FAA Airframe Written TestChapter 4 · 40 practice questions

Chapter 4: Airframe Inspection

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Airframe Inspection

Overview

This chapter covers the systematic process of inspecting aircraft airframes to ensure they meet airworthiness standards. It integrates regulatory requirements, manufacturer specifications, and accepted maintenance practices. The material addresses how to identify, evaluate, and document discrepancies found during inspections, emphasizing the legal responsibilities of the mechanic and the safety-critical nature of the work. Key areas include compliance with Airworthiness Directives (ADs), evaluation of structural damage and corrosion, assessment of flight control systems, and proper documentation per federal regulations.

AD Compliance Decision Flow - Airframe Inspection AD Compliance Decision Flow — Airframe Inspection 14 CFR 91.403 · AC 43.13-1B · FAA A&P ACS INSPECTION CHECKLIST □ Fuselage □ Wings □ Empennage □ Powerplant ■ AD Compliance AD COMPLIANCE CHECK AD #2024-15-03 Due: 01/15/2025 OVERDUE 14 CFR 91.403(a) Legally enforceable UNAIRWORTHY ⚠ Immediate grounding per 14 CFR 91.403 MECHANIC ACTION 1. Inform owner of AD status 2. Do NOT return to service 3. Route to owner for compliance 🔧 OWNER ACTION Schedule compliance per AD requirements RETURN TO SERVICE √ Airworthy REPETITIVE AD NOTICE Repetitive ADs lapse the same way if the interval is missed — track next due date in the aircraft maintenance log. AD check overdue notify comply release Inspection flow Unairworthy Compliant

Key Concepts

1. Airworthiness Directives (ADs) and Regulatory Compliance

An Airworthiness Directive (AD) is a legally enforceable rule issued by the FAA that applies to a specific aircraft, engine, or component. Compliance with all applicable ADs is a prerequisite for an aircraft to be considered airworthy.

  • Overdue ADs: If an inspection reveals that an AD has not been complied with, the aircraft is immediately unairworthy. The mechanic must inform the owner and ensure the AD is complied with before returning the aircraft to service. Returning an aircraft to service with an overdue AD is a direct violation of 14 CFR 91.403, which states that no person may operate an aircraft to which an AD applies unless it has been complied with.
  • Repetitive ADs: Some ADs require repetitive inspections or actions at specified intervals. If the interval has lapsed, the aircraft is non-airworthy until the required action is performed. The mechanic can perform the AD inspection and document it, but the aircraft cannot be flown until compliance is achieved. This is per 14 CFR 39.7 and 14 CFR 91.403.
  • Authorization: A mechanic cannot perform an AD without authorization from the owner or operator. The mechanic's role is to inform the owner of the discrepancy and the required corrective action.

2. Inspection Types and Grace Periods

Annual vs 100-Hour Inspection Timelines — 14 CFR 91.409 ANNUAL vs 100-HOUR INSPECTION TIMELINES — 14 CFR 91.409 ANNUAL INSPECTION (ALL PART 91 AIRCRAFT) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec DUE LAST 12 calendar months (not 12 months from date of manufacture) 100-HOUR INSPECTION (CARRIES PERSONS FOR HIRE / FLIGHT INSTRUCTION) 0 hrs 50 hrs 90 hrs 100 hrs hrs 10-HOUR GRACE PERIOD — OVERFLIGHT CONSEQUENCES GRACE OVERFLIGHT → ILLEGAL • May exceed 100 hrs by up to 10 hrs ONLY to reach a repair station (14 CFR 91.409(b)) • 100-hr inspection must be recorded in maintenance records — no grace for annual inspection Compliant Inspection window Grace period Overflight / violation AC 43.13-1B / 14 CFR 91.409 AIRWORTHY FAA A&P Prep — Airframe Inspection · SkyLicense · 14 CFR 91.409(a)(b) · AC 43.13-1B

14 CFR 91.409 outlines the requirements for annual and 100-hour inspections.

  • Annual Inspection: Required for all aircraft under Part 91. It is a comprehensive condition inspection that must be performed within every 12 calendar months.
  • 100-Hour Inspection: Required for aircraft that carry persons for hire or are used for flight instruction for compensation. This inspection is due every 100 hours of flight time.
  • 10-Hour Grace Period: If a 100-hour inspection is due, the aircraft may be flown for up to 10 hours to position it at a base where the inspection can be performed. This grace period is only for positioning the aircraft and does not apply to annual inspections. The aircraft must be safe for the flight, and a special flight permit is not required for this situation.
  • Missing Inspections: If a required inspection is missing from the logbook, the mechanic must perform the inspection and document it, noting that the previous inspection was omitted. Falsifying records or ignoring the issue is a violation of 14 CFR 43.9.

3. Structural Inspection and Damage Evaluation

The airframe structure must be inspected for cracks, corrosion, and damage. The Structural Repair Manual (SRM) or the manufacturer's maintenance manual provides allowable limits for damage.

  • Cracks: A crack that exceeds the allowable limit in the SRM makes the aircraft unairworthy. If the crack is within limits, it is not an immediate airworthiness concern, but it must be documented and repaired using approved data. Stop-drilling is a temporary measure and is not an acceptable final repair unless specifically approved by the manufacturer. For cracks in primary structural components (e.g., wing spar, engine mount, landing gear trunnion), replacement or repair per approved data is mandatory.
  • Corrosion: Corrosion within SRM limits is acceptable but must be treated and documented to prevent further corrosion. The standard practice is to remove the corrosion by blending, followed by the application of a corrosion-inhibiting compound. This is per AC 43.13-1B. Corrosion that exceeds limits requires replacement or an approved repair.
  • Non-Structural Fairings: Cracks in non-structural fairings (e.g., fiberglass) can be repaired using standard fiberglass repair techniques per AC 43.13-1B. These do not require replacement or grounding, but the repair must restore aerodynamic smoothness and be documented.
  • Approved Data: When a manufacturer's manual does not provide a repair procedure, the mechanic must use FAA-approved data. This includes the manufacturer's SRM, AC 43.13-1B, or an FAA Form 337 field approval. Repairs performed without approved data violate 14 CFR 43.13(a).

4. Control Cables and Flight Control Systems

Control cables are critical to flight safety and must be inspected for broken wires, corrosion, and wear.

  • Primary Flight Control Cables: Per AC 43.13-1B, any broken wire in a primary flight control cable is cause for replacement. The safety margin is critical, and even a single broken wire can indicate fatigue or damage. Splicing is not permitted for primary flight control cables.
  • Secondary Control Cables: For non-primary cables, the manufacturer's manual or AC 43.13-1B specifies allowable limits. For example, a cable may be allowed to remain in service if no more than 15% of the wires are broken in any one inch. However, any corrosion in a control cable is cause for replacement.
  • Rigging: Excessive free play in control surfaces (e.g., elevator trim tab) is a rigging discrepancy that must be corrected. The rigging should be adjusted to the middle of the specified tolerance to ensure proper operation without binding or excessive play. This follows the manufacturer's instructions and AC 43.13-1B.

5. Landing Gear and Hydraulic Systems

Landing gear components are safety-of-flight items that require careful inspection.

  • Down-Lock Springs: A cracked down-lock spring could allow the gear to collapse on landing. This is a safety-of-flight item that must be corrected before return to service.
  • Hydraulic Leaks: Hydraulic leaks must be repaired to ensure proper actuator operation. The first step in troubleshooting is to isolate the leak source, then determine if it is a minor seepage or a major leak requiring repair. Adding fluid without fixing the leak is unsafe and not acceptable.
  • Torque Link Bolts: A loose bolt with a missing cotter pin indicates possible wear or damage to the bolt threads. Per AC 43.13-1B, bolts with damaged threads or that show signs of looseness should be replaced, not reused. The correct action is to install a new bolt, torque to the manufacturer's specification, and secure with a new cotter pin.
  • Post-Hard-Landing Inspection: The first step is a thorough visual inspection to identify obvious damage, deformation, or leaks. This initial assessment guides further inspection or testing.

6. Tires, Brakes, and Fuel Systems

  • Tires: Tires worn to the fabric are unairworthy and must be replaced. This is a safety-critical condition that can lead to tire failure. Rotating tires does not address the worn condition.
  • Fuel Leaks: A fuel leak is a serious safety hazard. The correct action is to identify the source, repair it using approved methods (e.g., replacing damaged parts or re-torquing), and then perform a functional check to ensure the leak is resolved. Simply tightening might not address the root cause.
  • Fuel Strainers: Contamination (dirt and water) in a fuel strainer must be cleaned. This is a preventive maintenance task that must be documented per 14 CFR 43.9.

7. Safety Wiring and Fasteners

Safety wire is a secondary locking method for critical fasteners.

  • Missing or Broken Safety Wire: A missing or broken safety wire is a discrepancy that must be corrected. The bolt may be torqued, but the safety wire must be intact. Replacing the safety wire is a simple and proper corrective action per AC 43.13-1B.
  • Thread-Locking Compound: Thread-locking compound is not an acceptable substitute for safety wire on critical fasteners.
  • Loose Rivets: Replacing a loose rivet with the same size and type is a standard minor repair per AC 43.13-1B. Using a larger rivet, a bolt, or sealant are not approved methods and could compromise structural integrity.

8. Special Inspection Considerations

  • Aircraft in Storage: Aircraft in storage are prone to corrosion, animal nesting, and deterioration of rubber components. The inspector must consider these conditions during the inspection to ensure airworthiness. AC 43.13-1B provides guidance on inspecting stored aircraft.
  • Engine Chip Detectors: Metallic particles on a chip detector indicate internal engine wear or damage. The correct action is to stop the inspection, investigate the source of the metal (e.g., borescope, oil analysis), and follow manufacturer guidance. Running the engine or simply cleaning the detector could mask a critical failure.
  • Emergency Locator Transmitter (ELT): Per 14 CFR 91.207, the ELT must be inspected within 12 months after installation, and the battery must be replaced or recharged if it has been used or reached its expiration date. The mechanic must replace the battery, test the ELT (e.g., self-test) to ensure it operates, and make a logbook entry per 14 CFR 43.9.
  • Static Wicks: Static wicks are part of the aircraft's static discharge system, required for safe operation, especially in IFR conditions. Missing wicks are a discrepancy that must be corrected and documented.
  • Pitot-Static System: Per 14 CFR 91.411, the pitot-static system must be tested and inspected within the preceding 24 months for IFR operations. If a static port was obstructed, a leak test is necessary to ensure the system is functioning correctly.

Important Regulations and Procedures

RegulationDescription
14 CFR 39.7No person may operate an aircraft to which an AD applies unless it has been complied with.
14 CFR 43.2Maintenance and alterations must be performed using approved methods and data.
14 CFR 43.9Maintenance record entries must be made after maintenance, preventive maintenance, or alterations.
14 CFR 43.11Content, form, and disposition of records for inspections.
14 CFR 43.13(a)The mechanic must ensure that the aircraft is in a condition for safe operation.
14 CFR 43.15Annual and 100-hour inspections must determine the aircraft's condition.
14 CFR 91.7No person may operate a civil aircraft unless it is in an airworthy condition.
14 CFR 91.207ELT inspection and battery replacement requirements.
14 CFR 91.403No person may operate an aircraft to which an AD applies unless it has been complied with.
14 CFR 91.409Annual and 100-hour inspection requirements, including the 10-hour grace period.
14 CFR 91.411Pitot-static system test and inspection requirements for IFR operations.
AC 43.13-1BAcceptable methods, techniques, and practices for aircraft inspection and repair.

Common Relationships Between Concepts

  • Airworthiness = Compliance + Condition: An aircraft is airworthy only if it complies with all applicable ADs and regulations AND is in a condition for safe operation. A discrepancy in either area grounds the aircraft.
Airworthiness = Compliance + Condition - Two-Gate Concept Airframe Inspection — Airworthiness = Compliance + Condition 14 CFR §91.7 · AC 43.13-1B · FAA ACS AIRWORTHINESS = COMPLIANCE + CONDITION GATE 1: REGULATORY COMPLIANCE ✓ ADs current ✓ 14 CFR §91.7 ✓ AC 43.13-1B ✓ Logbook entries ✓ 100-hr / Annual ✓ Altitude equipment ✓ ELT / Transponder ✓ GATE 2: PHYSICAL CONDITION ✓ No cracks / corrosion ✓ Control travel OK ✓ Tires & brakes ✓ Fluid levels ✓ Wiring condition ✓ No leaks ✓ Structural integrity ✓ GROUNDED GROUNDED KEY CONCEPT Aircraft is airworthy ONLY if it passes BOTH gates. Failure of either gate → aircraft is grounded until discrepancy is corrected. ⚠ Any unresolved AD or unsafe condition = NOT airworthy
  • Inspection = Discovery + Correction: The purpose of an inspection is not just to find discrepancies but to correct them before return to service. All discrepancies found must be resolved, and the resolution must be documented.
Inspection = Discovery + Correction — FAA A&P Airframe Inspection Flow INSPECTION = DISCOVERY + CORRECTION 14 CFR §43.12 — Return to service requires all discrepancies resolved and documented 1. DISCOVER Find discrepancy (visual, operational, or scheduled check) ! 2. ASSIGN Route to correct maintenance action (AC 43.13-1B) 3. CORRECT Repair / replace / adjust per approved data / mfg manual 🔧 4. VERIFY Confirm fix works, no further damage, within limits ✓ RETURN TO SERVICE (14 CFR §43.12) ⚠ UNRESOLVED ✕ 5. LOG ENTRY — Documentation Required • Description of work performed (or reference to accepted data) • Date of completion • Name & certificate number of person approving • Signature & certificate type (IA for annual/100hr) • Airworthiness release statement per 14 CFR §43.9 feedback loop — inspection records drive future inspections KEY PRINCIPLE — 14 CFR §43.12: No person may approve an aircraft for return to service unless all discrepancies are resolved AND the maintenance record entry is completed. An inspection that finds a problem but does not fix it is NOT complete — discovery without correction is only a report. UNRESOLVED ITEMS BLOCK RETURN: ✕ Corrosion beyond limits — not treated ✕ Control cable tension out of tolerance ✕ Landing gear strut fluid leak RESOLVED & DOCUMENTED: ✓ Cracked cowl fastener — replaced per IPC ✓ Flap actuator — rigged & verified ✓ Static port blockage — cleared & tested FAA A&P Airframe Inspection — Discovery and Correction Flow Diagram
  • Approved Data = Legal Repair: Any repair, whether minor or major, must be based on approved data. This includes the manufacturer's SRM, AC 43.13-1B, or an FAA Form 337 field approval. Repairs without approved data are illegal and compromise safety.
Approved Data = Legal Repair — FAA A&P Airframe Inspection Approved Data = Legal Repair — Airframe Inspection 14 CFR §43.2 · AC 43.13-1B · FAA Form 337 · Manufacturer's SRM Repair Request Damage assessment completed per SRM APPROVED DATA GATE 14 CFR §43.2 — No repair without approved data ✓ DATA MATCH MANUFACTURER'S SRM Structural Repair Manual Specific aircraft data Approved by FAA / ODA AC 43.13-1B Acceptable Methods, Techniques & Practices Advisory Circular FAA FORM 337 Major Repair / Alteration Field Approval FAA Form 337 / 8100-9 ✓ LEGAL REPAIR Return to service per 14 CFR §43.5 ✗ ILLEGAL REPAIR No approved data Enforcement action 14 CFR §43.2 violation VIOLATION KEY REGULATORY REFERENCES • 14 CFR §43.2 — Records of inspection and maintenance • 14 CFR §43.5 — Approval for return to service after maintenance • AC 43.13-1B — Acceptable Methods, Techniques, and Practices • FAA Form 337 — Major Repair & Alteration record (airframe log entry) • Manufacturer's SRM — FAA-approved data specific to aircraft model repair data required match match match approved no match rejected Approved Data = Legal Repair — FAA A&P Airframe Inspection
  • Documentation = Traceability: Every inspection, repair, and AD compliance must be documented per 14 CFR 43.9. This ensures traceability and legal compliance.
  • Safety-Critical Items = Immediate Action: Items such as control cables, landing gear components, fuel leaks, and engine chip detectors require immediate corrective action. Deferring these items is not acceptable.
Safety-Critical Items Require Immediate Action - No Deferral AIRFRAME INSPECTION — SAFETY-CRITICAL ITEMS: IMMEDIATE ACTION 14 CFR §91.7 · AC 43.13-1B · ACS Inspection Standards DISCREPANCY LIST CONTROL CABLE Fraying > 15% of diameter (AC 43.13-1B §7-143) CRITICAL LANDING GEAR ACTUATOR Hydraulic fluid leak — gear retraction system CRITICAL FUEL SYSTEM Fuel leak at wing root — fire hazard CRITICAL ENGINE CHIP DETECTOR Metal particles detected — bearing failure risk CRITICAL SKIN PANEL Minor surface corrosion — treat per AC 43.13-1B §6-15 SCHEDULED CABIN INTERIOR Trim panel wear — cosmetic, no airworthiness effect ROUTINE ACTION QUEUE — IMMEDIATE PRIORITY 1. CONTROL CABLE — REPLACE No deferral permitted · Ground aircraft immediately 2. LANDING GEAR — REPAIR No deferral permitted · Gear down-lock safety 3. FUEL LEAK — REPAIR No deferral permitted · Fire hazard 4. CHIP DETECTOR — INVESTIGATE No deferral permitted · Engine teardown inspection 5. SKIN CORROSION — TREAT Next scheduled maintenance · 100-hr inspection 6. TRIM WEAR — REPLACE Next annual inspection · Cosmetic ⚠ NO DEFERRAL — SAFETY-CRITICAL ITEMS REQUIRE IMMEDIATE CORRECTIVE ACTION AC 43.13-1B §1-5 · 14 CFR §91.7(a) — No person may operate a civil aircraft unless it is in an airworthy condition Immediate Action Required Scheduled Maintenance Routine
  • Allowable Limits = Context-Specific: The allowable limits for damage (e.g., cracks, corrosion, broken wires) depend on the component and its function. Primary flight control cables have zero tolerance for broken wires, while secondary cables may have a 15% limit. The mechanic must always consult the manufacturer's data or AC 43.13-1B.

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