FAA Airframe Written TestChapter 9 · 50 practice questions

Chapter 9: Communication, Light Signals, and Runway Lighting Systems

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Chapter: Communication, Light Signals, and Runway Lighting Systems

Overview

This chapter covers the aircraft lighting systems essential for safe operation, including position (navigation) lights, anti-collision lights (beacons and strobes), landing and taxi lights, and instrument panel lighting. It also addresses the regulatory requirements governing these systems, systematic troubleshooting methodologies, and the maintenance standards prescribed by FAA regulations and advisory circulars. The material emphasizes the critical relationship between electrical system integrity, regulatory compliance, and airworthiness.

Key Concepts

1. Aircraft Lighting System Classifications

Aircraft Lighting Classifications - Position, Anti-Collision, Landing, Taxi, and Instrument Panel Lights Aircraft Lighting Classifications — FAA A&P Prep RED L GREEN R WHITE BEACON LANDING LIGHT TAXI PANEL POSITION (NAV) LIGHTS Left wingtip — Red Right wingtip — Green Tail — White Required for night operations ANTI-COLLISION LIGHTS Rotating beacon (red) Strobe lights (white) Required day AND night No MEL relief for Part 91 14 CFR §91.209 LANDING / TAXI / PANEL Landing lights (nose) Taxi lights (nose gear) Instrument panel lights AC 43.13-1B Chapter 11 Landing lights: 14 CFR §91.205(b)(11) KEY REGULATIONS 14 CFR §91.209 — Anti-collision 14 CFR §91.205 — Equipment req. AC 43.13-1B Ch. 11 — Lighting FAA ACS — Airworthiness Position lights: steady burn LIGHT COLOR KEY Red — Left wing, beacon Green — Right wing White — Tail, strobes SkyLicense FAA A&P Prep — Communication, Light Signals & Runway Lighting Systems

Aircraft lighting systems serve distinct operational purposes and are categorized accordingly:

Position (Navigation) Lights

  • Red light on the left wingtip
  • Green light on the right wingtip
  • White light on the tail
  • Required for night operations under 14 CFR 91.205
  • Must meet specific color and intensity standards per 14 CFR 91.209

Anti-Collision Lights

  • Rotating beacon (typically red, located on the top and/or bottom of the fuselage)
  • Strobe lights (high-intensity flashing white lights, typically on wingtips and tail)
  • Required for both day and night operations under 14 CFR 91.209
  • Must be operational before flight; no MEL relief for Part 91 operations

Landing and Taxi Lights

  • Landing lights: Required for night operations per 14 CFR 91.205(b)(11)
  • Taxi lights: Used for ground maneuvering
  • High-intensity illumination for approach, landing, and taxi operations

Instrument Panel Lights

  • Illuminate cockpit instruments for night operations
  • Typically controlled by a dimming rheostat
  • Must not produce glare or reflections that impair pilot vision

2. Electrical Circuit Fundamentals for Lighting Systems

Understanding the electrical path from power source to light is essential for effective troubleshooting:

Power Distribution Path

Power Distribution Path — Source to Load with Fault Tracing Power Distribution Path — Source to Load FAA A&P ACS — Electrical System Fault Tracing Sequence POWER SOURCE Battery / Alternator BUS BAR Distribution point 14/28 VDC CIRCUIT BREAKER Overcurrent protection SWITCH SPST / Toggle WIRING & CONNECTORS AWG 22, crimp type LOAD Landing light Return path (ground) CLOSED 1. Source 2. Bus 3. Breaker 4. Switch 5. Load Fault Tracing Sequence (AC 43.13-1B): 1. Verify power at source → 2. Check bus voltage 3. Test breaker continuity → 4. Confirm switch operation 5. Inspect wiring/connectors → 6. Test load 28V 28V 28V 28V 5A Legend Current flow Switch / breaker action Return path
  1. Power source (battery/alternator/generator)
  2. Bus bar
  3. Circuit breaker (protection device)
  4. Switch (control device)
  5. Wiring (conductors)
  6. Connectors/terminals
  7. Load (light fixture/bulb)

Voltage Drop Principles

  • Every connection, switch contact, and length of wire introduces resistance
  • Excessive resistance reduces voltage available at the load
  • A dim light typically indicates high resistance in the circuit, not a complete failure
  • Voltage drop testing is the primary diagnostic method per AC 43.13-1B Chapter 11

Circuit Protection

  • Circuit breakers protect wiring from overcurrent conditions
  • A tripped breaker indicates an overcurrent event (short circuit or excessive current draw)
  • Never reset a tripped breaker without identifying and correcting the root cause
  • Repeated tripping indicates a persistent fault requiring systematic troubleshooting

3. Troubleshooting Methodology

Systematic troubleshooting follows a logical progression from simple to complex:

Initial Steps

  1. Verify power is reaching the component (check circuit breaker, switch position)
  2. Check voltage at the component terminals
  3. Test the component itself (continuity, resistance)
  4. Inspect wiring and connections for damage, corrosion, or chafing

Voltage Present, Light Not Working

  • If correct voltage is measured at the connector, the bulb or component is likely faulty
  • Test the bulb for continuity or replace with a known-good unit

No Voltage at Component

  • Trace the circuit backward toward the power source
  • Check circuit breaker (tripped?)
  • Check switch operation and contacts
  • Inspect wiring for opens, shorts, or chafing

Dim Light Symptoms

  • Indicates voltage drop due to high resistance
  • Check for corrosion at terminals and connectors
  • Verify ground circuit integrity
  • Measure voltage at the load and compare to source voltage
  • Inspect switch contacts for pitting or burning

Intermittent Operation

  • Often caused by loose connections or chafed wiring
  • Physical manipulation (wiggling) of wiring can help isolate the fault
  • Inspect connectors for proper seating and terminal tension

4. Regulatory Requirements

14 CFR 91.205 – Instrument and Equipment Requirements

  • Position lights required for night operations
  • Anti-collision light system required for both day and night operations (per 91.209)
  • Landing light required for night operations (for hire or commercial operations)

14 CFR 91.209 – Aircraft Lighting

  • No person may operate an aircraft during night unless position lights are lighted
  • Anti-collision lights must be lighted during all operations (day and night)
  • An inoperative anti-collision light must be repaired before flight; no deferral permitted under Part 91

14 CFR 43.9 – Maintenance Record Entries

  • Any maintenance performed must be recorded
  • Entry must include: description of work, date, mechanic's signature, and certificate number
  • Applies to minor repairs such as lens replacement

AC 43.13-1B – Acceptable Methods, Techniques, and Practices

  • Chapter 11 covers aircraft electrical systems
  • Provides guidance for wire repair, splicing, and protection
  • Emphasizes systematic troubleshooting and voltage drop testing
  • Requires following manufacturer's instructions for component installation and cooling

5. Wiring Maintenance Standards

Wire Repair Requirements

  • Chafed wiring is a fire and safety hazard requiring proper repair
  • Taping is a temporary fix, not an approved repair method
  • Approved repairs include proper splicing with soldered connections or approved connectors
  • Protect wires passing through bulkheads with grommets or clamps
  • Follow AC 43.13-1B Chapter 11 for acceptable methods

Connector and Terminal Maintenance

  • Secure loose connections and protect from corrosion
  • Inspect for signs of overheating (discoloration, melting)
  • Verify proper terminal tension and seating
  • Use approved anti-corrosion compounds where specified

6. Component-Specific Considerations

Strobe Light Power Supplies

  • Convert aircraft DC power to high-voltage pulses for strobe tubes
  • Require adequate ventilation to prevent overheating
  • Mount per manufacturer's instructions
  • Output voltage must be verified during functional testing
  • Faulty lamps or wiring can affect power supply output

Rotating Beacons

  • Electromechanical or solid-state flashing devices
  • Motor brushes may require replacement (component-level check after verifying power)
  • Verify power path: circuit breaker → switch → beacon

Rheostats (Instrument Panel Dimming)

  • Variable resistors controlling panel light intensity
  • Test with ohmmeter while rotating knob
  • Look for resistance jumps or open circuits indicating worn internal contacts
  • Test with power removed (non-energized)

Light Lenses

  • Must maintain proper color and intensity characteristics
  • Faded or discolored lenses can render lights non-compliant
  • Replace with approved parts (PMA or OEM)
  • Document replacement per 14 CFR 43.9

7. Airport Lighting Systems

Runway Edge Lights

  • Series circuits with constant current regulators
  • Tripped breakers indicate overcurrent conditions (short circuits, failed lamps)
  • Isolate and repair faults before resetting

Runway Centerline Lighting

  • Flickering often caused by loose or corroded connections
  • Inspect constant current regulator connections first
  • Tighten connections and verify proper contact

Taxiway Edge Lights

  • Same series circuit principles as runway lighting
  • Tripped breakers require fault isolation before reset

8. Post-Lightning Strike Inspection

After a lightning strike, the lighting system requires special attention:

  • Inspect all wiring for arcing, burning, and insulation breakdown
  • Check components for electrical damage
  • Look for latent failures that may not be immediately apparent
  • Verify all lighting systems function correctly before return to service

Important Procedures and Practices

Systematic Troubleshooting Sequence

Systematic Troubleshooting Sequence - Eight-Step Flow Systematic Troubleshooting Sequence — Eight-Step Flow STEP 1 Verify the Symptom STEP 2 Check the Obvious STEP 3 Verify Power at Component STEP 4 Test the Component PASS? (AC 43.13-1B) FAIL STEP 5 Inspect the Circuit STEP 6 Repair the Fault STEP 7 Functional Test STEP 8 Document the Work PASS → RETEST / VERIFY Operational check Visual inspection Use DMM per 43.13 Continuity / load 14 CFR Part 43 • AC 43.13-1B • FAA ACS — Systematic Troubleshooting LEGEND Pass / Normal Fail / Repair path
  1. Verify the symptom – Confirm the reported malfunction
  2. Check the obvious – Circuit breaker, switch position, bulb condition
  3. Verify power at the component – Measure voltage at the load terminals
  4. Test the component – Continuity check or replacement with known-good unit
  5. Inspect the circuit – Wiring, connectors, grounds, and switch contacts
  6. Repair the fault – Use approved methods and materials
  7. Functional test – Verify proper operation after repair
  8. Document the work – Make required logbook entries

Voltage Drop Testing Procedure

Voltage Drop Testing Procedure - FAA A&P Communication, Light Signals, and Runway Lighting Systems Voltage Drop Testing Procedure FAA A&P Prep — Communication, Light Signals & Runway Lighting Systems STEP 1: SOURCE VOLTAGE Battery V 12.6 Measure at battery terminals with circuit energized STEP 2: LOAD VOLTAGE Load (lamp) V 12.2 R Measure at load terminals with circuit energized STEP 3: CALCULATE DROP Drop = Source − Load 12.6V − 12.2V = 0.4V 3% limit 0.4V = 3.17% — EXCESSIVE AC 43.13-1B: max 3% for lighting circuits STEP 4: DIAGNOSIS — HIGH RESISTANCE CONNECTION Battery R Corroded connection Switch Lamp (dim) Voltage Drop Source: 12.6V At load: 12.2V Drop: 0.4V (3.17%) INSPECTION REQUIRED • Check terminal connections • Clean corrosion, tighten lugs • Verify per AC 43.13-1B Ch. 11 14 CFR Part 43 · AC 43.13-1B · FAA A&P Knowledge Exam Reference
  1. Measure source voltage (battery/bus)
  2. Measure voltage at the load with the circuit energized
  3. Calculate voltage drop (source voltage minus load voltage)
  4. Acceptable drop: typically less than 3% for lighting circuits (refer to manufacturer data)
  5. Excessive drop indicates high resistance – inspect connections, switches, and wiring

Circuit Breaker Handling

  • A tripped breaker indicates an overcurrent condition
  • Do NOT reset without identifying the cause
  • Inspect for short circuits, chafed wiring, and failed components
  • If the breaker trips again after reset, the fault persists – continue troubleshooting
  • Document all breaker trips and corrective actions

Functional Testing Requirements

  • Always perform a functional test after any repair or component replacement
  • Verify proper operation under actual operating conditions
  • Check all modes (e.g., steady, flashing, high/low intensity)
  • Confirm proper color and intensity for position lights

Common Relationships and Principles

Dim Light = High Resistance

Dim Light = High Resistance - Voltage Drop Testing Dim Light = High Resistance Voltage Drop Testing — Corrosion & Loose Connections BATTERY 12V DC + / − SWITCH CORROSION VOLTMETER 2.1V VOLTAGE DROP 2.1V across corrosion HIGH RESISTANCE CAUSES • Corrosion at connectors • Loose terminal connections • Worn switch contacts • Undersized wire (excess length) Result: Dim light, heat at fault, voltage measured at load is low. AC 43.13-1B Ch. 11 §7 VOLTAGE DROP TEST PROCEDURE 1. Place voltmeter leads across suspect connection (load energized). 2. Reading > 0.1V per connection indicates excessive resistance. 3. Max acceptable: 0.5V total for 12V system (AC 43.13-1B). 28V BULB (DIMMED) R = HIGH 2.5Ω !
  • Dim illumination indicates voltage drop, not a complete circuit failure
  • Corrosion, loose connections, and worn switch contacts are typical causes
  • Voltage drop testing identifies the location of excessive resistance

Tripped Breaker = Overcurrent

Tripped Breaker = Overcurrent — Find the Cause Before Resetting Tripped Breaker = Overcurrent Short Circuit / Excessive Current Draw — Root Cause Must Be Found Before Reset POWER SOURCE 28 VDC Bus +28V C/B 5 AMP TRIP SHORT CIRCUIT (Arc flash / fault current) LOAD Motor / Device Ground / Return Path RESET? ⚠ DO NOT RESET — FIND THE ROOT CAUSE FIRST! Identify and correct the short circuit or excessive load before resetting TROUBLESHOOTING CHECKLIST (AC 43.13-1B / 14 CFR 91.7): 1. Inspect wiring for chafing, damaged insulation, or loose connections 2. Verify load does not exceed breaker rating — check for stalled motor or shorted component 3. Use megger/ohmmeter to isolate fault — repair or replace defective component before reset ! OVERCURRENT TRIPPED
  • Indicates a short circuit or excessive current draw
  • Failed components can cause overcurrent conditions
  • Always find and correct the root cause before resetting

Intermittent Operation = Loose Connection

  • Movement-sensitive failures indicate poor electrical contact
  • Wiggling wiring harnesses can help isolate the fault location
  • Inspect connectors, terminals, and chafing points

No Voltage at Component = Open Circuit

  • Trace the power path backward from the load
  • Check breaker, switch, and wiring continuity
  • A tripped breaker is a common cause of complete voltage loss

Correct Voltage Present = Component Failure

  • If proper voltage is measured at the load terminals, the component itself is faulty
  • Test the bulb or unit for continuity
  • Replace with an approved part

Required Equipment = Must Be Operational

  • Position lights, anti-collision lights, and landing lights (when required) must function
  • No deferral is permitted under Part 91 for these items
  • Inoperative required equipment grounds the aircraft until repaired

Summary of Key Regulations and References

ReferenceApplication
14 CFR 91.205Equipment requirements for night operations
14 CFR 91.209Aircraft lighting requirements
14 CFR 43.9Maintenance record entries
AC 43.13-1B Chapter 11Acceptable electrical system maintenance practices
FAA AMT Handbook, General, Chapter 7Electrical system fundamentals and troubleshooting

Conclusion

Aircraft lighting systems are safety-critical components that require systematic troubleshooting and proper maintenance. Understanding the electrical principles governing these systems, the regulatory requirements for their operation, and the approved maintenance practices is essential for the AME. The key to effective troubleshooting lies in following a logical progression from verifying power at the component to testing the component itself, while always considering the most likely causes first. Proper documentation and adherence to approved methods ensure both airworthiness and regulatory compliance.

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