SkyLicence
Chapter XIII

TP14038E — Airframe Review

SkyLicence study guide with diagrams.

Overview

Airframe Structures and Systems — Overview Airframe and Systems — Overview PRIMARY STRUCTURE Fuselage, Wings, Empennage FLIGHT CONTROLS Surfaces, Cables, Linkages, Hinges FUEL SYSTEM Tanks, Lines, Fire Safety GEAR & HYDRAULICS Retraction, Brakes, Fluid, Lines INSPECTION & COMPLIANCE CAR 571/573 • AC 43.13 • Sign-off Source: TP14038E — AME Study Guide

This chapter covers the fundamental principles of airframe structures and systems maintenance, focusing on inspection procedures, damage assessment, repair techniques, and regulatory compliance. The material addresses structural integrity, fuel systems, control surfaces, landing gear, and composite materials, emphasizing the critical relationship between maintenance actions and continued airworthiness under Canadian Aviation Regulations (CARs).

Key Concepts Explained

Structural Inspection Principles

Visual Inspection Fundamentals

Visual inspection remains the primary method for detecting surface anomalies including dents, corrosion, cracks, and delamination
Environmental conditions significantly affect inspection quality; inspections should be conducted under optimal lighting and weather conditions as per CAR 571.03
Systematic inspection patterns ensure complete coverage of all structural elements

Damage Assessment Categories

Surface damage: Dents, scratches, paint chips that may indicate underlying issues
Structural damage: Cracks, corrosion, delamination affecting load-bearing capability
Hidden damage: Fatigue cracks, internal corrosion requiring specialized detection methods

Critical Inspection Areas

Critical Inspection Areas of the Airframe Critical Cell Inspection Zones Plan View — Low-Wing Monoplane Aircraft INSPECTION ZONES LEGEND: Wing-fuselage joints Stress concentration — fatigue and cracking Leading edges Impacts, corrosion and erosion Riveted joints Corrosion and integrity of fasteners Control surface hinges Wear and freedom of movement Rudder control linkages REGULATORY REFERENCES • RAC 571 — Airworthiness standards • RAC 573 — Maintenance documentation CRITICAL POINT Fatigue initiates at stress concentration points TP14038E-AF — Chapter 3: Cell structures and systems — Critical inspection zones
Wing-fuselage joints represent stress concentration points where fatigue typically initiates
Leading edges are susceptible to impact damage and corrosion
Riveted joints require careful examination for corrosion and fastener integrity
Control surface hinges and linkage points demand regular inspection for wear and freedom of movement
Diagram — Airframe Structures & Systems Airframe Structures & Systems — Inspection & Damage Assessment Flow AIRCRAFT STRUCTURAL CROSS-SECTION Fuselage Skin Panel Stringers & Frames (Primary Structure) D Dent Crack Corrosion COMPOSITE LAMINATE STRUCTURE Ply 1 (0°) Ply 2 (45°) Ply 3 (90°) Ply 4 (-45°) Ply 5 (0°) Delamination INSPECTION DECISION FLOW Visual Inspection Damage Detected? Yes Assess Damage Within Limits? No Return to Service Yes No Repair Required Regulatory Compliance (CARs) CAR 571 — Maintenance & Continuing Airworthiness CAR 573 — Airworthiness Directives & Service Bulletins Legend Primary Structure (Stringers/Frames) Composite Laminate Piles Damage Indicators (Dent/Crack/Corrosion) Technician d'Entretien d'Aéronefs (TEA) — Airframe Structures & Systems — TC Approved Training Material

Corrosion Management

Corrosion progression and control Corrosion Progression and Management AME Training — Airframe Structures — Transport Canada (CAR 571 / AC 43.13) 1. MOISTURE / ELECTROLYTE • Water, humidity, condensation • Electrolyte (salts, pollutants) • Retention areas: seals, leading edges, fuselage bottoms Favorable conditions: • Cracks, delamination, seal defects • Lack of drainage / ventilation Progression 2. SURFACE CORROSION • Localized pitting • Loss of protection (clad, paint, anodizing) Aggravation 3. INTERGRANULAR CORROSION • Propagation along grain boundaries — loss of strength ⚠ CRITICAL METAL MICRO-STRUCTURE Normal state Intact grain boundaries Corroded Attacked grain boundaries Intergranular corrosion follows grain boundaries — invisible on surface, detectable by ultrasound / radiography. → Assess depth before repair TREATMENT CHAIN 1 CLEAN Degrease, brush, remove corrosion products 2 TREAT Apply corrosion inhibitor (chemical conversion) 3 PROTECT Primer + topcoat paint per manufacturer specifications REGULATORY REMINDER CAR 571 — Airworthiness: Assess the extent and depth of corrosion before repair CAR 573 — Documentation: Any finding must be documented before return to service AC 43.13 — Practices: Cleaning, treatment and protection per approved methods INSPECTION PROCEDURE 1 Initial assessment Extent and severity of damage 2 Manual reference Manufacturer allowable limits 3 Inspect underlying structure Check for hidden damage 4 Reporting and documentation In accordance with CAR 573 Transport Canada — AME Training — Airframe Structures and Systems — Corrosion: progression and management

Types and Detection

Surface corrosion appears as pitting, discoloration, or blistering of paint
Intergranular corrosion can occur at fastener holes and joints
Galvanic corrosion develops between dissimilar metals

Assessment Protocol

28.Evaluate corrosion extent to determine appropriate repair method
29.Remove corrosion completely and inspect underlying structure
30.Treat affected area according to manufacturer specifications
31.Document findings and repairs per CAR 573 requirements

Prevention Measures

Regular cleaning and protective coating maintenance
Proper drainage provisions in structural design
Application of corrosion-inhibiting compounds

Structural Damage Evaluation

Structural damage assessment flow Structural Damage Assessment Flow RAC 571 — RAC 573 — AC 43.13 STEP 1 — IDENTIFY Visual inspection Corrosion, crack, dent, delamination STEP 2 — MEASURE Extent and depth Gauges, ultrasonics, detailed inspection STEP 3 — COMPARE SRM / Manual limits Manufacturer allowable limits WITHIN LIMITS? YES NO STEP 4A — CLASSIFY Allowable damage Minor repair / none STEP 5A — REPAIR / DOCUMENT Approved repair AC 43.13 Documentation RAC 573 STEP 4B — CLASSIFY Non-allowable damage Major repair required STEP 5B — REPAIR / DOCUMENT Ground if airworthiness is compromised Release after RAC 573 compliance RELEASED Signed and compliant References: RAC 571.02, RAC 571.10, RAC 573, AC 43.13, Standard 566

Dent Assessment Criteria

Small circular dents with cracked paint may indicate impact damage requiring detailed inspection
Dents must be evaluated against acceptable limits specified in maintenance manuals
Underlying structure inspection is mandatory before patch repairs

Crack Detection and Evaluation

Fatigue Cracking — Detection and Evaluation Fatigue Cracking — Detection and Evaluation Stress Concentration Points Wing Root Max bending zone Crack Spars Crack Riveted Joints Crack Propagation Repeated cyclic stress → initiation and growth Ultrasonic Detection — Subsurface Cracks Cross-section Structure Crack subsurface PROBE Echo Display Crack peak Estimated depth: 2.5 mm ✓ Detects surface-invisible cracks — most effective method Evaluation — Primary Structural Elements Crack Detected Ultrasonic / visual inspection (CAR 571.02) Structural Evaluation Consult manufacturer manual Allowable limits (AC 43.13) Decision Primary element? Limits exceeded? GROUNDING IMMEDIATE (CAR 571.10) YES Approved Repair CAR 573 documentation Release before return to service NO ⚠ Primary structural elements: spars, ribs, pressurized skin, critical frames Any crack on a primary element compromises airworthiness → immediate grounding (CAR 571.10) | Documentation required (CAR 573)
Fatigue cracks typically develop at stress concentration points
Ultrasonic testing is most effective for detecting subsurface fatigue cracks
Cracks in primary structural members require immediate grounding and assessment

Composite Material Damage

Composite Delamination — Layer Separation Composite Delamination — Layer Separation TP 14038E-AF — Chapter 3: Cell Structures and Systems Cross-section of a composite laminate PLY 1 PLY 2 PLY 3 PLY 4 PLY 5 PLY 6 PLY 7 DELAMINATION ZONE Enlarged view Structural ply Separation / void DEFINITION Separation of layers (plies) in a composite material. The plies peel apart and lose their structural bond. STRUCTURAL IMPACT • Loss of mechanical strength • Reduced stiffness • Propagation under stress • Even in non-structural areas REGULATORY REQUIREMENT • Expert assessment required • Manufacturer procedures • RAC 573 documentation • Release before return to service DETECTION METHODS: Visual inspection (edge, surface) • Tap test (percussion) • Ultrasonics • Thermography ⚠ RISK: Silent propagation under load ■ Normal ply ■ Delaminated zone (void) → Direction of separation propagation
Delamination in composite structures requires expert evaluation
Manufacturer repair procedures must be strictly followed
Non-structural delamination still requires proper documentation and repair

Fuel System Maintenance

Fuel system safety zones Fuel System Safety Zones Ventilation, drainage, grounding, vapor risks and leak control — AME Training Transport Canada WING TANK Aviation fuel (AvGas / Jet A) Fuel level Vapors Flow Ventilation Flow Ventilation SUMP Tray Drainage Water/sediment check GROUND Grounding Prevents sparks ⚡ Risk eliminated ⚠ HAZARD ZONE Flammable vapors No ignition sources No smoking Diffusion LEAK CONTROL Pressure test Reliable method Visual inspection Signs of seepage LEAK PROCEDURE 1. Report immediately 2. Ground the aircraft 3. Fire hazard 4. Document (CAR 573) REGULATORY REFERENCES CAR 571 — Airworthiness CAR 573 — Documentation AME Training — Transport Canada — Fuel systems: safety and maintenance

Leak Detection and Safety

Pressure testing is the most reliable method for detecting fuel system leaks
Fuel leaks pose significant fire hazards requiring immediate grounding
All ignition sources must be eliminated during fuel system inspections

System Integrity

Blocked static ports affect altitude and airspeed readings
Fuel system modifications must be documented and assessed per CAR 573
Proper documentation of all fuel system repairs is mandatory

Control Surface Systems

Flight-control continuity check Flight Control Continuity Mechanical chain: stick → cables → pulleys → control surface COCKPIT Movement Stick / Column Freedom: full travel CABLE AND PULLEY TRANSMISSION Pulley Pulley Pulley Pulley Cable tension: check deflection (Standard 566) Excessive slack → control imprecision CONTROL SURFACE UPPER STOP LOWER STOP Deflection Hinge Max play: per manufacturer PRE-FLIGHT CHECKS (RAC 571) Free movement of control surfaces through full range Inspect cables, pulleys, and attachment points first Mechanical continuity: stick → cables → pulleys → control surface COMMON CAUSES OF RESTRICTION • Corrosion or obstruction of hinges • Incorrect control cable tension • Mechanical obstruction from debris or ice REGULATORY REFERENCES RAC 571 — Airworthiness Standard 566 — Hinge play

Inspection Requirements

Control surfaces must move freely through full range of motion
Excessive play in control linkages requires investigation per maintenance manual
Hinge points are critical inspection areas for corrosion and obstruction

Troubleshooting Sequence

69.Check control cables for proper tension and condition
70.Inspect hinge points for corrosion or obstruction
71.Verify control linkage integrity
72.Refer to maintenance manual for specific tolerances

Landing Gear Systems

Hydraulics and landing gear Hydraulics and Landing Gear RESERVOIR Hydraulic Hydraulic fluid Min. level Return PUMP Hydraulic motor Suction Pressure VALVES Selector Control ACTUATOR Actuator body Rod Landing gear attachment LOCKING Locking extension (down) Locking retraction (up) Hooks actuated by springs EXTENSION / RETRACTION TROUBLESHOOTING 1. Check hydraulic fluid level 2. Inspect torque links for wear 3. Check brake lines for chafing 4. Remove line if external wear 5. Consult manual for limits Ref. manual REGULATORY REFERENCES AND BEST PRACTICES CAR 571 Airworthiness standards CAR 573 Maintenance documentation Std 566 Hinge clearance limits AC 43.13 Maintenance practices CAR 605.12 Weight and balance Pressure line Return line Suction Pump rotation

Hydraulic System Considerations

Low hydraulic fluid level is a common cause for incomplete retraction
Hydraulic line wear requires removal for thorough inspection
Brake line damage must be addressed immediately per CAR 571

Component Wear Assessment

Torque link wear must be compared to maintenance manual limits
Uneven tire wear indicates alignment issues requiring correction
Landing gear retraction testing verifies system functionality

Important Regulations and Procedures

Canadian Aviation Regulations (CARs)

CAR 571 - Maintenance Standards

CAR 571.02: Thorough inspections required for continued airworthiness
CAR 571.03: Inspections under optimal conditions
CAR 571.10: Defect reporting and documentation requirements
All defects must be reported and addressed properly
Corrosion findings require assessment and approved repair procedures

CAR 573 - Maintenance Release Requirements

Signed maintenance release mandatory before returning aircraft to service
Documentation must include detailed repair descriptions
All modifications require proper evaluation and documentation
References to applicable maintenance manuals must be included

Standard 566 - Control Surface Limits

Play in control surface hinges must be assessed against manufacturer limits
Exceeding specified tolerances requires corrective action

Advisory Circulars

AC 43.13 - Acceptable Methods, Techniques, and Practices

Hammer and dolly method for aluminum skin dent repair
Proper corrosion assessment and remediation procedures
Hydraulic system inspection standards
Cable system inspection requirements
Safety protocols for fuel system work

Maintenance Documentation Requirements

Pre-Release Checklist

All repairs properly documented
Compliance with regulatory standards verified
Maintenance release signed by authorized technician
References to applicable maintenance manuals included

Modification Documentation

Previously undocumented modifications must be escalated to maintenance manager
Impact on airworthiness must be assessed
CAR 573 compliance for all modifications

Common Relationships Between Concepts

Damage Assessment Flow

118.Discovery Phase
Visual detection of anomaly (dent, crack, corrosion, delamination)
Initial assessment of severity and location
121.Evaluation Phase
Compare to acceptable limits in maintenance manual
Determine if underlying structure inspection is required
Assess impact on structural integrity
125.Action Phase
Ground aircraft if safety-critical component affected
Report findings to supervisor/maintenance manager
Document findings per CAR 571.10
129.Repair Phase
Follow manufacturer-approved procedures
Use specified materials and fasteners
Verify repair meets airworthiness standards
133.Release Phase
Complete maintenance release documentation
Include references to applicable manuals
Ensure CAR 573 compliance

Safety-Critical Relationships

Structural integrity ↔ Airworthiness: Any compromise to load-bearing structures affects flight safety
Corrosion ↔ Structural degradation: Unaddressed corrosion leads to progressive weakening
Control surface freedom ↔ Flight control: Restricted movement compromises aircraft control
Fuel system integrity ↔ Fire safety: Leaks create immediate fire hazards
Documentation ↔ Regulatory compliance: Proper records ensure traceability and accountability

Inspection Priority Matrix

Troubleshooting Logic

Troubleshooting Logic — Anomaly Decision Tree Troubleshooting Logic — Anomaly Decision Tree Anomaly Detected Is the component critical for safety? YES NO GROUND IMMEDIATELY CAR 571.10 Does the damage exceed acceptable limits? YES NO REPAIR / REPLACE AC 43.13 DOCUMENT AND MONITOR CAR 573 Is the repair procedure specified? YES NO FOLLOW MANUFACTURER'S MANUAL Maintenance manual CONSULT MANUFACTURER Approval required Are the materials available? YES NO PROCEED WITH REPAIR Release CAR 573 ORDER MATERIALS AOG if necessary Active analysis path TP14038E-AF ch3 — CAR 571/573 · AC 43.13 · Standard 566

When encountering anomalies, the technician should follow this decision tree:

147.Is the component safety-critical?
Yes: Ground aircraft immediately
No: Continue with assessment
150.Does the damage exceed allowable limits?
Yes: Repair or replace per manual
No: Document and monitor
153.Is the repair procedure specified?
Yes: Follow manufacturer instructions
No: Consult manufacturer for approved methods
156.Are proper materials available?
Yes: Proceed with repair
No: Source approved materials before proceeding

This systematic approach ensures compliance with CARs and maintains aircraft airworthiness while promoting safety and regulatory adherence.

Chapter 12Engine Installation, Fire Protection & Troubleshooting

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