A — Line Maintenance (Aeroplane Piston)Module 7 · 74 practice questions

Module 7A: Maintenance Practices

Includes 2 animated diagrams — view them live in the interactive theory reader.

Torque Application and Thread Types Torque Application and Thread Types TORQUE VALUES & FRICTION EFFECTS Torque = Force × Distance Unit: Newton-metre (N·m) | 1 ft-lb = 1.356 N·m Nominal values applied within tolerance band per AMM Torque Wrench Accuracy — Example Specified: 25 N·m with ±4% wrench accuracy Acceptable range: 24 to 26 N·m Wrench accuracy must be compatible with tolerance Friction Effects on Torque Bearing surface Thread friction Clamping force ~50% of applied torque overcomes thread friction ~30% overcomes bearing surface friction Only ~20% produces clamping force rotation ⚠ If bolt reaches torque but still rotates: Thread damage or galling — slacken, inspect, re-torque Do NOT continue tightening past specified value THREAD TYPES & LUBRICATION FACTOR UNF — Unified Fine 60° thread angle, fine pitch 60° UNC — Unified Coarse 60° thread angle, coarse pitch Lubrication Factor Dry threads Higher torque Lubricated threads Lower torque Use only AMM-approved lubricants Torque–Stretch Relationship Bolt stretches slightly under torque — elastic deformation TORQUE–STRETCH RELATIONSHIP & TORQUE APPLICATION SEQUENCE Torque (N·m) Bolt Stretch (mm) Yield Elastic region (linear) Plastic deformation Torque ∝ Stretch Turn-of-nut method: hand-tight + 3/4 turn (AMM only) Alternative to torque wrench — only if explicitly permitted 1 Clean threads and check for damage (galling, cross-threading, contamination) 2 Apply lubricant if specified by AMM (affects torque reading — use approved type only) 3 Torque smoothly to specified value (within tolerance band, no over-torquing) smooth application
Maintenance Practices Workflow Maintenance Practices Workflow — EASA Part-66 Module 7A Piston Engine Aeroplanes — Human Factors Checkpoints Integrated 1. DOCUMENTATION • Use approved data (AMM, SRM, SB) • Review task card • Verify applicability • Check tooling list 2. TOOLING CONTROL • Select calibrated tools • Verify torque wrench accuracy & cert • FOD control — account for all items 3. TORQUE APPLICATION • Apply N·m or ft-lb (1 ft-lb = 1.356 N·m) • Respect tolerance band • If bolt rotates at torque — inspect threads 4. INSPECTION • Perform GVI • Check for damage, leaks, FOD • Evaluate vs allowable damage limits (SRM) 5. SIGN-OFF • Certify work per Part-66 rights HUMAN FACTORS CHECKPOINTS — INTEGRATED THROUGHOUT THE WORKFLOW Situation Awareness • Stay focused on task • Avoid distractions • Verify aircraft config • Use checklist discipline Communication • Use clear handovers • Read back instructions • Report discrepancies • Ask if uncertain Fatigue & Stress • Recognise fatigue signs • Take breaks when needed • Manage workload • Do not rush tasks Procedure Compliance • Follow AMM exactly • No shortcuts • Use approved data • Record all actions FOD Prevention • Account for all tools • Count rags & parts • GVI before closing • Control loose items Key EASA Part-66 Module 7A Facts: • Torque conversion: 1 ft-lb = 1.356 N·m — always apply within the tolerance band specified in the AMM. • If a bolt reaches specified torque but still rotates: slacken, inspect threads for damage/galling, then re-torque. • Safety wire must exert a tightening force — bend one leg forward over the bolt head, the other backward. • Flexible hoses have a finite shelf life from manufacture date — even if they look good, expired = unserviceable. • Halogen bulbs: never touch with bare hands — skin oils cause hot spots and premature failure. Legend Workflow progression Certification point HF checkpoint

Module 7A: Maintenance Practices — Piston Engine Aeroplanes

1. Module Overview

Module 7A is a foundational module within the EASA Part-66 syllabus for Category A (Piston Engine) certifying staff. It equips the mechanic with the essential knowledge and practical understanding required to perform safe, compliant, and effective line maintenance tasks. The module covers a broad spectrum of topics, from fundamental safety precautions and workshop practices to specific procedures for inspecting, servicing, and rectifying defects on aircraft systems and structures.

The overarching theme is the application of approved data and standard practices to ensure the continued airworthiness of the aeroplane. The module emphasises the legal and procedural framework governing maintenance, the correct use of tools and equipment, and the importance of meticulous documentation and certification.

This study material synthesises the key knowledge areas from the syllabus, focusing on the practical application and theoretical principles that underpin common line maintenance tasks on piston-engine aeroplanes.

2. Key Concepts and Detailed Explanations

2.1 Safety Precautions and Workshop Practices (7A.1, 7A.2)

Safety is the paramount consideration in all maintenance activities. This section covers the fundamental precautions and practices that protect personnel, the aircraft, and the environment.

  • Personal Safety and Personal Protective Equipment (PPE): Before any task, a risk assessment must be performed. The correct PPE must be worn, including safety glasses, gloves, hearing protection, and safety footwear as required by the task and the Safety Data Sheet (SDS) for any chemicals used.
  • Chemical Safety: All chemicals, including solvents, lubricants, and cleaning agents, must be used in accordance with their SDS. This document details the hazards (flammability, toxicity, reactivity), required PPE, first-aid measures, and safe handling and storage procedures. Flammable solvents with a low flash point must be used in well-ventilated areas, away from ignition sources.
  • Foreign Object Damage (FOD) Prevention: FOD is a critical hazard. All tools, rags, and loose parts must be strictly controlled and accounted for. Before closing any panel or cowling, and after completing any task, a thorough general visual inspection (GVI) of the work area must be performed to ensure no items are left behind. This is a fundamental workshop practice.
  • Electrical Safety: Before working on any electrical system or component, the system must be de-energised. This may involve switching off the battery master switch, pulling relevant circuit breakers, or disconnecting the battery. This prevents arcing, personal injury, and damage to sensitive avionics components. When removing electrical connectors, ensure the system is de-energised first to prevent short circuits or pin damage.
  • Hydraulic and Fuel System Safety: Systems may contain residual pressure even when the engine is off. Before disconnecting any hydraulic or fuel line, the system must be depressurised following the AMM procedure. This prevents injury from high-pressure fluid and minimises fluid loss. Fuel and hydraulic fluid are flammable; appropriate precautions must be taken.
  • Propeller Safety: When working on or near a propeller, the ignition must be switched off, and the mixture set to idle cutoff. This prevents the engine from firing if the propeller is rotated, which is a critical personnel safety measure. When rotating the propeller for procedures like a compression test, it must be done in the normal direction of rotation.

2.2 Tools and Equipment (7A.3)

The correct selection, use, and control of tools are essential for quality maintenance.

  • Torque Wrenches: Torque is the application of a rotational force to a fastener. The unit of measurement in the EASA environment is the Newton-metre (N·m). Some manuals may specify torque in foot-pounds (ft-lb). The conversion is: 1 ft-lb = 1.356 N·m.
  • Torque values in maintenance manuals are nominal and must be applied within the tolerance band given in the manual. The accuracy of the torque wrench must be compatible with the specified tolerance. For example, a torque of 25 N·m with a wrench accuracy of ±4% gives an acceptable range of 24 to 26 N·m.
  • If a bolt reaches the specified torque but still rotates, it indicates a problem such as thread damage or galling. The correct action is to slacken the bolt, inspect the threads, and re-torque.
  • Some filters or fasteners may have a "turn-of-the-nut" method specified (e.g., hand-tight then 3/4 turn) as an alternative to a torque wrench. This is only acceptable if explicitly permitted by the AMM.
  • Dial Test Indicator (DTI): A DTI is used to measure small displacements, such as shaft runout. In the EASA environment, it is calibrated in millimetres (mm) or fractions of a millimetre (0.01 mm).
  • Pitot-Static Test Set: A calibrated test set is the only acceptable instrument for applying and measuring pressure when performing functional tests on the pitot-static system. It must be used in accordance with the AMM.
  • Digital Multimeter (DMM): Used for measuring voltage, current, and resistance. For accurate low-resistance measurements, the meter must be zeroed to compensate for lead resistance. The circuit must be de-energised before measuring resistance to prevent damage to the meter and ensure a valid reading.

2.3 Hardware, Materials, and Fasteners (7A.2, 7A.5)

Understanding the properties and correct application of aircraft hardware is fundamental.

  • Lubricants: Aircraft components require specific lubricants (greases and oils) as per the AMM. These are selected for their compatibility with materials, operating temperatures, and performance characteristics. Using an unapproved substitute can cause damage or malfunction. Over-greasing a bearing can cause seal damage; the correct practice is to grease until new grease appears at the bearing edges, then wipe off the excess to prevent dirt accumulation.
  • Locking Devices: These are critical for preventing fastener loosening due to vibration.
  • Safety Wire: Used on bolts, screws, and other fasteners. For two bolts, a single wire is threaded between them. For three or more bolts in a closed pattern (e.g., a triangle), a single wire is threaded through all bolts, typically in a figure-eight configuration. The wire must be installed so that it exerts a tightening force on the fastener. The correct method is to bend one leg forward over the bolt head and the other backward, preventing rotation. A broken safety wire is a defect that must be rectified by re-torquing the fastener and installing new safety wire.
  • Cotter Pins: Used with castellated nuts. The nut is torqued to specification, and the pin is inserted through the nut slots and the bolt hole. The legs are then bent: one forward over the bolt and the other backward over the nut.
  • Lock Washers: Not a substitute for safety wire or cotter pins where those are specified.
  • Flexible Hoses: These have a finite shelf life from the date of manufacture, regardless of storage conditions. A hose that has exceeded its shelf life is unserviceable, even if it appears to be in good condition. Damage that exposes the reinforcement braid is not repairable; the hose must be replaced.
  • O-Rings and Seals: O-rings are single-use items. They must be replaced and lubricated to prevent damage during installation and ensure a proper seal. A missing O-ring on a removed filter must be investigated to prevent foreign object debris (FOD) from entering the system.
  • Tyres: Tyre pressures are specified in the AMM and are critical for safe operation. The specified pressure must be maintained, typically measured at ambient temperature. Over-inflation can cause blowouts; under-inflation causes wear and heat build-up. When disassembling a wheel, the tyre must be deflated in a tyre cage to protect personnel.
  • Halogen Bulbs: Halogen bulbs must not be touched with bare hands. Skin oils create hot spots on the quartz envelope, leading to premature failure. Use a clean cloth or gloves when handling them.

2.4 Inspection and Maintenance Procedures (7A.4, 7A.5, 7A.6)

This section covers the systematic approach to inspecting and maintaining aircraft components.

  • General Visual Inspection (GVI): A visual examination to detect obvious damage, leaks, or discrepancies. Any damage found must be assessed against the AMM or Structural Repair Manual (SRM) allowable damage limits. The correct action is to document and evaluate the damage, not to guess or ignore it.
  • Engine Maintenance:
  • Compression Test: This test checks the condition of the piston rings and cylinder. The propeller must be rotated in the normal direction of rotation to bring the piston to TDC on the compression stroke. This ensures the connecting rod is loaded in compression and the piston rings are forced against the cylinder wall, giving a valid reading. Reverse rotation can cause ring flutter and inaccurate readings.
  • Spark Plug Inspection: The condition of spark plug electrodes indicates combustion quality. Light grey-brown deposits indicate normal combustion. Black, oily, or glazed deposits indicate problems such as oil fouling or incorrect mixture. Serviceable plugs may be cleaned, gapped, and reused per the AMM.
  • Oil Leaks: The AMM defines acceptable leak rates for various components. A small leak may be within limits. The certifying staff must verify the leak rate against the AMM before deciding on a course of action.
  • Propeller Inspection: Nicks and scratches on propeller blades are common. The AMM provides limits for allowable damage. Small nicks within limits may be dressed out with fine files or emery cloth to prevent stress risers. Damage beyond limits requires repair or replacement. Any crack in a propeller spinner is a potential safety issue and must be assessed per the AMM.
  • Control Cables: A broken wire strand protruding from a control cable is a critical defect. It indicates fatigue and potential failure. The correct action is to replace the cable.
  • Corrosion: Superficial corrosion (white powder) on aluminum should be removed using non-metallic abrasive pads (e.g., Scotch-Brite) to avoid scratching the surface. After cleaning, a corrosion inhibitor and primer must be applied. Leaving corrosion is not acceptable, as it can progress.
  • Plexiglass (Transparent Plastics): Cracks in plexiglass can propagate and weaken the window. The AMM provides allowable damage limits; if exceeded, replacement is required. Stop-holes are not an approved repair for plexiglass.
  • Landing Gear:
  • Wheel Bearing Preload: For tapered roller bearings, the correct method is to tighten the nut to a specified torque while rotating the wheel to seat the bearings, then back off to the nearest cotter pin hole that aligns, allowing a small end play. This prevents excessive preload that would cause overheating and premature bearing failure.
  • Retraction Test: Before operating the landing gear for a retraction test, it is mandatory to ensure the area is clear and that down-lock safety pins are installed to prevent accidental gear collapse.
  • Electrical Wiring: Chafed wire insulation is a defect that must be rectified using approved data. Temporary fixes like tape are not acceptable unless specified in the AMM. Repairing aircraft wiring requires following the AMM or Wiring Diagram Manual (WDM) procedures, which typically mandate replacing the wire or using approved splices.

2.5 Documentation and Certification (7A.1, 7A.2)

The legal framework for maintenance is based on approved data and proper certification.

  • Approved Data: All maintenance must be performed in accordance with approved data from the type certificate holder, primarily the Aircraft Maintenance Manual (AMM). Other sources, such as the Illustrated Parts Catalogue (IPC), are used for parts identification. Deviating from approved data is prohibited.
  • Parts Replacement: Replacement parts must be the correct part as specified in the manufacturer's documentation (IPC/AMM). Installing an unapproved part number without engineering approval is prohibited. If a part has a different part number and is not listed as an alternative, it must be returned and the correct one obtained.
  • Certificate of Release to Service (CRS): A CRS must be signed only by certifying staff holding an appropriate Part-66 licence (or equivalent) with the correct aircraft/engine type rating and category privileges, and who is authorised by the Part-145 organisation. The primary record of maintenance performed is the aircraft log book or equivalent maintenance record, which must be signed by the certifying staff.
  • Deferred Defects: A deferred defect must have a valid Minimum Equipment List (MEL) reference to be legally operated. The certifying staff must verify the MEL reference before releasing the aircraft.

3. Important Formulas, Regulations, and Procedures

  • Unit Conversion: 1 ft-lb = 1.356 N·m. For example, 30 ft-lb × 1.356 = 40.68 N·m, rounded to 40.7 N·m.
  • Torque Range Calculation: Acceptable range = Target Torque ± (Target Torque × Accuracy). For 25 N·m with ±4% accuracy: 25 ± (25 × 0.04) = 25 ± 1 = 24 to 26 N·m.
  • Regulatory References:
  • Regulation (EU) No 1321/2014, Annex III (Part-66): Defines the licensing requirements for certifying staff.
  • Regulation (EU) No 1321/2014, Annex II (Part-145): Defines the requirements for maintenance organisations, including the use of approved data (Part-145.A.45) and the certification of maintenance (Part-145.A.50).
  • Part-M: Defines the continuing airworthiness requirements for aircraft, including the use of the MEL and the aircraft technical log.
  • Key Procedures:
  • Safety Wire Installation: Use 6-8 twists per inch, and ensure the wire is routed to tighten the fastener.
  • Cotter Pin Installation: Bend one leg forward over the bolt and the other backward over the nut.
  • Tyre Inflation: Use the AMM-specified pressure, measured at ambient temperature. Use a tyre cage for deflation.
  • Pitot-Static Test: Use a calibrated test set in accordance with the AMM.

4. Common Relationships Between Concepts

  • Safety and Approved Data: All safety precautions are directly linked to the procedures and warnings in the AMM. The AMM is the primary source for both the "how" and the "why" of a task.
  • Tool Use and Accuracy: The accuracy of a tool (e.g., torque wrench, DMM) must be appropriate for the tolerance of the value being measured or applied. Using an inaccurate tool can lead to an incorrect outcome, such as under- or over-torquing a fastener.
  • Inspection and Defect Rectification: The inspection process is about finding discrepancies. The rectification process is about correcting them using approved data. The AMM/SRM defines what is acceptable (within limits) and what is not (beyond limits).
  • Documentation and Airworthiness: The aircraft is not considered airworthy unless all maintenance is properly documented and certified. A CRS is the legal document that releases the aircraft back to service. A deferred defect is only legal if it is documented and has a valid MEL reference.
  • Part Number and Configuration: The correct part number is essential for maintaining the aircraft's configuration. Installing an incorrect part can compromise safety and is a violation of regulations.

5. Typical Exam Focus Points

  • Safety: Questions on chemical safety (SDS), FOD prevention, electrical safety (de-energising), and hydraulic safety (depressurising) are common.
  • Torque: Calculating acceptable torque ranges, converting between ft-lb and N·m, and understanding the correct action if a bolt rotates at specified torque.
  • Locking Devices: The correct methods for safety wiring (especially for multiple bolts) and cotter pin installation.
  • Lubrication: The importance of using the specified lubricant and the correct procedure for greasing (wiping off excess).
  • Inspection: Interpreting spark plug deposits, assessing damage against AMM limits, and understanding the criticality of defects like broken control cable wires.
  • Documentation: The requirements for signing a CRS, the use of approved data, and the correct handling of deferred defects (MEL).
  • Hardware: The shelf life of flexible hoses, the handling of halogen bulbs, and the correct action for a missing O-ring.
  • Engine Practices: The reason for rotating the propeller in the normal direction during a compression test.
  • Landing Gear: The correct preload adjustment for tapered roller bearings and the safety precautions for retraction tests and tyre deflation.

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