Douglas Wiegmann, Ph.D.Douglas Wiegmann, Ph.D.University of IllinoisUniversity of Illinois

HFACS ANALYSIS OF GENERAL AVIATION HFACS ANALYSIS OF GENERAL AVIATION ACCIDENT DATA: IMPLICATIONS FOR ACCIDENT DATA: IMPLICATIONS FOR AERONAUTICAL DECISION-MAKINGAERONAUTICAL DECISION-MAKING

Scott A. Shappell, Ph.D.Scott A. Shappell, Ph.D.Civil Aeromedical InstituteCivil Aeromedical Institute

FAA-99-G-006FAA-99-G-006

Errors

PerceptualErrors

Skill-BasedErrors

UNSAFEACTS

Errors

DecisionErrors

ExceptionalRoutine

Violations

InadequateSupervision

PlannedInappropriate

Operations

Failed toCorrectProblem

SupervisoryViolations

UNSAFESUPERVISION

Substandard Conditions of

Operators

PRECONDITIONSFOR

UNSAFE ACTS

Substandard Conditions of

Operators

PRECONDITIONSFOR

UNSAFE ACTS

Adverse Physiological States

Physical/Mental

Limitations

Adverse Mental States

Adverse Mental States

Personal Readiness

Crew Resource Mismanagement

Substandard Practices of Operators

ResourceManagement

OrganizationalClimate

OrganizationalProcess

ORGANIZATIONALINFLUENCES

Errors

PerceptualErrors

Skill-BasedErrors

UNSAFEACTS

Errors

DecisionErrors

ExceptionalRoutine

Violations

Substandard Conditions of

Operators

PRECONDITIONSFOR

UNSAFE ACTS

Substandard Conditions of

Operators

PRECONDITIONSFOR

UNSAFE ACTS

Adverse Physiological States

Physical/Mental

Limitations

Adverse Mental States

Adverse Mental States

Personal Readiness

Crew Resource Mismanagement

Substandard Practices of Operators

A comprehensive review of fatal 14 CFR Part 91 accidents between January 1990 and December 1998 was conducted using database records maintained by the NTSB and the FAA.

A total of 2,391 accidents was identified for further analysis

Only those accidents in which the accident investigation was completed and causal factors determined were included in this analysis.

MethodMethod

The 5,893 causal factors associated with these 2,391 accidents were independently coded by five general aviation pilots

This HFACS coding focused solely on the causal factors identified by the NTSB during the original accident investigation.

No new cause factors were created during this error-

coding process.

MethodMethod

Coders:• Five general aviation pilots/certified flight instructors• Flight hours ranged from 1,250 to 11,000

Training:• Four-hour workshop on HFACS• Practice coding 20 accidents as a group• Practice coding 50 accidents independently, followed by a

review/consensus meeting

MethodMethod

Aircraft Control Not MaintainedProcedures/Directives Not Followed

Abort DelayedAirspeed (VREF) Not Maintained

APU SelectedProper Touchdown Point Misjudged

Abort Above V1 ImproperAirspeed (VMC) Not MaintainedAutopilot Improper Use OfComplacencyControl Interference Inadvertent

Crew/Group Coordination Not MaintainedProper Touchdown Point Not AttainedAirspeed Not MaintainedAirspeed (VR) ImproperAutopilot Inadvertent Deactivation

Circuit Breaker SelectedCompensation for Wind Conditions Not PossibleFlare ImproperUnsafe/Hazardous Condition Not IdentifiedVFR Flight Into IMC AttemptedFlight Into Adverse Weather ContinuedHydraulic System Not SelectedInadequate Surveillance of Operation

Proper Touchdown Point Not Possible

Aborted Takeoff DelayedAirspeed (VLOF) Not AttainedAirspeed ExcessiveAltimeter Setting Not ObtainedAltitude Not MaintainedBecame Lost/DisorientedChecklist Not Complied WithCrew/Group Coordination Not PerformedFlaps Improper Use OfFlare ExcessiveFlight into Known Adverse Weather InitialedGo-Around Not PerformedIdentification of Aircraft Visually DelayedInadequate Substantiation Process

Visual Separation Not MaintainedMinimum Descent Altitude Not MaintainedWheels Up Landing InadvertentAircraft Preflight Not Performed

Aircraft Weight and Balance MisjudgedAltimeter Not UsedChecklist Inaccurate

Compensation For Wind Conditions InadequateDescent ExcessiveDistance MisjudgedFlare DelayedGround Loop/Swerve Intentional

Remedial Action DelayedVFR Flight Into IMP InitiatedVisual Lookout Not MaintainedAbort Above V1 PerformedCompensation for Wind Conditions ImproperDirectional Control Not Maintained

Diverted AttentionIce/Frost Removal From Aircraft InadequateIFR Procedure ImproperAircraft Control Not PossibleStall InadvertentInadequate Visual LookoutLack of Familiarity With Aircraft

Lack of Total Experience in Type of AircraftLowering of Flaps PerformedPressureVFR Flight Into IMC InadvertentAborted Takeoff PerformedCommunications Not Understood

Emergency Procedure Not Followed

Inadequate Weather EvaluationNosewheel Steering ExcessiveProcedure InadequateRotation ExcessiveVFR Flight into IMC ContinuedEmergency Procedure Not Performed

Lack of Familiarity with Geographic AreaLevel Off Not AttainedMaintenance, Adjustment Improper

Monitoring InadequatePropeller Feathering Not Performed

Remedial Action Not PossibleVisual/Aural PerceptionPreflight Planning/Preparation InadequateAircraft Handling ImproperCrew/Group Coordination Inadequate

Spoiler Extension Not Performed

Stall/Spin InadvertentAirspeed (VREF) Not AttainedAirspeed (VS) Not MaintainedGo-Around Delayed

Fatigue (Flight and Ground Schedule)

Flight to Alternation Not Performed

Operation with Known Deficiencies in EquipmentSpoiler Extension Inadvertent ActivationSupervision InadequatePlanning/Decision improperRaising of Flaps ImproperIn-Flight Planning/Decision Improper

Overconfidence in Personal Ability

Parking Brake Not SetExpectancyFlight Manuals Improper Use Of

Wrong Taxi Route SelectedGear Extension Not PerformedWeather Evaluation InadequateStall/Mush EncounteredParking Brakes Inadvertent DeactivationIn-Flight Planning/Decision Poor

Proper Glidepath Not Maintained

Altitude InadequateConditions/Steps Insufficiently DefinedEvacuation ImproperPassenger Briefing InadequateSpatial DisorientationThrottle/Power Control Improper Use OfWeather Evaluation InaccurateWrong Runway SelectedIce/Frost Removal From Aircraft Not IdentifiedPlanned Approach PoorRecovery from Bounced Landing ImproperPlanning/Decision InadequateAircraft Preflight InadequateChecklist InadequateDescent InadvertentGenerator Inadvertent Deactivation

Touchdown InadvertentPreflight Planning/Preparation ImproperCompensation for Wind Conditions MisjudgedVisual IllusionUncontrolled DescentProper Descent Rate Not Maintained

Checklist Not UsedAnti-Ice/Deice System Not UsedInadequate MonitoringPowerplant Controls Inadvertent ActivationTraffic Advisory Not Identified

Clearance MisjudgedIFR Procedure Not FollowedInattentiveRemedial Action AttemptedSomeone GoofedImproper Use of Preflight Briefing ServiceDescent PrematureProper Descent Rate Not Attained

Airspeed Not Maintained (generic)

Inadvertent StallVisual Lookout InadequateIce/Frost Removal From Aircraft Nor PerformedInformation InsufficientSelf-Induced PressureTrim Setting ImproperFlight Controls Improper Use OfAltitude/Clearance Not Maintained

Maneuver PerformedPreflight Planning/Preparation Poor

Proper Altitude Not MaintainedFlare InitiatedFlight Advisories Not FollowedAltitude/Clearance InadequateDistance/Altitude MisjudgedInadequate TrainingRotation ImproperUnsuitable Terrain or Takeoff/Landing/Taxi AreaVFR Procedures InadequateProper Alignment Not PossibleRemedial Action ImproperFlare MisjudgedProper Alignment DelayedMissed Approach Not Performed

Proper Alignment Not AttainedLack of Total Experience in Type OperationMinimum Descent Altitude Below

Miscellaneous Equipment InitiatedProper Alignment Not Maintained

Supervision ImproperGear Down and Locked Not VerifiedWind Information MisjudgedAircraft Weight and Balance ExceededAircraft Control-UncontrolledCrew/Group Coordination Not AttainedChecklist Not FollowedClearance Not Maintained

Sample of the Types of Human Error Typically Found

Each pilot was assigned 1/3 of the accidents for a given year.

Independently coded NTSB cause factors (no new ones created)

Randomly paired with a second pilot who coded the same set of accidents.

Pilots met to compare codes and achieve consensus

They were then assigned another 1/3 of the accidents for a particular year and randomly paired with another pilot.

This process continued until all the accidents had been coded.

ProcedureProcedure

Reliability of Coding Process

On average, pilot agreed 79% of the time on how the causal factors should be coded using HFACS.

These percentages varied only slight across the years of data analyzed in this study (range was 77% to 83% agreement).

When overall agreement was corrected for chance using Cohen’s Kappa, the resulting index was .722, which is considered “good” by conventional standards.

ResultsResults

0

10

20

30

40

50

60

70

80

90

100

90 91 92 93 94 95 96 97 98

Skill-basedErrors

PerceptualErrors

DecisionErrors

Violations

Per

cen

tage

of

Acc

iden

ts

Year

* Incomplete

Percentages do not add up to 100%

Percentage of Accidents

Category of Cause-factors (%)

Unsafe Acts (73.5%)

Other (26.5%)

Results:Results:

01020

304050607080

90100

Skill-based Violation Decision Perceptual

Types of Unsafe Acts (%)

Type of Unsafe Act

% o

f C

ause

Fac

tors

N = 2597

N = 912N = 714

N = 109

Results:Results:

0102030405060708090

100

90 91 92 93 94 95 96 97 98

Year

Per

cent

age

of C

ause

Fac

tors

Skill-based Errors

Perceptual Errors

Decision ErrorsViolations

Percentage of Cause Factors

inflight planning decision improper

altitude inadequate

judgment poor

inflight planning decision poor

inflight planning decision inadequate

planning decision improper

refueling not performed

aborted take off not performed

low altitude flight maneuver performed

remedial action delayed

aborted landing delayed

wrong runway selected

all available runway not used

weather evaluation inadequate

go around delayed

preflight briefing service disregarded

altitude improper

aerobatics performed

unsuitable terrain for take off landing selected

preflight briefing service not used

hazardous weather advisory disregarded

procedure directives not followed

vfr into imc inadvertent

lift off premature

aborted take off delayed

preflight briefing service not obtained

weather forecast disregarded

go around not performed

altitude low

inflight planning decision delayed

anti ice de ice system not used

proper altitude not selected

flight to alternate destination not performed

weather evaluation misjudged

weather evaluation improper

weather evaluation poor

missed approach not performed

emergency procedure simulated

vfr into imc attempted

pull up excessive

pull up delayed

planned approach improper

planned approach poor

taxi speed excessive

ostentatious display

fuel supply inadequate

carburetor heat improper use of

flight into adverse weather continued

flight into adverse weather inadvertent

low altitude flight maneuver intentional

flight into adverse weather initiated

emergency procedure delayed

flight advisory disregarded

weather forecast not obtained

maneuver excessive

remedial action inadequate

stall spin initiated

missed approach delayed

gear retraction not performed

low pass performed

planning decision poor

carburetor heat not used

flight to alternate destination delayed

updating of recorded weather info not obtained

pull up performed

go around attempted

emergency procedure not performed

altitude clearance inadequate

improper decision

stall spin performed

maneuver performed

remedial action not performed

refueling improper

ac handling improper

proper altitude not maintained

Variety of Decision Codes (N = 185)Variety of Decision Codes (N = 185)

Decision Error FrequencyPoor In-flight Planning 184 (25.8%)

Wrong Altitude Selection 78 (10.9%)

Over Commitment to Plan 50 (7.0%)

Poor Judgment 50 (7.0%)

Poor Flight Planning 36 (5.0%)

Inaccurate Weather Evaluation 22 (3.1%)

Refueling Not Performed 21 (2.9%)

Inadequate Preflight Briefing 20 (2.8%)

Improper Remedial Action 16 (2.2%)

Wrong Maneuver 15 (2.1%)

Top 10 Decision Errors

ac control exceeded

ac control not maintained

ac unattended engine running intentional

ac weight balance continued

ac weight balance disregarded

ac weight balance exceeded

ac weight balance excessive

ac weight balance improper

act clearance not complied

aerobatics attempted

aerobatics improper

aerobatics initiated

aerobatics intentional

aerobatics performed

air speed exceeded

altitude clearance inadequate

altitude disregarded

altitude inadequate

altitude low

ATC clearance not followed

attitude indicator not available

buzzing intentional

buzzing performed

certification improper for flight

decision height disregarded

decision height not complied with

decision height not maintained

decision height not used

descent height disregarded

design stress limits of ac exceeded

dispatch procedures not followed other govt personnel

external navigation lights not used

flight into adverse weather

flight into adverse weather attempted

flight into adverse weather continued

flight into adverse weather improper

flight into adverse weather inadvertent

flight into adverse weather initiated

flight into adverse weather intentional

flight into adverse weather performed

flight into adverse weather selected

flight manuals disregarded

flight navigation instruments inadequate

fuel supply inadequate

hazardous weather advisory disregarded

ice frost removal from ac improper

ifr procedure improper

ifr procedure not followed

impairment alcohol

impairment drugs

inflight briefing service not used

inflight planning decision improper

information insufficient designated examiner

information insufficient pic

loading of cargo improper

low altitude flight maneuver attempted

low altitude flight maneuver intentional

low altitude flight maneuver performed

low pass intentional

low pass performed

maintenance annual inspection not complied with

maintenance annual inspection not performed

maintenance design changes improper pic

maintenance installation improper

maintenance major alteration improper pic

maintenance major repair improper pic

maintenance service bulletin not complied with

maneuver attempted

minimum descent altitude below

minimum descent altitude disregarded

minimum descent altitude not complied with

minimum descent altitude not maintained

minimum descent altitude not obtained/maintained

Variety of Violation Codes (N = 115)Variety of Violation Codes (N = 115)

Violation FrequencyVFR into IMC 262 (28.7%)

Flight into Adverse Weather 157 (17.2%)

Stress Limits Exceeded 87 (9.5%)

IFR Procedure Not Followed 53 (5.8%)

Weight and Balance Exceeded 49 (5.4%)

Aerobatics Performed 48 (5.3%)

Ostentatious Display/Buzzing 48 (5.3%)

Procedure/Directives Not Followed 46 (5.0%)

Operating With Known Deficiencies 40 (4.4%)

Min. Descent Altitude not Complied with 26 (2.9%)

Top 10 Violations

Causal Factor FrequencyVFR into IMC 262 (16.1%)

Poor In-flight Planning 184 (11.3%)

Flight into Adverse Weather 157 (9.7%)

Stress Limits Exceeded 87 (5.4%)

Wrong Altitude Selection 78 (4.8%)

Top 5 Decision Errors/Violations

Top factors involve weather-related issues

These factors have been explore by the Wx JSAT

FAA is sponsoring research to empirically explore these factors (go beyond “expert opinion”)

When decision errors are addressed separately from violations:

Flight planning and management become the top issues

This may be more inline with the traditional conceptualization of ADM

ConclusionsConclusions