Introduction
Aircraft maintenance is a critical discipline that ensures the safety, reliability, and airworthiness of aircraft through systematic inspection, servicing, repair, and overhaul procedures. This comprehensive cheatsheet provides essential information for aircraft maintenance technicians (AMTs), engineers, and aviation professionals responsible for maintaining fixed-wing aircraft and helicopters. It covers key regulations, maintenance types, documentation, common procedures, troubleshooting approaches, and safety practices that form the foundation of professional aircraft maintenance.
Core Concepts of Aircraft Maintenance
Regulatory Framework
- FAA (USA): 14 CFR Part 43 (Maintenance), Part 65 (Certification), Part 91/121/135/145 (Operations/Repair Stations)
- EASA (Europe): Part-145 (Maintenance Organizations), Part-66 (Personnel Licensing), Part-M (Continuing Airworthiness)
- ICAO: Annex 1 (Personnel Licensing), Annex 6 (Operation of Aircraft), Annex 8 (Airworthiness)
- Transport Canada: CAR 571 (Maintenance), CAR 566 (AME Licensing)
Maintenance Personnel Certification
| Authority | License Type | Privileges |
|---|---|---|
| FAA | A&P (Airframe & Powerplant) | Maintain/inspect airframe and engine systems |
| FAA | IA (Inspection Authorization) | Perform annual inspections, approve major repairs/alterations |
| EASA | Part-66 Category A | Line maintenance, simple defect rectification |
| EASA | Part-66 Category B1 | Mechanical systems maintenance |
| EASA | Part-66 Category B2 | Avionics systems maintenance |
| EASA | Part-66 Category C | Base maintenance sign-off |
Types of Maintenance
- Line Maintenance: Routine checks performed between flights (transit, daily, weekly checks)
- Base Maintenance: More extensive scheduled checks requiring hangar facilities (A, B, C, D checks)
- Scheduled Maintenance: Performed at predetermined intervals (flight hours, cycles, calendar time)
- Unscheduled Maintenance: Performed in response to discrepancies, failures, or abnormal conditions
- Preventive Maintenance: Actions to prevent failures (lubrication, adjustment, cleaning)
- Corrective Maintenance: Actions to restore systems to serviceable condition after failure
- Predictive Maintenance: Condition-monitoring to predict failures before they occur
Maintenance Documentation
Essential Documents
| Document | Purpose | Content |
|---|---|---|
| Aircraft Maintenance Manual (AMM) | Primary reference for maintenance procedures | Step-by-step instructions for maintenance tasks |
| Illustrated Parts Catalog (IPC) | Parts identification | Exploded views, part numbers, assembly relationships |
| Structural Repair Manual (SRM) | Repair instructions | Approved methods for structural repairs |
| Wiring Diagram Manual (WDM) | Electrical system reference | Wiring schematics, connector pinouts |
| Component Maintenance Manual (CMM) | Component-level maintenance | Detailed component overhaul procedures |
| Service Bulletins (SB) | Manufacturer recommendations | Improvements, modifications, or safety issues |
| Airworthiness Directives (AD) | Mandatory requirements | Safety-related requirements from authorities |
| Minimum Equipment List (MEL) | Operational guidance | Items that may be inoperative for flight |
| Task Cards | Work instructions | Specific maintenance task steps and sign-offs |
Maintenance Records Requirements
- FAA: Records must include description of work, date, name, signature, certificate number
- EASA: Records must be clear, accurate, maintained for specified periods
- Required Retention Periods:
- 1 year for routine maintenance records
- 2 years for detailed maintenance records
- Life of the aircraft for life-limited parts, major repairs/alterations
Electronic Documentation Systems
- Aircraft Technical Publisher (ATP)
- Boeing Maintenance Performance Toolbox
- Airbus ADOC/AirN@v
- Aviation Maintenance & Engineering Software (AMES)
Aircraft Maintenance Checks
Commercial Aircraft Check Schedule
| Check | Typical Interval | Downtime | Scope |
|---|---|---|---|
| Transit Check | Between flights | 30-60 mins | Visual inspection, fluid levels, obvious damage |
| Daily Check | 24-48 hours | 1-3 hours | Basic systems checks, fluid levels, security of components |
| A Check | 400-600 flight hours | 6-24 hours | General inspection of systems and components |
| B Check | 6-8 months (often integrated into A checks) | 1-3 days | More detailed inspection of systems and structure |
| C Check | 15-24 months / 4,000-6,000 flight hours | 1-2 weeks | Detailed inspection of most aircraft components |
| D Check / Heavy Maintenance Visit | 6-12 years | 1-2 months | Major structural inspection, overhaul of components |
General Aviation Inspection Requirements
- Annual Inspection: Required every 12 calendar months
- 100-Hour Inspection: Required for commercial operations after every 100 hours
- Progressive Inspection: Alternative to annual/100-hour inspection divided into smaller segments
- Condition Inspection: Required annually for experimental aircraft
Safety Practices & FOD Control
Personal Safety
- PPE Requirements: Safety glasses, hearing protection, gloves, steel-toed boots
- Fall Protection: Safety harnesses, guardrails, proper ladder usage
- Confined Space: Proper ventilation, buddy system, permits
- Chemical Handling: MSDS/SDS reference, proper storage, spill procedures
Aircraft Protection
- Surface Protection: Wing covers, pitot covers, fuselage protective mats
- Grounding: Static discharge procedures
- Tool Control: Shadow boards, tool check-in/check-out systems, inventory
- Component Protection: Caps, plugs, covers for open lines/ports
FOD (Foreign Object Debris/Damage) Prevention
- Housekeeping: Clean as you go, regular area sweeps
- FOD Walks: Systematic inspection of ramp/hangar areas
- Tool Accountability: Tool inventory before/after maintenance
- FOD Containers: Designated disposal containers
- FOD Critical Areas: Engine inlets, flight controls, gear mechanisms
Common Maintenance Tasks & Procedures
Engine Maintenance
| Task | Key Points | Common Issues |
|---|---|---|
| Oil Change | Proper disposal, correct oil grade, filter inspection | Metal contamination, incorrect fill level |
| Borescope Inspection | Engine port access, systematic inspection pattern | Blade damage, combustion deposits, FOD |
| Compression Check | Differential pressure test, cylinder sequencing | Low compression, leaking valves |
| Fuel System Checks | Drain points, contamination checks, filter inspection | Water contamination, clogged filters |
| Ignition System | Timing checks, gap settings, harness condition | Lead fouling, worn harness, timing issues |
Airframe Maintenance
| Task | Key Points | Common Issues |
|---|---|---|
| Skin Inspection | Lighting, visual aids, mapping defects | Corrosion, stress cracks, dents |
| Corrosion Treatment | Identification, removal, treatment, protection | Hidden corrosion, improper treatment |
| Control Surface Rigging | Deflection measurement, cable tension | Binding, excessive play, improper tension |
| Landing Gear Service | Strut extension, tire condition, brake wear | Strut leaks, uneven tire wear, overheated brakes |
| Structural Fasteners | Torque values, safety methods, replacement criteria | Loose fasteners, improper torque, missing safety wire |
Avionics Maintenance
| Task | Key Points | Common Issues |
|---|---|---|
| EFIS Testing | Self-test procedures, display quality | Display failures, data inconsistencies |
| Radio Checks | VSWR testing, transmission/reception quality | Poor transmission, receiver sensitivity |
| Navigation System | Database currency, signal quality | Outdated databases, antenna issues |
| Autopilot System | Servo operation, control checks | Servo slippage, improper engagement |
| Pitot-Static System | Leak testing, instrument correlation | Leaks, blocked ports, instrument errors |
Hydraulic System Maintenance
| Task | Key Points | Common Issues |
|---|---|---|
| Fluid Level Checks | Proper reservoir level, correct fluid type | Contamination, incorrect level |
| Leak Detection | Systematic inspection, cleanliness | Seeping fittings, damaged O-rings |
| Filter Inspection | Contamination check, bypass indication | Clogged filters, metal contamination |
| Pressure Checks | Test points, pressure gauges | Low pressure, pump issues |
| Actuator Service | Freedom of movement, seal condition | Internal leakage, binding |
Critical Measurement Reference
Torque Values
| Fastener Size | AN Bolts (inch-lbs) | MS Bolts (inch-lbs) |
|---|---|---|
| #8 (4-40) | 12-15 | 15-18 |
| #10 (4-40) | 20-25 | 25-30 |
| 1/4″ | 80-100 | 100-140 |
| 5/16″ | 160-190 | 220-300 |
| 3/8″ | 240-290 | 400-500 |
| 7/16″ | 400-480 | 600-730 |
| 1/2″ | 480-690 | 900-1,100 |
Electrical Values
| Parameter | Typical Range | Notes |
|---|---|---|
| Battery Voltage (Lead Acid) | 12V system: 11.5-14.3V | <10.5V indicates failed battery |
| Battery Voltage (Lithium) | 12V system: 12.8-13.2V | Temperature compensation required |
| Bus Voltage | 28V system: 27.5-29.5V | <25V indicates charging issue |
| Generator Output | 28V system: 28-29.5V, 0-max rated amps | Fluctuations indicate regulator issues |
| Starter Current | 200-400A (small aircraft), 400-1000A (larger) | Higher current indicates mechanical issue |
Fluid Specifications
| System | Common Specifications | Notes |
|---|---|---|
| Engine Oil (Piston) | SAE 15W-50, SAE 20W-50, MIL-L-22851 | Refer to engine manual for grade |
| Engine Oil (Turbine) | MIL-PRF-23699, MIL-PRF-7808 | Type depends on engine model |
| Hydraulic Fluid | MIL-PRF-5606, MIL-PRF-83282, MIL-PRF-87257 | Never mix different types |
| Coolant | MIL-C-38276, ASTM D3306 | Use inhibited ethylene glycol |
| Grease | MIL-G-81322, MIL-G-23827, MIL-G-21164 | Application-specific |
Control Surface Deflection
| Surface | Typical Range | Measurement Method |
|---|---|---|
| Ailerons | ±15-25° | Protractor at trailing edge |
| Elevator | 25° up, 15° down | Protractor at trailing edge |
| Rudder | ±25-30° | Protractor at trailing edge |
| Flaps | 0-10-20-30-40° (varies by aircraft) | Protractor at trailing edge |
| Trim Tabs | ±10-25° | Protractor at trailing edge |
Troubleshooting Methodologies
Systematic Approach to Troubleshooting
- Gather Information: Collect crew reports, maintenance history, symptoms
- Verify the Problem: Reproduce the issue if possible
- Isolate the System: Determine which system/subsystem is affected
- Identify Probable Causes: Use troubleshooting trees, experience
- Test Hypotheses: Check each potential cause
- Implement Solution: Repair or replace components
- Verify Repair: Operational test to confirm problem is resolved
- Document Actions: Complete maintenance records
Common Troubleshooting Tools
| Tool | Applications | Notes |
|---|---|---|
| Multimeter | Voltage, continuity, resistance measurement | Essential for electrical troubleshooting |
| Borescope | Internal visual inspection | Engine, inaccessible areas |
| Pressure Gauges | Hydraulic, pneumatic, fuel system testing | System-specific calibration |
| Vibration Analyzer | Rotating component inspection | Bearing failure prediction |
| Ultrasonic Tester | Leak detection, bearing analysis | Non-invasive testing |
| Logic Analyzer | Digital system troubleshooting | Avionics signal analysis |
| Thermal Imaging | Hot spots, electrical issues | Preventive maintenance |
Engine Troubleshooting Guide
| Symptom | Possible Causes | Investigation Steps |
|---|---|---|
| Low Power Output | Ignition timing, fuel delivery, compression | Check magnetos, fuel pressure, compression test |
| Excessive Oil Consumption | Worn rings, valve guides, oil leaks | Compression test, borescope inspection, leak check |
| Rough Running | Ignition issues, fuel contamination, valve issues | Magneto check, fuel quality, cylinder balance |
| Metal in Oil | Internal component wear, bearing failure | Spectrographic analysis, filter inspection, borescope |
| High EGT/CHT | Improper mixture, ignition timing, cooling issues | Check baffling, mixture settings, ignition timing |
Hydraulic System Troubleshooting
| Symptom | Possible Causes | Investigation Steps |
|---|---|---|
| Slow Operation | Low fluid, pump issues, internal leakage | Check fluid level, pressure test, component isolation |
| Noisy Pump | Cavitation, air in system, pump wear | Check fluid level, bleed system, pump inspection |
| System Overheating | Relief valve issues, excessive demand | Check relief valve, pressure, duty cycle |
| Intermittent Operation | Air in system, electrical control issues | Bleed system, check electrical controls |
| External Leakage | Loose fittings, damaged lines, seal failure | Visual inspection, pressure test, component isolation |
Electrical System Troubleshooting
| Symptom | Possible Causes | Investigation Steps |
|---|---|---|
| Low Voltage | Generator failure, regulator issues, high demand | Load test, voltage drop test, regulator check |
| Circuit Breaker Trips | Short circuit, overload, CB failure | Isolation testing, load measurement, wiring inspection |
| Intermittent Failure | Loose connections, thermal issues, vibration | Wiggle test, thermal cycling, connection inspection |
| Radio Noise | Ground issues, alternator whine, shielding failure | Bond testing, filter check, shielding integrity |
| Battery Rapid Discharge | High parasitic load, battery failure, charging issue | Load test, parasitic drain test, charging system check |
Special Maintenance Procedures
NDT (Non-Destructive Testing) Methods
| Method | Applications | Detects |
|---|---|---|
| Dye Penetrant | Surface inspection of non-porous materials | Surface cracks, porosity |
| Magnetic Particle | Ferromagnetic material inspection | Surface/near-surface defects |
| Eddy Current | Conductive material inspection | Surface/near-surface defects, thickness |
| Ultrasonic | Internal structure inspection | Internal flaws, delamination, thickness |
| Radiography | Internal structure visualization | Internal defects, assembly verification |
Corrosion Identification & Treatment
| Corrosion Type | Appearance | Treatment |
|---|---|---|
| Surface | Dulling, powdery deposits | Clean, treat with conversion coating, prime/paint |
| Pitting | Small holes/pits in material | Remove to clean metal, evaluate depth, repair/replace |
| Exfoliation | Lifting/flaking of layers | Remove affected area, may require replacement |
| Intergranular | Often invisible until structural failure | Requires specialized NDT, often requires replacement |
| Filiform | Worm-like traces under paint | Remove paint, treat corrosion, apply proper primer/paint |
| Galvanic | Occurs between dissimilar metals | Clean, isolate dissimilar metals, apply proper finish |
Weight & Balance Procedures
- Aircraft Preparation: Empty fuel (or note quantity), proper configuration
- Weighing Equipment: Calibrated scales, proper positioning
- Weighing Process: Level aircraft, record individual point weights
- Calculations: Determine empty weight and moment arm
- Documentation: Update weight and balance records, equipment list
Composite Repair
| Damage Type | Repair Approach | Critical Factors |
|---|---|---|
| Delamination | Injection repair, vacuum bagging | Complete resin penetration, proper cure |
| Surface Damage | Scarf/taper repair, ply replacement | Correct ply orientation, overlap distance |
| Puncture | Core replacement, laminate restoration | Moisture removal, structural continuity |
| Heat Damage | Assessment, potential replacement | Often requires ultrasonic inspection |
| Impact Damage | Visual/NDT assessment, repair based on depth | Hidden damage assessment critical |
Maintenance Safety & Human Factors
Critical Safety Practices
- Lockout/Tagout: Secure systems from unexpected energization
- Confined Space Entry: Proper ventilation, monitoring, rescue plan
- Fall Protection: Appropriate harnesses, secure tie-off points
- Hazardous Materials: Proper handling, storage, disposal
- Fire Safety: Extinguisher types, evacuation procedures
Human Factors in Maintenance (PEAR Model)
- People: Physical capabilities, psychological factors, physiological state
- Environment: Physical (lighting, noise, temperature), organizational culture
- Actions: Steps, procedures, documentation
- Resources: Tools, equipment, time, personnel
The “Dirty Dozen” Maintenance Human Factors
- Lack of Communication: Clear handovers, shift changes
- Complacency: Following procedures even for routine tasks
- Lack of Knowledge: Proper training, reference to manuals
- Distraction: Work area discipline, focus on task
- Lack of Teamwork: Coordination, mutual verification
- Fatigue: Recognize signs, proper rest
- Lack of Resources: Proper tools, adequate time
- Pressure: Resist rushing, safety prioritization
- Lack of Assertiveness: Speaking up about concerns
- Stress: Stress management techniques
- Lack of Awareness: Situational awareness, big picture
- Norms: Avoiding normalization of deviance
Resources for Further Learning
Technical Publications
- FAA Advisory Circulars (especially AC 43.13-1B/2B)
- Aircraft-specific maintenance manuals
- Engine manufacturer service documents
- Component maintenance manuals
Professional Organizations
- Aircraft Maintenance Technicians Association (AMTA)
- Professional Aviation Maintenance Association (PAMA)
- National Business Aviation Association (NBAA)
- International Air Transport Association (IATA)
Training Resources
- FAA Maintenance Handbook
- Aircraft Technical Book Company publications
- Manufacturer training programs
- Aviation Maintenance Technician Series (Dale Crane)
Online Resources
- FAA Safety Team (FAAST)
- Aviation Maintenance Technology Magazine
- Aircraft Maintenance Technology Magazine
- Regulatory authority websites (FAA, EASA, TCCA)
Quick Tips for Maintenance Professionals
- Always consult current maintenance manuals before performing tasks
- Use the proper tools specified for each job
- Document all work completely, accurately, and legibly
- When in doubt, ask a more experienced technician or supervisor
- Maintain calibration on all precision tools and test equipment
- Practice methodical troubleshooting rather than parts-swapping
- Stay current with service bulletins and airworthiness directives
- Recognize and manage fatigue and stress
- Use checklists for critical tasks
- Develop a personal commitment to safety and quality