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Human Error in Maintenance

Presented by:

Alabama & Northwest Florida Flight Standards District Office


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.


Defining Human Error

Example: John drives into standing water and begins to hydroplane.

1. 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



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.



3. 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.


Error and Aviation Maintenance

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


Valuejet flight 597


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.


Machine/Human Causes for Accidents.

• Human error defined by red line.

• Machine error defined by yellow line.

0

20

40

60

80

100

120

1850 1900 1950 2000 2050


Human Error Estimates*.

System % Due to Human Error

Airlines 70-80%

Air Traffic Control 90%

Ships 80%

Process Control 80%

Nuclear Power 70%

Road Transportation 85%


Table of Aviation Accident Causal Factors.

Causal Factors (1982-1991)

No. of Accidents

Onboard Fatalities

Controlled Flight into Terrain (CFIT)

36 2169

Maintenance and Inspection

47 1481

Loss of Control/Uncontrolled

9 1387

Air Traffic Control 39 1000

Approach and Landing (NO CFIT)

133 910

In-flight smoke and fire

6 610


Table of Aviation Accident Causal Factors.

Ground Deicing/Anti-icing 9 384

Wind shear 10 381

Un-contained Engine Fire 11 199

Out of Configuration Take-off

11 188

Airport Ground Ops. Control

23 138

Rejected Take-off 19 53

TOTAL 394 9639


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--


Heinrich Ratio

Heinrich Ratio

Fatal Accident 1

Non-Fatal Accident 10

Reportable Incident 30

Unsafe Acts 600


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.



• 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.


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.



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


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


A Hangar example


Example: Resulting Damage

• Left-hand horizontal stabilizer.

• Rudder.

• Rear dock stands.

• Hangar wall.


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.


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!


Top Seven Causes of In-Flight Shutdowns

1. Incomplete installation (33%).

2. Damage on installation (14.5%).

3. Improper installation (11%).

4. Equipment not installed or missing (11%).

5. Foreign object damage (6.5%).

6. Improper troubleshooting, inspection, test (6%).

7. Equipment not activated or deactivated (4%).


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.


Top Seven Common Maintenance Errors

1. Incorrect installation of components.2. The fitting of wrong parts.3. Electrical wiring discrepancies (including cross-

connection).4. Loose objects (tools, etc.) left in aircraft.5. Inadequate lubrication.6. Cowlings, access panels and fairings not

secured.7. Landing gear and refuel panels not secured.


Why Do We Make Errors?

?


Mental Limits: Disassembly


Mental Limits: Reassembly


Definition of Culture

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


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?


Culture


List of Organizational and Local Factors.

Organizational Local

Training and selection of personnel.

Knowledge and skill of personnel.

Quality of resources as distributed.

Quality of resources on hangar floor.

Organizational Structure Hangar environment.

Opportunities for career development.

Morale & personalities of employee.


A Human Factors Accident Scenario.

Defenses

Gaps

Teamwork

Reliable Maintenance

Good Management

Ambiguous instruction(goes unchallenged)

Young F/O lets it go

Mis-judgment by senr. Capt.

Missing component

Operational pressureHigh work load.


Error Prevention

Three Basic Strategies


Types of Prevention Design

1. Exclusion Design – The design of a component makes it impossible to commit an error.

2. Prevention Design – The design of a component makes it difficult, but not impossible for error.

3. Fail-Safe Design – The design of a component reduces the consequences of errors without necessarily reducing the likelihood of errors.


Examples of Prevention Design

1. Exclusion design

2. Prevention design

3. Fail-Safe design


Conclusion

Flying is not inherently dangerous, but to an even greater extent than the

sea, it is terribly unforgiving of carelessness, incapacity, or neglect

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