FAA Airframe Written TestChapter 3 · 40 practice questions

Chapter 3: Flight Controls

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Chapter: Flight Controls

Overview

This chapter covers the inspection, maintenance, rigging, and troubleshooting of aircraft flight control systems. It addresses the critical safety requirements for primary and secondary flight controls, including ailerons, elevators, rudders, and trim systems. The material emphasizes the regulatory framework governing flight control maintenance, the identification of defects, proper repair procedures, and the systematic approach to diagnosing control system discrepancies.

Key Concepts

1. Control Cable Inspection and Replacement Criteria

Control cables are the backbone of mechanical flight control systems. Their integrity is critical to safe operation, and specific inspection criteria determine airworthiness.

Broken Wire Criteria

Control Cable Inspection Criteria - AC 43.13-1B CONTROL CABLE INSPECTION CRITERIA — AC 43.13-1B CABLE CROSS-SECTION 7×19 Aircraft Cable — 1/8" dia. ⚠ 2 ADJACENT BROKEN = REJECT ⚠ 6+ PER INCH = REJECT MAX 6 BROKEN WIRES/INCH (NOT ADJACENT) INSPECTION ZONES RUN 6 wires/inch limit PULLEY 2 wires/ layer TERMINAL 0 broken wires CORROSION PITTING LIMITS: No pits deeper than 1/3 wire dia. No chain pitting along length DECISION FLOW START INSPECTION VISUAL — BROKEN WIRES? 6+/IN? YES REJECT NO CORROSION PITTING? SERVICEABLE WEAR / FLATTENED SPOT CRITERIA FLAT SPOT • Flattened spots: reject if wear exceeds 1/3 of wire diameter • Measure with micrometer at narrowest point of flattened area • Check for bird-caging, kinks, heat damage, or fraying WEAR DEPTH GAUGE REF: AC 43.13-1B CH. 7, SEC. 3 14 CFR §43.12 INSPECTION ZONE DETAILS — WHERE TO LOOK RUN ZONE • Straight cable segments between pulleys • Max 6 broken wires per inch • No 2 adjacent broken wires • Check for uniform tension • Look for wear patterns PULLEY ZONE • 2x cable diameter each side of pulley • Max 2 broken wires per layer • Check pulley groove wear • Verify cable seating in groove • Check for side wear TERMINAL END • Swaged fittings — no broken wires • Check for cracks at fitting • Verify swage dimensions • Check for corrosion at ends • Confirm no wire protrusion

Per AC 43.13-1B, control cables must be replaced when any of the following conditions exist:

  • Any broken wires within the vicinity of a terminal, fitting, or swage — regardless of the number, this condition is immediately unairworthy
  • More than 3 broken wires in any 12-inch length of cable run
  • Frayed strands anywhere along the cable length
  • Corrosion with pitting — corrosion reduces the cable's cross-sectional area and creates stress risers that can lead to catastrophic failure

Critical Considerations

  • Splicing is never an approved repair for primary flight control cables
  • Soldering is prohibited because it creates stress risers and can mask internal damage
  • Cleaning and applying corrosion inhibitor is not acceptable for cables with pitting — the cable must be replaced
  • Broken wires near pulleys or fairleads indicate possible routing problems, chafing, or pulley damage that must also be investigated

Inspection Focus Areas

Pay particular attention to:

  • Points where cables pass over pulleys
  • Areas near turnbuckles and terminals
  • Sections passing through fairleads
  • Any location where the cable changes direction

2. Cable Tension and Rigging

FAA A&P Flight Controls - Cable Tension and Rigging Cable Tension and Rigging — Flight Controls AC 43.13-1B / 14 CFR ANCHOR BELLCRANK TURNBUCKLE TENSIOMETER LOW TENSION → SLACK / FLUTTER RISK CORRECT TENSION → SMOOTH OPERATION HIGH TENSION → WEAR / PULLEY STRESS LOW TENSION • Cable slack & play • Control surface flutter • Incorrect rigging CORRECT TENSION • Per rigging chart spec • Set at chart temperature • Smooth control response HIGH TENSION • Accelerated cable wear • Pulley bearing stress • Possible cable failure RIGGING CHART — TENSION VS TEMPERATURE -40°F -20°F 0°F 20°F 40°F 60°F 80°F ▲ SET TENSION AT CURRENT AMBIENT TEMP — REFER TO CHART ADJUST Procedure: 1. Check rigging chart → 2. Apply tensiometer → 3. Adjust turnbuckle → 4. Safety wire

Proper cable tension is essential for correct flight control operation. Both excessive and insufficient tension create distinct problems.

Low Cable Tension Effects

  • Spongy or mushy control feel — the pilot perceives a soft, non-positive response
  • Excessive free play in the control wheel or pedals before surface movement
  • Control surface flutter — the most dangerous consequence; flutter is a violent, destructive oscillation that can cause structural failure
  • Inconsistent control response during maneuvering

High Cable Tension Effects

  • Stiff or heavy control forces — the pilot must exert excessive effort to move the controls
  • Restricted control surface travel — the surface may not reach its full deflection limits
  • Premature wear on pulleys, fairleads, and cable attachments
  • Binding in the control system

Tension Adjustment Procedure

  1. Position all flight controls in the neutral position
  2. Reference the manufacturer's maintenance manual for the specified tension range
  3. Adjust tension using turnbuckles
  4. Account for ambient temperature — cable tension specifications are temperature-compensated
  5. Safety all turnbuckles after adjustment
  6. Verify full range of motion of all control surfaces
  7. Confirm cockpit controls are correctly positioned

Turnbuckle Safety

Turnbuckle Safety Wiring Procedure - FAA A&P Prep Turnbuckle Safety Wiring — FAA A&P Procedure (AC 43.13-1B) Cable Eye Barrel Cable Eye Safety Wire Holes 1 Adjust Tension First Set cable tension to spec BEFORE installing safety wire 2 Route Wire Through Barrel Holes Pass wire through both holes, leave slack for wrapping 3 Wrap Both Ends (4-6 turns) Wrap wire around each end of barrel, pulling tight 4 Clip & Bend Ends Cut excess wire, bend ends back to prevent snagging 5 Final Inspection Verify wire is tight, no gaps, turns are uniform (AC 43.13-1B) ⚠ Never safety wire before final adjustment Correct Wrap Pattern 4-6 turns minimum Wire ends bent back ⚠ Adjust tension BEFORE safetying AC 43.13-1B Chapter 7, Section 7-10 ⚠ Adjust tension BEFORE safetying 14 CFR §43.13-1B — Acceptable methods, techniques, and practices
  • Turnbuckles must be properly safetied after any tension adjustment
  • Loose turnbuckles are a common cause of spongy controls and excessive free play
  • Safety wire must be installed correctly to prevent turnbuckle rotation

3. Control System Free Play

Free play is the movement of a cockpit control before the corresponding control surface begins to move. Excessive free play is a serious safety issue.

Causes of Excessive Free Play

Control System Free Play Troubleshooting Flow Control System Free Play Troubleshooting — Symptom-Based Decision Flow EXCESSIVE CONTROL FREE PLAY STEP 1 — INSPECT BELLCRANK BEARINGS Check for radial play, flat spots, corrosion, or brinelling (AC 43.13-1B) BEARINGS WORN? YES REPLACE BEARINGS Per manufacturer SB / IPC NO STEP 2 — CHECK BOLT HOLES FOR ELONGATION Measure hole diameter vs. bolt; look for ovalization, fretting, or cracks (14 CFR 43) STEP 3 — INSPECT HINGES & BUSHINGS Check hinge pin wear, bushing ID, and surface fretting per AC 43.13-1B Ch.4 CABLE STRETCH? CHECK RIGGING Tension per AMM COMMON CAUSES Worn bearings Elongated holes Hinge wear Cable stretch Loose attach Bushing wear AC 43.13-1B Chapter 4 · 14 CFR Part 43 · FAA A&P Airframe Oral & Practical
  • Incorrect cable tension — either too loose or improperly adjusted
  • Worn cable system components — pulleys, fairleads, and attachment points
  • Worn bellcrank bearings or bushings
  • Elongated bolt holes in control system components
  • Worn hinge points on control surfaces
  • Loose turnbuckles

Troubleshooting Approach

When excessive free play is detected:

  1. Check cable tension first — this isolates cable stretch/slack from worn components
  2. Inspect the entire system — cables, pulleys, bellcranks, and attachment points
  3. Identify the specific source of play before making adjustments
  4. Correct the root cause — do not mask the problem with temporary fixes

Consequences of Uncorrected Free Play

  • Control surface flutter
  • Reduced control authority
  • Autopilot hunting or oscillation (the autopilot servos command movement, but slack in the system causes delayed feedback and overshooting)
  • Pilot perception of sloppy or imprecise aircraft handling

4. Control System Rigging

Rigging is the process of adjusting the control system so that cockpit controls and control surfaces are properly synchronized.

Neutral Position Alignment

Control System Rigging — Neutral Position CONTROL SYSTEM RIGGING — NEUTRAL POSITION STEP 1: ALIGN TO NEUTRAL Set control surfaces per maintenance manual neutral position (rig pins installed) AC 43.13-1B Ch. 2 §2-5 STEP 2: CHECK TRAVEL Verify full deflection in both directions against rigging limits (degree marks) 14 CFR §23.677 / §25.677 STEP 3: VERIFY DIRECTION Control surface movement must match cockpit input direction (e.g., yoke left → aileron up) ACS P.A.II.C.K1 STEP 4: POST-RIGGING FUNCTIONAL TEST Cycle controls through full travel — verify smooth operation, no binding, correct cable tension, and proper return to neutral when released. Document results per maintenance manual. AIRCRAFT REFERENCE LINE -25° +25° NEUTRAL 0° 10° -10° 20° -20° CONTROL SURFACE COCKPIT INPUT DIRECTION MATCH ✓ VERIFIED RIG PIN INSTALLED ▼ LIMIT ▼ LIMIT CABLE TENSION CABLE TENSION 1 2 3 4
  • With cockpit controls in neutral, control surfaces must be in their neutral position
  • A rudder deflected with pedals neutral indicates improper cable tension or adjustment
  • An aileron that moves before the control wheel moves indicates free play

Travel Limits

  • Control stops must be adjusted to ensure symmetrical travel
  • Example: If the rudder travels +25° right but only -22° left, the control stops are incorrectly adjusted
  • Asymmetric control wheel travel in one direction versus the other is typically caused by improperly adjusted control stops
  • Control stops prevent overtravel and must be set precisely per the maintenance manual

Direction of Movement

  • Control surfaces must move in the correct direction relative to cockpit control input
  • Reversed controls occur when cables are crossed at a bellcrank or quadrant
  • A reversed control is a critical flight safety hazard
  • A functional test is required after any rigging work to verify correct direction of movement

Post-Rigging Functional Test

After any rigging procedure:

  1. Move cockpit controls through their full range
  2. Verify control surfaces move in the correct direction
  3. Confirm full travel in both directions
  4. Check that neutral positions align
  5. Verify control forces are within acceptable limits

5. Control Surface Inspection and Damage Assessment

Structural Damage Assessment

Control Surface Damage Assessment Flow - FAA A&P Prep Control Surface Damage Assessment Flow — FAA A&P Prep DAMAGE FOUND 1. IDENTIFY TYPE Dent / Crack / Corrosion Loose Skin / Delamination 2. MEASURE Depth, Length, Width Use calibrated tools WITHIN ADL? (Allowable Damage Limits) YES NO WITHIN ADL Continue in service per AC 43.13-1B Ch.4 EXCEEDS ADL Repair per SRM/MM or Replace component REPAIRABLE? (Per SRM limits) DOCUMENT PER: 14 CFR §43.9 — Sign-off AC 43.13-1B — Methods ✓ DAMAGE CRITERIA • Dents: <0.1" deep ok • Cracks: stop-drill & re-evaluate per SRM • Corrosion: pitting >10% thickness = replace • Loose skin: tap test for delamination ADL REFERENCE • AC 43.13-1B Ch.4 Table 4-1 • SRM 51-00-XX (per aircraft) • Manufacturer structural manual Inspect FLOW: IDENTIFY → MEASURE → COMPARE → REPAIR/REPLACE → DOCUMENT

When damage is found on a control surface:

  1. Determine if the damage is within the manufacturer's allowable damage limits — this is always the first step
  2. If within limits, the aircraft may be returned to service, but the finding should be recorded in the logbook for traceability
  3. If beyond limits, repair or replacement is required
  4. If no repair procedure exists in the maintenance manual, obtain an approved repair method from the manufacturer

Damage Categories

  • Cracks — any crack in a flight control surface is a structural defect requiring repair before return to service
  • Dents — may be cosmetic or structural; assess against allowable damage limits
  • Corrosion — reduces structural integrity and must be evaluated
  • Fabric damage — even if the fabric is intact, a dent may affect structural integrity or control surface balance

Repair Documentation

  • Damage within allowable limits must be recorded in the logbook
  • Repairs must use approved methods (manufacturer's structural repair manual or AC 43.13-1B Chapter 2)
  • Ad-hoc repairs are never acceptable
  • Replacement is only necessary if the manufacturer determines damage is beyond repair

6. Component Wear and Defects

Bellcranks

  • A cracked bellcrank in a flight control system is a major defect
  • Without an approved repair procedure, the only safe and legal action is replacement
  • Welding a cracked bellcrank without an approved procedure is prohibited

Hinges and Bushings

  • Worn hinge bushings cause excessive play at the control surface
  • Replacement of worn bushings is the appropriate repair to restore designed tolerance
  • Tightening bolts or adding washers is not an approved repair for hinge wear
  • Excessive play at a hinge must be corrected before return to service

Balance Weights

  • A loose balance weight must be tightened to the manufacturer's torque specification
  • Removal of balance weights renders the aircraft unairworthy
  • Proper securing methods include cotter pins or other approved locking devices

Trim Tab Actuators

  • Excessive wear in a trim tab actuator that fails to hold position requires replacement
  • Installing used or repaired parts without proper documentation is not acceptable
  • Safety wiring a defective tab in neutral is not an approved temporary repair

Cotter Pins and Castle Nuts

  • A missing cotter pin in a flight control system is a serious safety issue
  • Replace the castle nut with a new one, torque to specification, and install a new cotter pin
  • Never reuse cotter pins
  • Thread-locking compound is not a substitute for mechanical locking in flight control systems

7. Troubleshooting Control System Problems

Symptom-Based Diagnosis

SymptomLikely CauseInvestigation Priority
Spongy controlsLow cable tension or air in hydraulic boost systemCheck cable tension; check hydraulic system for air
Stiff/heavy controlsExcessive cable tension or bindingCheck cable tension; perform free play check
Excessive free playLow cable tension or worn componentsCheck cable tension first, then inspect components
Control surface not respondingBroken or disconnected cableInspect control path continuity
Reversed control movementCrossed cables at bellcrank/quadrantVerify cable routing
Asymmetric travelIncorrectly adjusted control stopsAdjust control stops
Trim tab buzzingWorn hingeReplace hinge
Autopilot huntingExcessive free play in control systemCheck rigging and cable tension

Systematic Troubleshooting Approach

  1. Gather information — pilot reports, inspection findings, maintenance history
  2. Perform initial checks — cable tension, free play, visual inspection
  3. Isolate the system — determine if the problem is in the cockpit controls, cable system, or control surface
  4. Identify root cause — do not treat symptoms without finding the underlying issue
  5. Correct the defect — use approved methods and parts
  6. Verify the repair — functional test the system

8. Regulatory Requirements

14 CFR 43.13(a) — Performance Standards

  • Maintenance must be performed using methods that ensure the aircraft is in a condition for safe operation
  • All repairs must use methods and parts acceptable to the FAA

14 CFR 43.15 — 100-Hour Inspection Requirements

  • All discrepancies found during a 100-hour inspection must be corrected before the aircraft is returned to service
  • This includes flight control system defects

14 CFR 43.9 — Maintenance Record Entries

Required elements of a maintenance record entry:

  • Description of the work performed
  • Date of completion
  • Signature and certificate number of the person approving the aircraft for return to service

14 CFR 91.7 — Civil Aircraft Airworthiness

  • No person may operate a civil aircraft unless it is in an airworthy condition
  • The pilot-in-command is responsible for determining airworthiness

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

  • Provides acceptable methods for aircraft inspection and repair
  • Chapter 2 covers aircraft structures
  • Chapter 5 covers flight controls
  • Chapter 7 covers cable operations and systems

Important Procedures

Control Cable Replacement Procedure

  1. Remove the old cable, noting the routing path
  2. Inspect all pulleys, fairleads, and attachment points for wear or damage
  3. Install the new cable following the exact routing path
  4. Rig the system to the manufacturer's specifications
  5. Adjust cable tension to the specified range for ambient temperature
  6. Safety all turnbuckles
  7. Verify full range of motion of control surfaces
  8. Confirm cockpit controls are correctly positioned
  9. Perform a functional test to verify correct direction of movement
  10. Document the work in the maintenance record

Control System Free Play Check

  1. Position the cockpit control in neutral
  2. Apply light pressure in one direction
  3. Measure the movement of the cockpit control before the control surface begins to move
  4. Repeat in the opposite direction
  5. Compare measurements to manufacturer's specifications
  6. If excessive, check cable tension first, then inspect system components

Damage Assessment Procedure

  1. Document the damage (location, size, type)
  2. Consult the manufacturer's maintenance manual for allowable damage limits
  3. If within limits — record the finding and return to service
  4. If beyond limits — determine if a repair procedure exists
  5. If a repair procedure exists — perform the repair using approved methods
  6. If no repair procedure exists — obtain manufacturer approval for a repair method or replace the component

Common Relationships Between Concepts

Cable Tension and Control Feel

  • Low tension → spongy feel, free play, potential flutter
  • High tension → stiff feel, restricted travel, premature wear
  • Correct tension → positive, responsive control feel

Free Play and System Wear

  • Free play is often the first indicator of system wear
  • Cable tension should be verified before condemning components
  • Worn components (bearings, bushings, bellcranks) contribute to free play even with correct cable tension

Rigging and Control Travel

  • Correct rigging ensures symmetrical travel in both directions
  • Control stops determine maximum travel limits
  • Cable tension affects both control feel and travel

Hydraulic Systems and Control Feel

  • Air in hydraulic boost systems causes spongy feel
  • Hydraulic leaks require repair and functional testing
  • Hydraulic restrictions cause sluggish response or hardover conditions

Autopilot Interaction with Mechanical Systems

  • Autopilot hunting often indicates mechanical free play
  • The autopilot system itself may be functioning correctly
  • Always verify mechanical control system rigging before condemning autopilot components

Documentation and Airworthiness

  • All maintenance must be properly documented
  • Damage within limits must be recorded for traceability
  • Return to service requires compliance with 14 CFR 43.9
  • Proper documentation ensures the chain of airworthiness is maintained

Summary

Flight control maintenance requires a systematic approach that combines thorough inspection, accurate diagnosis, and proper repair procedures. The key principles are:

  1. Control cables must be replaced when any broken wires, fraying, or corrosion pitting is found
  2. Cable tension must be within manufacturer's specifications — both excessive and insufficient tension create safety hazards
  3. Free play must be investigated systematically — check cable tension first, then inspect components
  4. Rigging must ensure correct direction, neutral alignment, and symmetrical travel
  5. Structural damage must be assessed against allowable limits before any repair decision
  6. All discrepancies must be corrected before return to service
  7. Proper documentation is mandatory for all maintenance actions

Adherence to these principles ensures flight control systems operate safely and reliably, meeting both regulatory requirements and the highest standards of aviation safety.

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