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A HUMAN FACTORS APPROACH TO ACCIDENT ANALYSIS AND
PREVENTION
Scott Shappell, Ph.D. FAA/Civil Aerospace Medical
Institute
Douglas Wiegmann, Ph.D. University of Illinois
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All NAVY/MARINE Class A, B, C Mishaps
Shappell, S. and Wiegmann, D. (1996). U.S. Naval
aviation mishaps 1977-1992 Differences between
single and dual-piloted aircraft. Aviation,
Space, and Environmental Medicine, 67, 65-69.
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Breakdown of a Productive System

• Active Conditions
• Failed to scan instruments
• Penetrated IMC when VFR only

Failed or Absent Defenses
Adapted from Reason (1990)
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Breakdown of a Productive System

• Active and Latent Conditions
• Poor CRM
• Loss of situational awareness

Preconditions for Unsafe Acts
Unsafe Acts

• Active Conditions
• Failed to scan instruments
• Penetrated IMC when VFR only

Failed or Absent Defenses
Adapted from Reason (1990)
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Breakdown of a Productive System

• Latent Conditions
• Deficient training program
• Improper crew pairing

Unsafe Supervision

• Active and Latent Conditions
• Poor CRM
• Loss of situational awareness

Preconditions for Unsafe Acts
Unsafe Acts

• Active Conditions
• Failed to scan instruments
• Penetrated IMC when VFR only

Failed or Absent Defenses
Adapted from Reason (1990)
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Breakdown of a Productive System

• Latent Conditions
• Excessive cost cutting
• Inadequate promotion policies

• Latent Conditions
• Deficient training program
• Improper crew pairing

Unsafe Supervision

• Active and Latent Conditions
• Poor CRM
• Loss of situational awareness

Preconditions for Unsafe Acts
Unsafe Acts

• Active Conditions
• Failed to scan instruments
• Penetrated IMC when VFR only

Failed or Absent Defenses

• Accident Injury
• Crashed into side of
• mountain

Adapted from Reason (1990)
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The Human Factors Analysis and Classification
System (HFACS)
Shappell, S. and Wiegmann, D. A human error
approach to accident investigation The Taxonomy
of Unsafe Operations. International Journal of
Aviation Psychology, 7, 269-291, 1998. Shappell,
S. and Wiegmann, D. Human factors analysis of
aviation accident data Developing a needs-based,
data-driven, safety program. Proceedings of the
HESSD, Brussels, Belgium, 1999. Shappell, S. and
Wiegmann, D. The Human Factors Analysis and
Classification System HFACS. Office of
Aviation Medicine Technical Report No.
DOT/FAA/AM-00/7. Civil Aeromedical Institute,
Oklahoma City, OK 73125, 2000. Shappell, S. and
Wiegmann, D. Beyond Reason Defining the holes
in the Swiss Cheese. Human Factors in Aviation
Safety, (in press), 2000.
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UNSAFE ACTS
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UNSAFE ACTS
Errors
Violations
Perceptual Errors
Skill-Based Errors
Exceptional
Routine

• Rule-based Decisions
• - If X, then do Y
• - Highly Procedural
• Choice Decisions
• - Knowledge-based
• Ill-Structured Decisions
• - Problem solving

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UNSAFE ACTS
UNSAFE ACTS
Errors
Violations
Perceptual Errors
Exceptional
Routine

• Attention Failures
• - Breakdown in visual scan
• - Inadvertent operation of control
• Memory Failure
• - Omitted item in checklist
• - Omitted step in procedure
• Stick-and-Rudder Skills

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UNSAFE ACTS
UNSAFE ACTS
Errors
Violations
Perceptual Errors
Exceptional
Routine

• Misjudge Distance,
• Altitude, Airspeed
• Spatial Disorientation
• Visual Illusions

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UNSAFE ACTS
Errors
Perceptual Errors
Exceptional

• VFR Flight into IMC
• Elected to File VFR in Marginal Weather
  Conditions
• Failed to Use Radar Advisories from ATC
• Inadequate Brief and Limits on Mission
• IFR Procedure Not Followed
• Weight and Balance Exceeded
• Procedure/Directives Not Followed
• Operating With Known Deficiencies
• Min. Descent Altitude not Complied with

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UNSAFE ACTS
Errors
Perceptual Errors
Routine
Exceptional

• Violated NATOPS/Regulations/SOP
• - Performed Unauthorized Acrobatic Maneuver
• - Canyon Running
• - Failed to Complete Performance Computations
  for Flight
• - Failed to Obtain Valid Weather Brief
• Accepted Unnecessary Hazard
• Not Current/Qualified for Mission
• Exceeded Limits of Aircraft

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PRECONDITIONS FOR UNSAFE ACTS
PRECONDITIONS FOR UNSAFE ACTS
Substandard Conditions of Operators
Substandard Practices of Operators
Adverse Physiological States
Physical/ Mental Limitations
Adverse Mental States
Personal Readiness
Crew Resource Mismanagement

• Loss of Situational Awareness
• Circadian dysrhythmia
• Alertness (Drowsiness)
• Overconfidence
• Complacency
• Task Fixation

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• Spatial Disorientation
• Visual Illusions
• G-induced Loss of Consciousness
• Hypoxia
• Medical Illness

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• Lack of Sensory Input
• Limited Reaction Time
• Incompatible Physical Capabilities
• Incompatible Intelligence/Aptitude

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Crew Resource Mismanagement

• Not Working as a Team
• Poor Aircrew Coordination
• Improper Briefing Before a Mission
• Inadequate Coordination of Flight

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• Readiness Violations
• Crew Rest Requirements
• Bottle-to-Brief Rules
• Self-Medicating
• Poor Judgement
• Poor Dietary Practices
• Overexertion While Off Duty

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UNSAFE SUPERVISION
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Planned Inappropriate Operations
Failed to Correct Problem
Inadequate Supervision
Supervisory Violations

• Failure to Administer Proper Training
• Lack of Professional Guidance

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UNSAFE SUPERVISION
UNSAFE SUPERVISION
Planned Inappropriate Operations
Failed to Correct Problem
Inadequate Supervision
Supervisory Violations

• Mission Risk without Benefit
• Improper Work Tempo
• Poor Crew Pairing

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UNSAFE SUPERVISION
UNSAFE SUPERVISION
Planned Inappropriate Operations
Failed to Correct Problem
Inadequate Supervision
Supervisory Violations

• Failure to Correct Inappropriate Behavior
• Failure to Correct a Safety Hazard

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UNSAFE SUPERVISION
UNSAFE SUPERVISION
Planned Inappropriate Operations
Failed to Correct Problem
Inadequate Supervision

• Not Adhering to Rules and Regulations
• Willful Disregard for Authority by
• Supervisors

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• Human
• Monetary
• Equipment/Facility

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• Structure
• Policies
• Culture

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• Operations
• Procedures
• Oversight

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ORGANIZATIONAL INFLUENCES
Organizational Climate
Resource Management
Organizational Process
UNSAFE SUPERVISION
Planned Inappropriate Operations
Failed to Correct Problem
Inadequate Supervision
Supervisory Violations
PRECONDITIONS FOR UNSAFE ACTS
PRECONDITIONS FOR UNSAFE ACTS
Substandard Conditions of Operators
Substandard Conditions of Operators
Substandard Practices of Operators
Adverse Physiological States
Physical/ Mental Limitations
Crew Resource Mismanagement
Adverse Mental States
Adverse Mental States
Personal Readiness
UNSAFE ACTS
Errors
Errors
Violations
Perceptual Errors
Skill-Based Errors
Decision Errors
Routine
Exceptional
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U.S. NAVY/MARINE CORPS
AVIATION ACCIDENT DATA
Wiegmann, D. and Shappell, S. Human error and
crew resource management failures in Naval
Aviation mishaps A review of U.S. Naval Safety
Center Data, 1990-96. Aviation, Space and
Environmental Medicine, 70, 1147-1151,
1999. Wiegmann, D. and Shappell, S. U.S. Navy
and Marine Corps Tactical Air and Rotary Wing
Class A mishaps 1990 1996 A comprehensive
analysis of crew resource management errors.
Proceedings of the Tenth Symposium for Aviation
Psychology, Ohio State University,
1997. Shappell, S. and Wiegmann, D. Is
proficiency eroding among U.S. Naval aircrews? A
quantitative analysis using the Human Factors
Analysis and Classification System. Proceedings
of the 44th Annual Meeting of the Human Factors
and Ergonomics Society, San Diego, California,
2000.
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Sample of the Types of Human Error Typically Found
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USN/USMC Methodology

• Analyzed all Class A Mishaps between FY91-99
  associated with human error (n178)
• Analyses included all human causal factors as
  identified in the original investigation and
  endorsed by the Chain of Command
• NO new causal factors were identified
• Raters
• 2 Aerospace Psychologists
• 2 Flight Surgeons
• Airframe Rated Pilot/NFO Subject Matter Experts

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Percentage of Human Error Mishaps Associated with
Violations (FY 91-97)

• -.487, ns

Percentage
Fiscal Year
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Intervention Strategy

• Professionalism
• Accountability
• Enforcing the Rules

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Percentage of Human Error Mishaps Associated with
Violations (FY 91-99)
Percentage
Fiscal Year
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U.S. AIR CARRIER
AVIATION ACCIDENT DATA
Shappell, S. and Wiegmann, D. Unraveling the
mystery of general aviation controlled flight
into terrain accidents using HFACS. Proceedings
of the Eleventh Symposium for Aviation
Psychology, Ohio State University,
2001. Wiegmann, D. and Shappell, S. Human error
analysis of commercial aviation accidents
Application of the Human Factors Analysis and
Classification System (HFACS). Proceedings of the
Eleventh Symposium for Aviation Psychology, Ohio
State University, 2001. Wiegmann, D. and
Shappell, S. Human error analysis of commercial
aviation accidents Application of the Human
Factors Analysis and Classification System
(HFACS). Aviation, Space and Environmental
Medicine, (in press), 2001.
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U.S. Air Carrier Methodology

• Analyzed all FAR Part 121 and 135 Air Carrier
  Accidents occurring between FY90-99 associated
  with human error (n785)
• Analyses included all human causal factors as
  identified by the NTSB
• NO new causal factors were identified

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FAR Part 121 135 Scheduled Carriers
Skill-based Errors
Percentage of Accidents
Decision Errors
Violations
Perceptual Errors
Year
Percentages do not add up to 100
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FAR Part 121 135 Scheduled Carriers Alaska
vs. Rest of US
Alaska
Rest of US
Percentage of Accidents
Skill-based Errors
Perceptual Errors
Decision Errors
Violations
Percentages do not add up to 100
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U.S. GENERAL AVIATION
AVIATION ACCIDENT DATA
Shappell, S. and Wiegmann, D. Unraveling the
mystery of general aviation controlled flight
into terrain accidents using HFACS. Proceedings
of the Eleventh Symposium for Aviation
Psychology, Ohio State University, 2001.
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U.S. General Aviation Methodology

• The 15,744 accidents were associated with over
  35,000 human causal factors as reported by the
  National Transportation Safety Board (NTSB).
• These causal factors were classified into HFACS
  causal categories independently by five GA
  pilots.
• - All were certified flight instructors
• - Mean flight hours 3,530

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FAR Part 91 - General Aviation Fatal
Aircrew-Related Accidents
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FAR Part 91 - General Aviation Non-Fatal
Aircrew-Related Accidents
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FAR Part 91 - General Aviation Fatal vs.
Non-Fatal Accident Comparison
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FAR Part 91 - General Aviation Alaska vs. Rest
of US
Alaska
Rest of US
Percentage of Accidents
Skill-based Errors
Perceptual Errors
Decision Errors
Violations
Percentages do not add up to 100
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FAR Part 91 - General Aviation CFIT vs. Non-CFIT
CFIT
Non-CFIT
Percentage of Accidents
Skill-based Errors
Perceptual Errors
Decision Errors
Violations
Percentages do not add up to 100
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HFACS Transition to Military and Civilian
Organizations
Military Organizations Status U.S.
Navy/Marine Corps Implemented U.S.
Army Implemented U.S. Air
Force Limited Implementation U.S. Coast
Guard Limited Implementation Israeli Air
Force Limited Implementation Canadian
Defense Forces Implemented Civilian
Organizations Status Southwest
Airlines Implementation Underway
NASA-Langley Implemented
FAA Implemented NTSB Under
Consideration Federal Railway
Administration Under Consideration
Eurocontrol Modified Implementation Other
Civilian and Military Organizations Human
Factors Society - 7 workshops Aerospace Medical
Association - 3 workshops International
Symposium of Aviation Psychology - 4 workshops
Canadian Aviation Safety Seminar - 2 workshops
Australian Aviation Psychology Symposium - 1
workshop Society of Automotive Engineers -
1 workshop Over 50 invited addresses and
presentations