Aeronautical Maintenance Notes

Brief Review of General Maintenance Concepts

  • Evolution of Maintenance:
    • 1950-1960/70s: Repair when it breaks.
    • 1980/1990s: Scheduled revisions, planning and control systems, large and slow computers, maintenance investments, global management, multi-technique teams, benchmarking, efficiency indices, safety/environment/ecology, subcontracting, outsourcing, integrated maintenance systems, condition monitoring, design for reliability and maintainability, risk analysis, small and fast computers, failure mode and effects analysis, polyvalent work teams, expert systems.
    • 2000s: Fourth generation maintenance.
  • Generations of Maintenance Protagonists and Objectives:
    • 1st Generation: Operator; Objective: Repair the failure.
    • 2nd Generation: Maintenance Specialist; Objective: Increase availability.
    • 3rd Generation: Maintenance Engineer; Objective: Control the equipment.
    • 4th Generation: The Manufacturer; Objective: "Less Maintenance".

History of Scheduled Maintenance in Aviation

  • Early days: Maintenance programs developed by mechanics.
  • 1950s: Airplane manufacturers became the source of maintenance program development.
  • 1960s: Industry formed a Task Force to investigate preventive maintenance capabilities, known as "On-condition Maintenance".
  • 1970s: Development of the Maintenance Steering Group (MSG).
  • Since the 1980s: Most aircraft manufacturers use the MSG-3 approach.

Regulations

  • EASA (European Aviation Safety Agency)
    • National Regulations
    • CS 25.1529: Instructions for Continued Airworthiness
  • FAR 25.1529 (Federal Aviation Regulations)
    • "Instructions for Continued Airworthiness in accordance with Appendix H must be prepared."
    • FAR: Federal Aviation Regulations
  • ICAO (International Civil Aviation Organization)
    • ICAO convention ANNEX 8: "Airworthiness of Aircraft"
    • Manufacturer's responsibility to identify Scheduled Maintenance Tasks that form part of the Instructions for Continued Airworthiness (ICA) of the aircraft.

Maintenance Challenges

  • Market:
    • Traffic, "Business", "hub" network, high investment in airplanes, weekly and annual seasonality.
    • Operation: Demand for greater punctuality, shorter transits, higher average daily utilization.
    • Airplanes fly more on weekends and in the summer.
  • Maintenance:
    • Greater reliability of systems.
    • Less time available for troubleshooting.
    • Less time available for maintenance actions.

Maintenance Definitions

  • NF X 60-010: Set of actions that allow maintaining or restoring a property to a specified state or in conditions to ensure a certain service.
  • BS 3811 A: Combination of actions performed to maintain or restore an asset to an acceptable condition.
  • NP (EN) 13306: Combination of all technical, administrative, and management actions during the life cycle of an asset, intended to maintain or restore it to a state in which it can perform the required function.
  • Moubray (RCM II): Actions required for ensuring that physical assets continue to do what their users want them to do.
  • "Typical Airline": Actions required for restoring or maintaining an item in a serviceable condition, including servicing, repair, modification, overhaul, inspection, and determination of condition.
  • FAA: Inspection, overhaul, repair, preservation, and replacement of parts.
  • Kinnison: Process of ensuring that a system continually performs its intended function at its designed-in level of reliability and safety.
  • Aeronautical Maintenance Definition: Set of actions that ensure, during the life cycle of a given asset, that it performs the required function at the levels of safety and reliability incorporated in its design.
    • Emphasis on reliability: Maintaining function with a certain degree of guaranteed continuity.

Maintenance Classification / Maintenance Methods

  • Classification:
    • Programmed vs. Non-Programmed
    • Corrective vs. Preventive (or Predictive)
    • Conditional vs. Systematic
  • Parameters Originating Maintenance Operations:
    • Failure (Partial, Complete)
    • Equipment Status (Inspection, Control, Visit)
    • Deadline
  • Maintenance Operations:
    • Provisional or Palliative Repair
    • Definitive or Curative Repair
  • Methods:
    • Hard Time: Function of time.
    • On Condition: Function of state.
    • Condition Monitoring: No maintenance program.
    • Proactive vs. Reactive: Function of failure.

Maintenance Classification (cont.)

  • Improvement Maintenance (Modification):
    • Of the Design (drawing, material, technology).
    • Of the Maintenance Program (task, interval, technology).
    • Typically originates reactively (learning from failure) and then becomes proactive (preventing failures).
    • Corrective maintenance can take on a proactive character and be programmed or not, depending on safety and economic factors.
    • Modifications are typically programmed and applied "one time".

Operator/MRO Relationship

  • Integrated MRO within the Operator:
    • Almost self-sufficient or slightly self-sufficient organization.
    • Focus on core business, all MRO services are contracted.
  • Operator with Limited MRO:
    • Reduced organization.
    • Long-term contracts with specialized MROs.
  • Operator without MRO:
    • All MRO services are contracted.
    • Only in-house engineering tasks.
  • Contracting Types:
    • Spot contracting.
    • Long-term contracts only for non-existent capacities.
    • Total contracting of all production activities.
    • Total contracting of all maintenance activities to a single provider.

Maintenance Classification by Type of Flight Material

  • VP Maintenance & Engineering
  • Technical Services
  • Aircraft Maintenance
    • Hangar
    • Line
  • Shop Maintenance
    • Avionics
    • Mechanical
    • Structures
  • Material
    • Purchasing
    • Planning
    • Stores
    • Inventory
    • Receiving
  • Maintenance Program
    • Evaluation
    • Engineering
    • Quality Assurance
    • Quality Control
    • Training
    • Reliability
    • Publications
    • Safety
    • Computer
    • MCC

Aircraft Maintenance - "Line"

  • Line Maintenance includes work on the Aircraft that can normally be performed outdoors (on the Line).
  • In Line Maintenance, the following types of work are usually performed on the Aircraft:
    • Transit Check: T, T1, T2
    • Anomaly Correction
    • Replacement of LRUs (Line Replaceable Units)
    • Troubleshooting (detection and characterization of failures)

Transit Inspections - Example A320

  • Examples of inspection areas and items:
    • Forward Area (Areas 1 to 4):
      • Cockpit and cabin windows, pitot and static inlets, AOA, TAT probes and ice detector, radome, fuselage upper and lower areas.
      • Check for dents, service panels, doors and drains, E&E compartment ventilation system inlet and outlet valves.
      • Check crew oxygen system overpressure green disc.
    • Lower Forward Fuselage (Areas 4 to 6):
      • Doors and service panels, antennas.
    • RH Wing Root (Areas 6 to 7):
      • Landing lights, slats, refuel/defuel coupling and control panel.
    • Engine and Mast #2 (Areas 7 to 8):
      • Cowlings, access and overpressure doors, engine mast drain, engine inlets, fan blades, turbine exhaust, ventilation inlets and outlets.
      • Inspect engine drain mast for leaks, check oil level, check case drain filter clogging indication pin.
    • Leading Edge and RH Wing Tip (Areas 8 to 10):
      • Slats, surge tank air inlet, fuel ventilation overpressure disc, fuel water drain valve, navigation lights, wing tip, static discharger.
    • RH Wing Inner Lower and Trailing Edge (Areas 10 to 11):
      • Ailerons, spoilers, flaps.
      • Check pressure of LAF accumulators, wing inner lower area for fuel and hydraulic leaks, drip-sticks inlets, fuel tanks drains, refuel/defuel port.
    • MLG RH/LH Area (Areas 11 to 16):
      • Wheel well, MLG, doors, wheels and tires.
      • Inspect brakes for wear and overheating, check landing gear locking mechanism.
      • Check pressure and scavenge filters clogging pins.
    • Aft Fuselage (Areas 11 to 12 and 15):
      • Antennas, drains, service panels and doors.

Aircraft Maintenance - "Line" (cont.)

  • The degree of technical coverage depends on the Line Maintenance concept adopted in combination with the Pre-flight Check performed by the crew.
  • Each station needs to be analyzed and the concept defined to balance costs with dispatch reliability.
  • Maintenance Concepts:
    • "Call in" Maintenance: Technician available within approximately 1 hour of call.
    • "Stand-by" Maintenance: Technician available within minutes.
    • "Full" Maintenance: Inspections and release performed by technicians always present.
    • "No" Maintenance: No technician available; CCM must organize rescue operation in case of anomalies or AOG.

Aircraft Maintenance - "Base"

  • Base Maintenance includes work on the Aircraft that normally requires docking and must be performed inside appropriate facilities (Hangar) to ensure adequate safety, quality, and airworthiness conditions.
  • In Base Maintenance, the following types of work are usually performed on the Aircraft:
    • VTs: various works, A-Check, B-Check, C-Check, D-Check, Structural Inspection and Repair, Painting, Modifications, Engine Replacement.

Aircraft Maintenance - "Base" (cont.)

  • Specific requirements typically required by Aeronautical Authorities for Base Maintenance (and also Engine and Component Maintenance) to MROs:
    • Adequate facilities, adequate equipment, general tools, special tools, maintenance manuals, trained personnel, work documents, written standards and procedures.

Line and Base Maintenance Example

  • Hangar Layout:
    • Includes areas for Interior of Cabins, Emergency Equipment, Cleaning Workshop, Structures Workshop, Composites Workshop, Removed Material, Useful Material, Rejected Material, Material under Inspection, Machine Workshop, Heat Treatments, Electrolytic Treatments, Painting Workshop, Wheel Workshop, Logistics and Rotables Management, Warehouses, Specialized Repairers, Consignment Warehouses, Pooling, Suppliers, Manufacturers, Customers, and Laboratories.

New Generation Fuel Efficient Engines

  • Trent XWB
    • A350-900: 84Klbs
    • A350-800: 75/79Klbs
    • A350-1000: 93Klbs

Engine Components

  • Fan, Low Pressure Compressor, High Pressure Compressor, Combustion Chamber, High Pressure Turbine, Low Pressure Turbine, Shafts
  • GE, GEnx for A350 - 118” diameter fan selected as optimum performance / noise solution

Engine Facts

  • Engines are among the most complex systems on an aircraft.
  • For a high-bypass turbofan engine:
    • Thrust can exceed 50 tons during takeoff.
    • Centrifugal force on each fan blade can reach 100 tons.
    • Air discharge temperature from high-pressure compressor can reach 680°C.
    • Maximum pressure inside the engine reaches 30 atmospheres.
    • Maximum flame temperature in the combustion chamber reaches 2300°C.
    • Each high-pressure turbine blade develops 900 hp.
    • Acquisition price of a new engine can exceed 10 million Euros.
    • A shop visit can exceed 1.5 million Euros.

Officinal Maintenance (Of Engines)

  • Engine Maintenance includes work on the Engine after its removal from the Aircraft and usually inside an appropriate Workshop (Engine Workshop).
  • The engine can undergo disassembly of varying complexity degrees, depending on the Workscope to be fulfilled.
  • Engine Maintenance typically includes:
    • Troubleshooting Test, Unit Replacement, Modular Maintenance, PVL (Parts of Limited Life) Replacement, Heavy Maintenance (HM), Repair, Overhaul, Acceptance Testing.

Engine Shop Visit

  • Other lighter Shop Visit types will have shorter partial circuits.
  • Much of the management effort in a Shop Visit is related to Material Management.
  • In a typical Shop Visit bill, 70% are repair and material replacement costs.
  • Typical Shop Visit (Full Performance Restoration, replacement of Life Limit Parts):
    • 55 days of maintenance, 1.3 million USD
    • Disassembly: 5 Days
    • Cleaning, Inspection, Repair, Subcontracts, Material Management: 40 Days
    • Assembly: 9 Days
    • Testing: 1 Day

Example Engine Workshop Layout

  • Includes areas for Plasma Spray, Engine Reception, Engine Disassembly and Assembly, Disassembly Inspection, Subassembly Disassembly and Assembly, Cleaning, Crack Detection, Parts Pool, Preparation, Materials Management and Subcontracts, QECs and Thrust Reversers Overhaul, Reception Inspection, Repair Welding, Material Inspection, Bearing Room, Test Bench, Preparation and Shipping Room, Heat Treatments, Material Reception and Shipping, Electricity, Accessory Gearboxes Provisioning, Shot Peening, Composites, and Painting.

Officinal Maintenance (Of Components)

  • Component Maintenance includes work on Aircraft and Engine Components (Units, Accessories, Etc.) after their removal, usually inside an appropriate Workshop (Component Workshop).
  • Depending on the type of facilities and the Organization its operation, it may be by specialization: Mechanical Components, Hydraulic Components, Pneumatic Components, Electrical Components, Electronic Components (Avionics).
  • Component Maintenance usually includes tasks such as: Visual Inspection, Bench Check (test) - Repair, Overhaul, etc.

Component Workshop Example Layout

  • Includes areas for Mechanics, Hydraulics, Pneumatics, Electrical, Avionics, Emergency, Machine Workshop, Aircraft Maintenance, Surface Treatments, Engine Maintenance, Laboratories and Warehouses, Manufacturers, Suppliers, Specialized Repairers, Customers, Consignment Warehouses, and Pooling.

Supplier Spares Price Lists Example

  • Example information includes supplier code, manufacturer code, part number, description, price, currency, minimum quantity, and lead time.
  • For example:
    • NP165311-5: L/H WINDSHIELD, $10,272.00 USD
    • NP175232-1: L/H SLIDING WINDOW, $9,541.00 USD