USAIR

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A HUMAN FACTORS APPROACH TO ACCIDENT ANALYSIS AND
PREVENTION
Scott Shappell, Ph.D. Civil Aeromedical Institute
Douglas Wiegmann, Ph.D. University of Illinois
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OVERVIEW

• PART 1 Human Factors Approach to Accident
  Investigation and Prevention
• Review Old Concepts
• Introduce New Concepts
• PART 2 Identifying the Problem Areas
• What are the human factors problems?
• What are their causes?
• PART 3 Intervention and Prevention Strategies

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The NTSB estimates that a passenger boarding a
U.S. Carrier today has over a 99.99 chance of
surviving the flight.
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NAVAL AVIATION MISHAP RATE
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COST OF ACCIDENTS
U.S. Navy and Marine Corps FY96-00
Aviation 3.3B
Source U.S. Naval Safety Center

• Shappell Wiegmann, 2000

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REASONS FOR CONCERN

• The rate of improvement has slowed significantly
  and substantially during the last 10 years.
• This has led some to conclude that further
  reductions in accident rates are improbable, if
  not impossible.
• Still, worldwide air traffic is expected to
  double during the next 10 to 15 years.
• Therefore, even if the current level of safety is
  maintained, the number of accidents will
  increase due to the increasing number of aircraft
  and hours flown.

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Projected Traffic Growth and Accident Rates
Adapted from Flight Safety Foundation (1997)
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WHAT MUST WE DO?

• Even greater efforts must be taken to further
  reduce the accident rate.
• In order to achieve this goal, accident
  prevention measures must address the primary
  cause of accidents, which in most cases, is the
  human (ICAO, 1993).

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Human beings by their very nature make mistakes
therefore, it is unreasonable to expect
error-free human performance. Shappell
Wiegmann, 1997

• It is not surprising then, that human error has
  been implicated in 60-80 of accidents in
  aviation and other complex systems.
• In fact, while accidents solely attributable to
  environmental and mechanical factors have been
  greatly reduced over the last several years,
  those attributable to human error continue to
  plague organizations.

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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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Wiegmann, D. Shappell, S. (In review). Human
error analysis of commercial aviation accidents
Application of the Human Factors Analysis and
Classification System (HFACS). Aviation, Space,
and Environmental Medicine.
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Wiegmann, D. Shappell, S. (In review). Human
error analysis of commercial aviation accidents
Application of the Human Factors Analysis and
Classification System (HFACS). Aviation, Space,
and Environmental Medicine.
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ADDRESSING THE PROBLEM

• What was required, therefore, was a general human
  error framework around which accident
  investigation and prevention programs can be
  developed.
• We explored several off-the-shelf approaches

• SHEL Model (Edwards, 1972)
• Traditional Information Processing Approach
  (Wickens and Flach, 1988)
• Failure Analysis Model (Rasmussen, 1982)
• Domino Theory (Heinrich, et al., 1931 Bird,
  1974 Adams, 1976)
• Swiss Cheese Model of Human Error (Reason, 1990)

Shappell, S. and Wiegmann, D. Controlled flight
into terrain The utility of an information
processing approach to mishap causal factors.
Proceedings of the Eighth Symposium for Aviation
Psychology, Ohio State University, 1300-1306,
1995. Wiegmann, D and Shappell, S. Human factors
in U.S. Naval aviation mishaps An information
processing approach. Proceedings of the Eighth
Symposium for Aviation Psychology, Ohio State
University, 1995. Wiegmann, D. and Shappell, S.
Human factors analyses of post-accident data
Applying theoretical taxonomies of human error.
International Journal of Aviation Psychology, 7,
67-81, 1997.
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Human Factors Whats in a Name?

• Human factors means different things to
  different people.

• Pilot Error
• Ergonomics
• Aeromedical Issues
• CRM
• Organizational Factors

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A comprehensive Human Factors Analysis and
Classification System (HFACS) has recently been
developed to help put all these pieces together.
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HFACS Guiding Principles
Principle 1 Aviation is similar in nature to
other complex productive systems. Principle 2
Human errors are inevitable within such a
system. Principle 3 Blaming an error on the
pilot is like blaming a mechanical failure on
the aircraft. Principle 4 An accident, no matter
how minor, is a failure of the system. Principle
5 Accident investigation and error prevention
go hand-in-hand.
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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 VMC only

Failed or Absent Defenses

• Accident Injury
• Crashed into side of
• mountain

Adapted from Reason (1990)
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Where do we usually look to prevent accidents?
Organizational Factors
Unsafe Supervision
Preconditions
Unsafe Acts
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Where should we look to prevent accidents?
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SUMMARY

• HFACS provides
• A framework for understanding the big picture.

• Highlights important human factors safety issues
  and their interrelationships.
• What are the holes in the cheese?
• Arent they too numerous to define?
• Helps target the need for specific intervention
  strategies.
• How can HFACS be used to prevent accidents
  before they occur?

?
?
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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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Breakdown of a Productive System
Latent Conditions
Latent Conditions
Unsafe Supervision
Active and Latent Conditions
Preconditions for Unsafe Acts
Unsafe Acts
Active Conditions
Failed or Absent Defenses
Accident Injury
Adapted from Reason (1990)
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ACCIDENT ANALYSIS OVERVIEW

• Narrative Summary
• Overview of the Accident
• Human Causal Factors
• Accident Analysis Summary Table

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NARRATIVE SUMMARY
On April 22, 1992 at 1553 local time, a Beech
Model E18S (BE 18) registered to Scenic Air Tours
(SAT) collided with Mount Haleakala on the island
of Maui, HI (National Transportation Safety
Board, 1993). Tragically, the pilot and eight
passengers sustained fatal injuries as the
airplane was destroyed by impact forces and a
post-crash fire.
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HFACS ANALYSIS

• The pilot deviated from the planned flight
• A radar track of SAT Flight 22 put the aircraft
  north, rather than south, of the planned flight
  until roughly 2 min before impact with Mt.
  Haleakala.

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HFACS ANALYSIS

• The pilot deviated from the planned flight
• Why then did the captain make such a critical
  navigation error?
• Decision error - the pilot consciously chose the
  310 radial.
• OR
• Skill-based error - the pilot forgot to switch
  the OBS when switching his navigation aids to the
  desired course.

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HFACS ANALYSIS

• The pilots decision to continue the flight into
  instrument meteorological conditions (IMC)
• Violation
• Failure to recognize (misdiagnosed) the
  significance of a cloud layer produced by
  orographic phenomenon.
• Decision Error
• The pilot failed to see the distinctive cloud
  formation
• Substandard Condition - Adverse Mental State
  (Distraction)
• The pilot failed to rely on instruments when
  encountering IMC
• Skill-based error

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HFACS ANALYSIS

• The pilot significantly misrepresented his
  experience
• Substandard Practice Readiness Violation
• Lack of a preemployment background check by SAT
• Resource Management/Organizational Policy
• The FAA failed to require commercial operators to
  conduct substantive pilot preemployment screens
• Outside Influence

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HFACS Scenic Air Tours Flight 22

• Latent Conditions
• Failed to conduct background check

Latent Conditions
Unsafe Supervision

• Active and Latent Conditions
• Physical/mental limitation
• Misrepresented Credentials

Preconditions for Unsafe Acts
Unsafe Acts

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

Failed or Absent Defenses

• Accident Injury
• Crashed into side of
• mountain

Adapted from Reason (1990)
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Air Florida Boeing 737-222 N62AF January 13, 1982
A small, congested midcity airport, freezing
conditions in a snowstorm, dense traffic
movements, and delays occasioned by temporary
closure of the runway, all contributed to the
buildup of psychological pressures that were to
fatally tax the judgment of a young and
relatively inexperienced airline crew (Job,
1996).
Job, 1996
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Job, 1996
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HFACS ANALYSIS

• The Captain did not respond correctly to
  stickshaker activation.
• Unsafe Act, Error, Decision Error
• Pressure to NOT use excessive thrust.
• Organizational Influence, Operational Process
• Although the F/O expressed concern that something
  was not right to the Captain four times during
  the takeoff, the Captain took no corrective
  action to reject the takeoff.
• Precondition, Substandard Practice, Crew
  Resource Mismanagement

Job, 1996
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HFACS ANALYSIS

• Perceived pressure to get under way after a long
  delay and incoming traffic.
• Adverse Mental State
• The flightcrew attempted to deice the aircraft by
  positioning the aircraft near the exhaust of the
  aircraft ahead in line.
• Violation

Job, 1996
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HFACS ANALYSIS

• The flightcrew did not use engine anti-ice during
  ground operation or takeoff.
• Decision Error or Violation
• Contrary to Air Florida procedures, neither
  engine inlet plugs nor pitot/static covers were
  installed during deicing of Flight 90.
• Skill-based or Violation
• The aircraft was deiced by American Airlines
  personnel using procedures that were not
  consistent with American Airlines own procedures.
• Violation

• Neither the maintenance representative nor the
  Captain verified that the aircraft was free of
  snow or ice contamination before pushback and
  taxi.
• Violation

Job, 1996
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HFACS ANALYSIS

• Lack of experience of Captain prior to upgrade.
• Resource Management
• Limited experience of the flightcrew in jet
  transport winter operations.
• Inadequate Supervision
• or
• Operational Process

Job, 1996
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HFACS Air Florida

• Latent Conditions
• Inadequate promotion policies

• Latent Conditions
• Inadequate training

Unsafe Supervision

• Active and Latent Conditions
• Poor CRM

Preconditions for Unsafe Acts
Unsafe Acts

• Active Conditions
• Violated de-ice procedures
• Failed to use adequate thrust

Failed or Absent Defenses

• Accident Injury
• Crashed into bridge

Adapted from Reason (1990)
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Intervention Filling the Holes in the Cheese
Organizational Factors
Safe Decisions
Unsafe Supervision
Safe Supervision
Preconditions for Unsafe Acts
Preconditions for Safe Acts
Unsafe Acts
Safe Acts
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A prescription without diagnosis is
malpractice. Socrates
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U.S. NAVY/MARINE CORPS
AVIATION ACCIDENT DATA
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Sample of the Types of Human Error Typically Found
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Number and Percentage of Mishaps Associated with
Each HFACS Causal Category (FY 91-99)
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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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Percentage of Human Error Mishaps Associated
with Skill-based Errors (FY 91-99)

• .832, plt.01

Percentage
Fiscal Year
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Preliminary Intervention Strategy

• Improve instrument scan
• Prioritizing attention
• Recognizing extremis situations
• Refine basic flight skills (Stick-and-Rudder)
• Practice procedures
• Review the mishap database!

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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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Percentage of Human Error Mishaps Associated
with Crew Resource Management Failures (FY 91-98)

• .551, ns

Percentage
Fiscal Year
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Preliminary Intervention Strategy

• Platform specific training
• Use of video feedback
• Restructure tasks (i.e., EPs)

• Change group composition
• Attempt to change attitudes
• Additional research...

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Percentage of Human Error Mishaps Associated
with Crew Resource Management Failures (FY 91-99)
Percentage
Fiscal Year
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U.S. AIR CARRIER
AVIATION ACCIDENT DATA
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Sample of the Types of Human Error Typically Found
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FAR Part 121 135 Scheduled Carriers
Aircrew-related accidents involving Skill-based
Errors
Percentage of Accidents
Fiscal Year
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FAR Part 121 135 Scheduled Carriers
Aircrew-related accidents involving Decision
Errors
Percentage of Accidents
Fiscal Year
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FAR Part 121 135 Scheduled Carriers
Aircrew-related accidents involving CRM Failures
Percentage of Accidents
Fiscal Year
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FAR Part 121 135 Scheduled Carriers
Aircrew-related accidents involving Violations
Percentage of Accidents
Fiscal Year
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FAR Part 121 135 Scheduled Carriers
Aircrew-related accidents involving
Supervisory/Organizational Factors
Percentage of Accidents
Fiscal Year
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U.S. General Aviation
AVIATION ACCIDENT DATA
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Methodology

• Analyzed all fatal FAR Part 91 - GA accidents
  occurring between 1990 and 1998 associated with
  aircrew error (n2,297).
• A similar analysis of 2,212 randomly selected
  non-fatal GA accidents was conducted.
• The 4,509 accidents were associated with over
  14,000 human causal factors, as reported by the
  National Transportation Safety Board (NTSB).
• The NTSB human causal factors were classified
  into HFACS causal categories independently by
  five GA pilots.
• - All were certified flight instructors
• - Mean flight hours 3,530
• - Inter-rater reliability K.72

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FAR Part 91 - General Aviation Fatal
Aircrew-Related Accidents
N2297
Skill-based Errors
Percentage of Accidents
Violations
Decision Errors
Perceptual Errors
Incomplete
Year
Percentages do not add up to 100
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FAR Part 91 - General Aviation Non-Fatal
Aircrew-Related Accidents
N2212
Percentage of Accidents
Skill-based Errors
Decision Errors
Violations
Perceptual Errors
Incomplete
Year
Percentages do not add up to 100
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FAR Part 91 - General Aviation Fatal vs.
Non-Fatal Accident Comparison
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Factors Affecting the Validity of a Taxonomy
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HFACS can be applied anywhere!
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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 Implemented Israeli Air
Force Limited Implemented Canadian
Forces Implemented Civilian
Organizations Status Southwest
Airlines Implementation Underway Transport
Canada Under Consideration
NASA-Langley Implemented NASA-Ames
ASRS Under Consideration
FAA Implemented Other Civilian and
Military Organizations Human Factors Society -
5 workshops Aerospace Medical Association - 2
workshops Association of Aviation
Psychologists - 2 workshops Canadian
Aviation Safety Seminar - 2 workshops
Australian Aviation Psychology Symposium - 1
workshop Society of Automotive Engineers -
1 workshop Over 30 invited addresses and
presentations
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Whenever we talk about pilots who have been
killed in a flying accident, we should all keep
one thing in mind. They made a judgment. They
believed in it so strongly that they knowingly
bet their lives and those of their passengers on
it. That their judgment was faulty is a tragedy.
Many of us here today had the opportunity to
influence their judgment, so a little bit of all
of us goes with everyone we lose. Anonymous as
modified by Shappell and Wiegmann (2000)