Chapter 1 Why We Have to do Maintenance

Why Maintenance Provides assurance Flight Safety Reliability Airworthiness

Engineer’s Role Designer –Design best possible product –May be limited by Money Ability Technique –Man-made entropy Final design may not be optimum Reduced tolerances, cheaper materials Requires additional maintenance

Mechanic Role Technician Repairer Maintainer Goal: Combat natural entropy in systems/components –Deterioration –Misuse –Remove/replace parts –Troubleshoot –Restore systems to intended use

Maintenance Two types –Preventive maintenance (scheduled) Prevent deterioration of system to unusable level Corrective actions Reduce entropy to original level Regular intervals –Various intervals Daily Number of flights Flight hours Cycles

Maintenance Two types –Unscheduled maintenance System breaks rapidly System breaks completely –Definitive, extensive troubleshooting

Maintenance Reliability Level of perfection –Inherent reliability –Maintenance cannot increase level of reliability above this reliability

Redesign Level of perfection increase –Material change New materials New techniques New components –Man-made change Tighter tolerances Improved design skills Design philosophy Natural entropy is reduced –Maintenance schedule will adjust –May increase or decrease schedule

Failure Rate Different patterns of failure –Curve A Early failures –Poor design –Improper parts –Incorrect usage Failure rate levels off –Physical limit/wears out

Failure Rate Different patterns of failure –Curve B Slightly rising rate Definite wear-out period at end –Physical limit/wears out

Failure Rate Different patterns of failure –Curve C Slightly rising rate –No infant mortality or wear-out period –Becomes unusable

Failure Rate Different patterns of failure –Curve D Slow failure rate when new Rises quickly after break-in period Steady level through rest of life

Failure Rate Different patterns of failure –Curve E Steady or slightly rising failure rate No infant mortality or wear-out period

Failure Rate Different patterns of failure –Curve F Infant mortality Level No wear-out period

Maintenance Systemic approach –Reduce peak periods of unscheduled maintenance Management techniques –Equipment techniques –Line replaceable units –Minimum aircraft dispatch requirements

Redundancy Higher desired reliability –Primaries and backups –Primary fails – backup takes over function Radios –Various maintenance techniques possible

Line Replaceable Unit (LPU) Quick replacement –No undue maintenance delays –Failed part Discarded Repaired –No further delay to flight

Minimum Equipment List (MEL) Loss of functionality –Does not effect safety or operation of flight –Manufacturer determined –Regulatory sanctioned –Deferral of maintenance without upsetting mission requirements Maintenance performed within specific time guidelines

Dispatch Deviation Guide(DDG) Instructions for line maintenance Capping connectors from removed units Circuit breakers Prevent inadvertent power-up of specific equipment

Configuration Deviation Guide(CDG) Certain panels missing Configuration differences not affecting safety