chief Engineer, Flight Systems
      Boeing Commercial Airplane Group
      Everett, Wash.

      Richard W. Pew
      Principal Scientist and Manager
      Cognitive Sciences and Systems Department
      Bolt Beranek and Newman Inc.
      Cambridge, Mass.


      Alan Angleman
      Study Director

      JoAnn Clayton-Townsend
      Board Director

      (*) Member, National Academy of Engineering