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FM Program: Analysis of Mode Confusion

(Note: most of the following text comes directly from the June 2000 edition of NASA Langley`s Research and Technology-Transfer Program in Formal Methods, which is available in PDF (Download Adobe Acrobat Reader link to external site if needed).

The goal of the NASA Aviation Safety Program is to reduce the civil aviation fatal accident rate by 80% in ten years and 90% in twenty years. This program is being driven by the accident data with a focus on the most recent history. Pilot error is the most commonly cited cause for fatal accidents (up to 70%), and thus is being given major consideration in this program. The January 30, 1995 issue of Aviation Week and Space Technologylists 184 incidents and accidents involving mode awareness including the Bangalore A320 crash (14 February 1990), the trasbourg A320 crash (20 January 1992), the Habsheim A320 crash (26 June 1988), and the Toulouse A330 crash (30 June 1994).

These incidents and accidents reveal that pilots sometimes become confused about what the cockpit automation is doing. Consequently, human factors research is an obvious investment area. However, even a cursory look at the incident and ccident data reveals that the mode confusion problem is much deeper than just training deficiencies and a lack of human-oriented design. This is readily acknowledged by human factors experts. For example, Charles E. Billings, writes in Aviation Automation: The Search for a Human-Centered Approach, 1997 (pg 144):

... today`s flight management systems are "mode rich" and it is often difficult for pilots to keep track of them (see Fig 9.2). The second problem, which is related to the first involves lack of understanding by pilot`s of the system`s internal architecture and logic, and therefore a lack of understanding of what the machine is doing, and why, and what it is going to do next.

Similarly, Sarter and Woods write in Decomposing Automation, 1994:

What is needed is better understanding of how the machine operates, not just how to operate the machine.

It seems that further progress in human factors will only come through a deeper scrutiny of the internals of the automation. Formal methods can contribute in this arena. The fundamental goal of formal methods is to capture requirements, designs, and implementations in a mathematically-based model that can be analyzed in a rigorous manner. By capturing the internal behavior of a flight deck in a rigorous and detailed formal model, the dark corners of a design can be analyzed.

This project is exploring two complementary strategies based on a formal model:

  • Visualization: Create and display a clear, executable formal model of the automation that is easily understood by flight crew and use it to drive the ight deck simulation during training.
  • Analysis: Conduct mathematical analysis of the model and search for mode confusion potential.

For more information, see

  • Ricky W. Butler, Steven P. Miller, James N. Potts, and Victor A. Carreño. A Formal Methods Approach to the Analysis of Mode Confusion. In 17th AIAA/IEEE Digital Avionics Systems Conference, October 31-November 6 1998. (PostScript, PDF)

  • Steven P. Miller and James N. Potts, Detecting Mode Confusion Through Formal Modeling and Analysis, NASA/CR-1999-208971, January 1999, 69 pages. (PDF, compressed PostScript)

  • Steven P. Miller, Alan C. Tribble, Timothy M. Carlson and Eric J. Danielson, ( Flight Guidance System Requirements Specification ) , NASA/CR-2003-212426, June 2003, pp. 176

  • Steven P. Miller, Sarah Barber, Timothy M. Carlson, David L. Lempia, and Alan C. Tribble, A Methodology for Improving Mode Awareness in Flight Guidance Design, in Proceedings of the 21st Digital Avionics Systems Conference (DASC'02), Irvine, California, Oct. 27-31, 2002.

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last modified: 6 August 2001 (14:07:44)