Human Factors in Aviation Maintenance

• Introduction to Human Factors in Aviation Maintenance

The Need to Consider Human Factors

• Early aviation focused on aircraft design and pilot skills.
• As technology advanced, the role of people became more important.
• Human factors emerged to support pilots with stabilization and automation.
• Understanding human factors is crucial for aircraft maintenance engineers.
• Human factors impact every aspect of their job.

What are Human Factors?

• "Human factors" is used differently across aviation.
• It includes cockpit design and Crew Resource Management (CRM).
• Broadly, it concerns any consideration of human involvement in aviation.
• In maintenance, it's a relatively new focus, highlighted by accidents like Aloha (1988) and the BAC 1-11 windscreen incident (1990).
• These accidents aren't the first events caused by human error, but the events brought human factors into focus.

Definition of Human Factors

• Human Factors: the study of human capabilities and limitations in the workplace.
• It examines the interaction of maintenance personnel, the equipment they use, procedures, and environmental conditions.
• The aim is to optimize the relationship between maintenance personnel and systems to improve safety, efficiency, and well-being.
• Attributes include human physiology and psychology.
• Psychology includes perception, cognition, memory, social interaction, and error.
• Also encompasses workplace design, environmental conditions, human-machine interface, and anthropometrics.
• Anthropometrics is the study of measurements of the human body.

The SHEL Model

• The SHEL model is used to understand human factors and structure related issues.
• SHEL is derived from the initial letters of its components: Software, Hardware, Environment, and Liveware.
• Software includes maintenance procedures and manuals.
• Hardware includes tools, test equipment, and aircraft physical structure.
• Environment includes physical conditions like hangar environment and work environment like work patterns.
• Liveware represents the human element, including maintenance engineers, supervisors, planners, and managers.

The SHEL Model Interfaces

• Human factors focuses on the interfaces between the human element and other SHEL components.
• Safety can be compromised if these interfaces are deficient.
• Software deficiencies include misinterpretation of procedures and poorly designed manuals.
• Hardware deficiencies include insufficient tools and poor aircraft design for maintainability.
• Environmental deficiencies include uncomfortable workplaces and poor lighting.
• Liveware deficiencies include poor relationships with other people and lack of supervision.
• Man, the "Liveware", can perform many activities though modern aircraft use updated computing power.
• To ensure safety, other aspects of the SHEL model must be designed to assist human performance and respect limitations.

Addressing Human Unreliability

• Humans are intrinsically unreliable, but this can be mitigated through training, procedures, tools, and inspections.
• Aircraft design can be improved to reduce the potential for error.

Human Error Statistics

• In 1940, approximately 70% of aircraft accidents were attributable to human error.
• A review by IATA 35 years later found no reduction in this component.
• A 1986 study in the USA identified causes in 93 aircraft accidents.
• Pilot deviation from procedures was a factor in 33% of accidents.
• Inadequate cross-check by the second crew member was a factor in 26% of accidents.
• Maintenance and inspection deficiencies were a factor in 12% of accidents.

Maintenance-Related Accident Factors

• Maintenance and inspection deficiencies are major contributors to accidents.
• The UK CAA found "maintenance or repair oversight / error / inadequate" to be a top 10 causal factor in fatal accidents (1980-1996).
• Human factors problems in aircraft maintenance engineering are a significant issue.

Examples of Incidents and Accidents

• Several high-profile incidents and accidents have involved maintenance human factors problems:
• Accident to Boeing 737, (Aloha flight 243), Maui, Hawaii, April 28 1988
• Accident to BAC One-Eleven, G-BJRT (British Airways flight 5390), over Didcot, Oxfordshire on 10 June 1990
• Incident involving Airbus A320, G-KMAM at London Gatwick Airport, on 26 August 1993
• Incident involving Boeing 737, G-OBMM near Daventry, on 23 February 1995.
• The Aloha flight 243 accident involved a sudden structural failure.
• Post-accident analysis revealed over 240 cracks in the aircraft's skin.
• The US initiated a research program focusing on human factors in aircraft maintenance as a result.
• Contributing factors to accidents:
  • Captain ignored crew inputs
  • Air traffic control failures or errors
  • Improper crew response during abnormal conditions
  • Insufficient or incorrect weather information
  • Runways hazards
  • Air traffic control/crew communication deficiencies
  • Improper decision to land

Incident Examples

• BAC1-11 Windscreen Incident (1990):
  • A windscreen blew out due to the use of incorrect bolts.
  • A shift maintenance manager (SMM) replaced the windscreen himself to save time.
  • The SMM used 7D bolts in place of 8D bolts, because of a shortage.
  • The SMM failed to notice discrepancies.
  • Contributing human factors included perceptual errors, poor lighting, failure to wear spectacles, circadian effects, and organizational factors.
• Airbus 320 Incident (1993):
  • An aircraft exhibited an roll after a flap change.
  • Spoilers were placed in maintenance mode without collars and flags.
  • The engineers misunderstood the spoiler function and didn't brief on the status during shift handover.
• Boeing 737-400 Incident (1995):
  • An aircraft suffered a loss of oil pressure.
  • HP rotor drive covers were not refitted after borescope inspections.
  • The base maintenance controller and fitter failed to refit the covers and no engine runs were carried out.
  • All three UK incidents involved qualified engineers and were characterized by:
    • Staff shortages
    • Time pressures
    • Night work

Preventing Incidents

• Incidents were avoidable if things had been done differently.
• Individuals failed to recognize or react to potential hazards and were open to committing an error.
• Many incidents involve a series of human factors problems that form an error chain.
• If one link in the chain is broken, incidents may have been prevented.

Murphy's Law and Complacency

• Complacency, the belief that accidents won't happen to "me" or "my Company," is a problem.
• Organizations should address human factors issues and implement improvements.
• "Murphy's Law" suggests that if something can go wrong, it will.
• Persuading people to acknowledge Murphy's Law can help overcome complacency.
• Errors can occur even in "safe" organizations and be made by experienced individuals.

Factors in Accidents

• Shift or task handovers were involved.
• Supervisors were doing hands-on tasks.
• There was a "can-do" attitude.
• Interruptions occurred.
• There was a failure to use approved data or company procedures.
• Manuals were confusing.
• There was inadequate pre-planning, equipment, or spares.