Chapter 1 Why We Have to do Maintenance

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

Guides • Dispatch Deviation Guide (DDG) – Instructions for line maintenance • Capping connectors from removed units • Circuit breakers • Prevent inadvertent power-up of specific equipment • Configuration Deviation List (CDL) – Configuration differences not affecting safety – Certain panels missing

Guides • Non-essential Equipment & Furnishing (NEF) – Do not affect airworthiness – Part of MEL system

Maintenance Program • Scheduled Maintenance/Servicing – Ensure designed level of perfection (Reliability) – Components/systems fail in different ways/rates – Leads to unscheduled maintenance • Overall goal – Smooth workload and manpower requirements

Maintenance Program • Inspections/Modifications dictated by – Aviation regulators – Manufacturers – Airline • Airline maintenance – Programs vary according to operator and activities