TP14038E — Electrical and AvionicsChapter 5 · 150 practice questions

Chapter 5: Electrical, Avionics & Instrumentation

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Overview

This chapter covers the fundamental principles and practices of aircraft electrical, avionics, and instrumentation systems maintenance. It encompasses troubleshooting methodologies, regulatory compliance requirements, inspection procedures, and corrective actions for common electrical and avionics system failures. The material integrates practical troubleshooting techniques with the regulatory framework established by Canadian Aviation Regulations (CARs) and industry standard practices outlined in AC 43.13.

Key Concepts Explained in Detail

Troubleshooting Methodology

Systematic Approach to Electrical Fault Diagnosis

Electrical Troubleshooting — Systematic Progression Electrical Troubleshooting — Systematic Progression 1 Electrical Protections Check circuit breakers and fuses AC 43.13 2 Electrical Power Supply Measure voltage at system terminals Multimeter 3 Connections Inspect for looseness, corrosion, damage CAR 571 4 Wiring Examine for chafing, frayed insulation AC 43.13 5 Components Test individual components (transponder, PFD, etc.) 6 Documentation Record findings in the aircraft logbook CAR 571, 605 Key Regulations • CAR 571 — Maintenance: approved data, release, investigation of tripped breaker before reset • CAR 573 — Modifications/repairs: independent inspection after modification, contact manufacturer if discrepancy • CAR 605 — Continuing airworthiness: safety equipment operational, document corrective actions • AC 43.13 — Acceptable methods: inspect connections, check breakers, clean terminals, replace wires Common faults: corrosion (connectors, terminals) • frayed wiring (replace, never temporary repair) • loose connections (lock, tighten) • intermittent issues (flickering, disconnections)

Electrical system troubleshooting follows a logical progression that begins with the simplest and most probable causes before moving to more complex diagnostics. The fundamental principle is to verify power supply and connections before suspecting component failure.

Initial Troubleshooting Steps:

Tripped Breaker — Investigate Before Reset Circuit Breaker Tripped — Investigation Before Reset STEP 1 — DETECTION Circuit breaker tripped or fuse blown (Common cause of failure) STEP 2 — DIAGNOSIS Investigation before reset Never reset without identifying the cause STEP 3 — CAUSES Temporary overload Short circuit Faulty component STEP 4 — VISUAL AND PHYSICAL INSPECTION Damaged wiring Frayed insulation → Replace the wire Loose connections Visible corrosion → Clean / tighten STEP 5 — DOCUMENTATION Record the findings Logbook CAR 571 / 605 requirement Replacement authorized Identical rating and type Only STEP 6 — RESET Cause identified and fixed Cause not identified RESET AUTHORIZED Functional test required Verify CAR 571 compliance DO NOT RESET Ground the aircraft Defer release (CAR 605) REGULATORY REMINDER • CAR 571: Mandatory investigation before reset • CAR 573: Independent inspection after modification • AC 43.13: Good troubleshooting practices
  • Check circuit breakers and fuses – These are the first line of defense in electrical systems. A tripped breaker or blown fuse indicates either a temporary overload or a persistent fault. Never reset a breaker without investigating the cause.
  • Verify power supply – Measure voltage at the component's input terminals. Low or absent voltage points to supply issues rather than component failure.
  • Inspect connections – Loose, corroded, or damaged connections account for a significant percentage of electrical system failures. Connectors should be visually inspected and physically verified for secure mating.
  • Examine wiring – Look for chafing, frayed insulation, broken conductors, or signs of overheating.

Intermittent Fault Diagnosis

Intermittent problems present unique challenges because they may not be reproducible during ground testing. The key approach involves:

  • Thorough visual inspection of all wiring and connectors in the affected circuit
  • Checking for loose connections that may vibrate or shift during flight
  • Verifying connector integrity – Ensure locking mechanisms function properly
  • Reviewing maintenance logs for previous related issues or modifications
Diagram — Electrical, Avionics & Instrumentation Dépannage électrique et avionique — Approche systématique 1. Symptôme observé 2. Collecte d'informations 3. Causes probables (simples → complexes) 4. Tests et mesures 5. Correction / Remplacement Échec du test Cadre réglementaire • CARs (RAC) • AC 43.13 • Manuel du constructeur • Fiche technique Outils de diagnostic • Multimètre numérique • Testeur de continuité • Oscilloscope • Analyseur de circuits Légende : Symptôme / Échec Test / Correction Analyse / Causes Flux principal Approche logique : du plus simple au plus complexe — Conforme à la norme AC 43.13

Electrical System Components and Maintenance

Electrical and Avionics — Architecture Electrical and Avionics — Architecture ALT / GEN 28V DC BATTERY 24V DC + - MASTER SWITCH MAIN BUS (DISTRIBUTION) GROUND (GND) BRK. AVIONICS (COM, NAV, GPS) BRK. INSTRUMENTS (PFD, MFD, EICAS) BRK. LIGHTING (NAV, STROBE, CABIN) BRK. OTHER SYSTEMS (ELT, GEAR, FLAPS) Current Flow (Educational Animation) Protection (Breaker/Fuse) Component / Equipment

Circuit Breakers and Fuses

Circuit breakers serve as both protective devices and indicators of system health. A tripped breaker demands investigation before resetting. The technician must:

  • Identify the cause of the trip (overload, short circuit, component failure)
  • Document findings in technical records
  • Replace only with components of identical rating and type

Batteries and Power Systems

Battery maintenance requires attention to:

  • Terminal condition – Corrosion indicates potential acid leakage or environmental exposure
  • Voltage levels – Low voltage during engine start can cause system flickering
  • Proper installation – Correct terminal orientation and torque specifications prevent shorts

Wiring and Connectors

Wiring integrity is critical for system reliability. Key maintenance actions include:

  • Replacing damaged wiring – Frayed insulation, chafing, or broken conductors require replacement, not temporary repairs with tape
  • Re-routing harnesses – When chafing against structure is discovered, the harness must be rerouted or protected
  • Replacing corroded connectors – Corrosion degrades electrical performance and reliability
  • Securing connections – Connectors must be properly seated and locked

Avionics Systems

Primary Flight Displays (PFD)

PFD troubleshooting focuses on:

  • Power supply verification – Check circuit breakers and voltage at the display
  • Connection integrity – Loose or corroded connections cause intermittent flickering
  • System calibration – Inaccurate readings may require calibration verification

Autopilot Systems

Autopilot malfunctions often stem from:

  • Wiring and connector issues – Intermittent disconnections frequently result from poor connections
  • Disconnect switch functionality – A stuck switch requires system deferral until repaired
  • Power supply stability – Voltage fluctuations can cause system disengagement

Communication and Navigation Systems

Troubleshooting these systems involves:

  • Audio panel power – Check fuses and circuit breakers first
  • Transponder testing – Requires external power source for ground checks
  • Navigation system calibration – Verify before further diagnosis

Emergency Locator Transmitter (ELT)

ELT maintenance priorities:

  • Battery voltage check – Insufficient power is a common cause of failure
  • Connection verification – Secure all electrical connections
  • Operational testing – Confirm activation and signal transmission

Instrumentation Systems

Pitot-Static Systems

Accurate altitude and airspeed readings depend on:

  • Static port condition – Blockages cause erroneous readings
  • Pitot tube integrity – Ensure unobstructed airflow
  • System leaks – Check for leaks in lines and connections

Altimeter Accuracy

When altimeter readings are incorrect:

  • First check static system for blockages or leaks
  • Verify electrical connections if static system is clear
  • Consider recalibration only after eliminating other causes

Important Regulations and Procedures

Canadian Aviation Regulations (CARs)

CAR 571 – Maintenance and Manufacturing Standards

This regulation governs the standards for maintenance work. Key requirements include:

  • All maintenance must be performed using approved data
  • Functional checks must verify system accuracy and operation
  • Damaged components must be replaced, not temporarily repaired
  • Maintenance releases require documentation of all work performed

CAR 573 – Maintenance Organizations

This regulation addresses organizational requirements:

  • Independent inspections are required after modifications
  • Discrepancies in technical data must be clarified with manufacturers
  • Technical records must document all maintenance actions
  • Non-compliance with airworthiness directives must be reported

CAR 605 – Aircraft Requirements

This regulation covers operational requirements:

  • Safety-critical components must be operational before flight
  • Inoperative equipment may require aircraft deferral
  • Maintenance releases cannot be issued for non-compliant aircraft

AC 43.13 – Acceptable Methods, Techniques, and Practices

This advisory circular provides industry-standard guidance for:

  • Electrical system troubleshooting – Systematic approach to fault diagnosis
  • Connector maintenance – Proper cleaning, inspection, and securing procedures
  • Corrosion prevention – Cleaning and protective coating application
  • Wiring repairs – Replacement criteria and installation standards
  • Battery maintenance – Terminal cleaning and installation procedures

Standard 566 – Maintenance Standards

This standard addresses:

  • Functional check requirements after maintenance
  • System testing under various operating conditions
  • Documentation of test results

Common Relationships Between Concepts

Power Supply and System Performance

The relationship between power quality and system operation is fundamental:

  • Low voltage causes flickering displays, intermittent operation, and system failures
  • Voltage drops during engine start indicate battery condition issues
  • Circuit breaker trips protect against overloads but indicate underlying faults

Connection Integrity and Reliability

Poor connections manifest in predictable ways:

  • Loose connections cause intermittent failures that may appear only during vibration
  • Corroded terminals increase resistance, causing voltage drops and heat generation
  • Damaged connectors lead to complete circuit failure

Regulatory Compliance and Safety

The regulatory framework ensures safety through:

  • Documentation requirements – All maintenance must be recorded for traceability
  • Independent inspections – Verify modification integrity before return to service
  • Airworthiness directive compliance – Mandatory actions for known safety issues
  • Maintenance release procedures – Formal certification of airworthiness

Troubleshooting Progression

Effective troubleshooting follows a logical sequence:

  1. Verify power supply – Check breakers, fuses, and voltage
  2. Inspect connections – Look for loose, corroded, or damaged connectors
  3. Examine wiring – Check for chafing, fraying, or damage
  4. Test components – Only after eliminating supply and connection issues
  5. Document findings – Record all actions and results

Corrosion Management

Corrosion — Effect Chain on Electrical Connections Corrosion — chain of effects on electrical connections TP14038E-EA Ch.5 — Electricity, avionics, and instrumentation CAUSE-EFFECT CHAIN STANDARD RESPONSE — MAINTENANCE ROOT CAUSE Corroded connection Connectors, battery terminals, wire harnesses exposed to moisture PHYSICAL EFFECT Increased resistance at connection point Corrosion creates an insulating barrier that impedes current flow ELECTRICAL CONSEQUENCES Voltage drop + localized heating High resistance causes voltage drop and generates heat OBSERVABLE SYMPTOMS IN FLIGHT / ON GROUND Flickering lights (cabin, navigation) Intermittent autopilot disconnection Complete failure of the affected electrical system Detection STEP 1 — INSPECTION Check for battery acid leaks Visually inspect connectors and terminals for corrosion STEP 2 — CORRECTIVE ACTION Replace corroded connectors Do not clean if replacement is possible — this is the recommended best practice STEP 3 — PROTECTION Apply protective coating To new terminals and connectors in accordance with the maintenance manual STEP 4 — VERIFICATION & DOCUMENTATION Test the circuit — confirm compliance Document the action in the logbook Requirements: RAC 571, 573, 605 — AC 43.13

Corrosion affects electrical systems through:

  • Increased resistance at connection points
  • Potential for complete circuit failure
  • Risk of acid leakage from batteries
  • Progressive damage if not properly treated

The standard response involves:

  • Inspecting for source of corrosion (e.g., battery leaks)
  • Cleaning affected areas
  • Applying protective coatings
  • Replacing severely corroded components

System Interference After Modifications

Modifications can introduce unexpected interactions:

  • Electromagnetic interference between new and existing systems
  • Power supply loading issues from additional equipment
  • Wiring routing conflicts causing chafing or signal degradation
  • Configuration management problems from incomplete documentation

Addressing these requires:

  • Comprehensive functional testing
  • Independent inspection per CAR 573
  • Manufacturer consultation for discrepancies
  • Proper documentation of all changes

Diagram

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