Human Error in Maintenance

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Human Error in Maintenance

• Presented by
• Alabama Northwest Florida Flight Standards
  District Office

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Section Objectives

• After you complete this section you will be able
  to
• Define two different types of human error.
• Explain why people commit errors.
• Explain how human error affects AMT.
• Name the types of error prevention.

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Defining Human Error

• Example John drives into standing water and
  begins to hydroplane.
• Slip Having a good plan, but bad execution.
• Ex John knows he should pump his brakes, but
  misses the brake and steps on the gas instead

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Defining Human Error

• 2. Mistake A bad plan is performed, though not
  on purpose.
• Ex John thinks that speeding up will give
  control over his car. He steps on the gas.

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Defining Human Error

• Violation The wrong procedure is performed
  intentionally.
• Ex John learned in drivers education class that
  he should pump his brakes in this situation.
  However, John heard from his older brother that
  acceleration is best, so he steps on the gas.

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Error and Aviation Maintenance

• This section describes how human error affects
  the aviation community, aviation maintenance and
  more specifically the AMT.

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Valuejet flight 597
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Machine/Human Causes for Accidents.

• Airline safety has improved over the past 40
  years because of
• better aircraft.
• better air traffic control.
• better weather prediction.

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Machine/Human Causes for Accidents.

• Human error defined by red line.
• Machine error defined by yellow line.

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Human Error Estimates.
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Table of Aviation Accident Causal Factors.
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Table of Aviation Accident Causal Factors.
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Introduction to Human Error

• For want of a nail, the shoe was lost, for want
  of a shoe, the horse was lost, for want of a
  horse, the rider was lost, for want of a rider,
  the battle was lost
• --Benjamin Franklin--

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Heinrich Ratio
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Active and Latent Errors

• There are two basic kinds of human errors active
  errors and latent errors.
• Active Error An action that has an immediate
  effect.
• Latent Error An action that has a delayed
  effect
• Reason, J. (1990). Human Error, Cambridge, UK
  Cambridge Press.

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Active and Latent Errors

• Active errors Actions that have immediate
  effect. People are most familiar with active
  errors. An example of an active error would be a
  pilot believing his aircraft to be much higher
  than it really is and failing to adjust his
  altitude accordingly. This error leads to the
  plane crashing into a mountainside, an effect
  that is felt more or less immediately in the
  system.

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Active and Latent Errors.

• Latent errors Actions that have delayed effect.
  Latent errors, on the other hand, are errors
  whose effects are delayed in time and space and
  may not be felt immediately. An example would be
  an AMT neglecting to check a key bolt supporting
  an engine to a wing. This bolt happens to be
  corroded. Over time, the engine support weakens
  and fails altogether. Had the AMT not committed
  the latent error of neglect, the corroded bolt
  would have been replaced and the support would
  not have been compromised.

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Active and Latent Errors

• Because of the time delay between error and
  consequence, latent errors and their causes are
  much more difficult to trace than are active
  errors.

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Human Error in Maintenance

• The average cost of an in-flight engine shutdown
  is 500,000.
• The average cost of a flight cancellation is
  50,000.
• The average cost of a return to gate is 15,000.
• The Airline Transport Association estimates that
  ground damage costs 850 million/year.
• The average ground damage incident costs 70,000.
• One Airline estimates between 75-100
  million/year is wasted on error

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A Hangar example
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Example Resulting Damage

• Left-hand horizontal stabilizer.
• Rudder.
• Rear dock stands.
• Hangar wall.

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Example Cost Factors

• Material
• Regular and overtime labor.
• Repair to dock stands and hangar wall.
• Loss of bay during extra repair duration.
• Delayed or third party maintenance for other
  aircraft.
• Operational complications due to aircraft
  availability.
• Investigation and remediation.
• Estimated total cost 900,000.

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Example Cost Implications

• Annual airline revenue 12,000,000,000.
• Revenue/day 33,000,000.
• Estimated profit margin 5
• Profit per day 1,650,000
• Total repair/associated costs 900,000.
• Summary Error Consumed ½ day of total profit!

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Top Seven Causes of In-Flight Shutdowns

• Incomplete installation (33).
• Damage on installation (14.5).
• Improper installation (11).
• Equipment not installed or missing (11).
• Foreign object damage (6.5).
• Improper troubleshooting, inspection, test (6).
• Equipment not activated or deactivated (4).

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Other Maintenance Related Causes of In-Flight
Shutdowns

• Missing parts.
• Incorrect parts.
• Worn parts.
• Careless installation of O-ring.
• B-nuts not safety wired.
• B-nuts wired backwards.
• Nuts not torqued
• Over torquing.
• Not loosening both ends of connections.
• Replacing tube assembly without breaking
  connections.

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Top Seven Common Maintenance Errors

• Incorrect installation of components.
• The fitting of wrong parts.
• Electrical wiring discrepancies (including
  cross-connection).
• Loose objects (tools, etc.) left in aircraft.
• Inadequate lubrication.
• Cowlings, access panels and fairings not secured.
• Landing gear and refuel panels not secured.

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Why Do We Make Errors?

• ?

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Mental Limits Disassembly

•  

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Mental Limits Reassembly
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Definition of Culture

• Culture A pattern of beliefs and expectations
  shared by an organization and its members.

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Culture

• What would happen if an air carrier made on-time
  departure its number one priority?
• How would that affect safety?
• Do you think management would give you the time
  to service an airplane the right way?
• Do you think you would be pressured?

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Culture
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List of Organizational and Local Factors.
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A Human Factors Accident Scenario.
Defenses
Good Management
Reliable Maintenance
Teamwork
Operational pressure High work load.
Missing component
Mis-judgment by senr. Capt.
Young F/O lets it go
Gaps
Ambiguous instruction (goes unchallenged)
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Error Prevention

• Three Basic Strategies

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Types of Prevention Design

• Exclusion Design The design of a component
  makes it impossible to commit an error.
• Prevention Design The design of a component
  makes it difficult, but not impossible for error.
• Fail-Safe Design The design of a component
  reduces the consequences of errors without
  necessarily reducing the likelihood of errors.

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Examples of Prevention Design

• Exclusion design
• Prevention design
• Fail-Safe design

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Conclusion

• Flying is not inherently dangerous, but to an
  even greater extent than the sea, it is terribly
  unforgiving of carelessness, incapacity, or
  neglect