Fitts Critical Incident Study

Background

  • During and follwing World War II there were many aircraft accidents involving misinterpretation and misuse of controls. Determining the the details that led up to these accidents was problemmatic do to the subsequent loss of the flight crews.

  • Two Studies were conducted by Fitts and Jones to determine possible circumstances and interventions that led up to these accidents involving aircraft controls and displays.

    • Control Error Study

    Reference: Fitts, P., Jones, R., Analysis of Factors Contributing to 460 "pilot-error" Experiences in Operating Aircraft Controls. Memorandum Reported TSEAA-694-12, Aero Medical Laboratory, Air Material Command, WPAFB, Dayton OH, July 1947.

    Study Hypothesis

    It should be possible to eliminate a large proportion of so-called "pilot-error" accidents by designing equipment in accordance with human requirements.

    Study method

  • In order to determine methods of designing and locating aircraft controls so as to improve pilot efficiency and reduce the frequency of accidents, accounts of 460 errors made in operating controls have been collected and analyzed.

  • Question: Describe in detail an error in operation of a cockpit control (flight control, engine control, toggle switch, selector switch, trim tab, etc.) which was made by yourself or by another person whom you were watching at the time.
  • To minimize personal opinions, only detailed factual information from eyewitness accounts or persons making errors were accepted.
  • The resulting data were only released in aggragate form in which individual flight crew members could not be identified. Flight crew members were assured that that they would not be singled out for disciplinary action as a result of their responses to insure their full cooporation.

    Study Findings

    1. Substitution errors: confusing one control with another, or failing to identify a control when it is needed.
    2. Adjustment errors: operating a control too slowly or too rapidly, moving a switch to the wrong position, or following the wrong sequence in operating several controls.
    3. Forgetting errors: failing to check, unlock, or use a control at the proper time
    4. Reversal errors: Moving a control in a direction opposite to the necessary to produce a desired result
    5. Unintentional activation: inadvertently operating a control without being aware of it
    6. Unable to reach a control: accident or near-accident resulting from "putting head in cockpit" to grasp a control, or inability to reach a control at all

    • Display Error Study

    Reference: Fitts, P., Jones, R. Psychological Aspects of Instrument Display. I:-Analysis of 270 "Pilot-error" Experiences in Reading and Interpreting Aircraft Instruments. Memorandum Report TSEAA-694-12, Aero Medical Laboratory, Air Material Command, Wright-Patterson Air Force Base, Dayton, OH, July 1, 1947. in Sinaiko, W. (ed.).

    Study Hypothesis

    Study method

  • In order to determine methods of designing aircraft instruments so as to improve pilot efficiency and reduce the frequency of accidents, accounts of 270 errors made by pilots in reading and interpreting instruments have been collected and analyzed.
  • Question: Describe in detail some error which you have made in reading or interpreting an aircraft instrument, detecting a signal, or understanding instructions; or describe such an error made by another individual whom you were watching at the time.
  • To minimize personal opinions, only detailed factual information from eyewitness accounts or persons making errors were accepted.
  • The resulting data were only released in aggragate form in which individual flight crew members could not be identified. Flight crew members were assured that that they would not be singled out for disciplinary action as a result of their responses to insure their full cooporation.
  • Results based only factual information

    Study Results

    1. Errors in interpreting multirevolution instrument indications: difficulty in synthesizing information presented by two or more pointers or by a pointer and a rotating dial viewed through a "window"
    2. Reversal errors reversing the interpretation of an instrument indications with the result that subsequent actions aggravate rather than correct an undesirable condition
    3. Signal interpretation errors: misunderstanding the message conveyed by hand signals or by warning horns or lights; difficulties encountered in the interpretation of radio range signals
    4. Legibility errors: errors, usually of small value, which result from difficulty in seeing the numbers or scale on a dial distinctly enough to read the indication properly
    5. Substitution errors: mistaking one instrument for another, confusing which engine is referred to by a pointer of a dual indicating instrument, or failing to locate an instrument when needed.
    6. Using an instrument that is inoperative: accepting as valid the indication of an instrument which is inoperative or operating improperly
    7. Scale interpretation errors: errors which result from difficulty in interpolating between numbered graduations of scale or failure to interpret a number correctly
    8. Errors due to illusions: misconceptions of attitude which arise because of conflict between body sensations and instrument indications; errors due to illusions which occur during the existence of instrument or marginal weather conditions.
    9. Forgetting errors: failing to check or refer properly to an instrument before take-off or during flight

    • Other Applications

    1. Medical work
    2. Laboratory worker
    3. Vehicle operation
    4. Manufacturing
    5. Computer users
    6. ATM machines
    7. Online shopping/orders
    8. Mobile phone use
    9. Kitchen appliances