Aircraft maintenance is organized by assembly type and event type. Each assembly—the airframe, engines, landing gear, auxiliary power unit (APU), hydraulic systems, and others—has its own maintenance schedule. Understanding which events apply to which assemblies is critical for maintenance planning, cost estimation, and workforce scheduling.
This guide covers every major maintenance event in modern commercial aviation and which aircraft assemblies they affect.
How to Read This Guide
Each maintenance event includes:
- What it is: The technical definition and purpose
- Typical duration: How long the event takes (varies by aircraft type)
- Key dependencies: Factors affecting when/how the event is performed
- Affected assemblies: Which aircraft systems are involved
- Synonyms: Alternative names for the same event
- Tools & skills required: What technicians need
1. AIRFRAME MAINTENANCE EVENTS
The airframe is the aircraft's fuselage, wings, tail, and control surfaces. Airframe events are structural and surface-focused.
A-Check (Line Check / Walk-Around)
What it is: Visual exterior and interior inspection; the most frequent maintenance event. Technicians walk around and through the aircraft looking for obvious damage, fluid leaks, and wear.
Typical duration: 1–2 hours (can be as quick as 30 minutes for regional aircraft)
Frequency: Every 400–600 flight hours (roughly every 1–2 weeks for commercial airliners)
Key dependencies: - Aircraft flight hours logged since last A-check - Aircraft type (larger aircraft take longer) - Hangar availability (some A-checks done between flights at the gate) - Weather (difficult in heavy rain or snow)
Affected assemblies: - Fuselage and skin - Windows and doors - External lights - Tires and brakes (visual inspection only) - Antennas and probes - Paint condition
Synonyms: Line check, walk-around inspection, pre-flight inspection (PRAT), ramp check
Tools & skills: - Visual inspection training - Knowledge of aircraft exterior components - Ability to spot cracks, corrosion, fastener issues - No specialized equipment (except flashlight)
B-Check (Intermediate Check)
What it is: Deeper than A-check; includes removal of some components for inspection and lubrication of moving parts. This is where corrosion inspection begins in earnest.
Typical duration: 10–20 hours (overnight or 1–2 days)
Frequency: Every 1,200–2,000 flight hours (roughly every 2–4 months)
Key dependencies: - Accumulated flight hours - Aircraft age (older aircraft may have more corrosion, extending duration) - Maintenance history (previous findings require follow-up) - Hangar availability - Weather conditions
Affected assemblies: - Fuselage skin and structure - Control surfaces (ailerons, elevators, rudder) - Landing gear (visual; not removed) - Hydraulic lines - Fuel system components - Door seals and mechanisms - Wheel wells and undercarriage (high corrosion zones)
Synonyms: Intermediate maintenance check, hangar check, 1,200-hour check
Tools & skills: - Borescope (fiber-optic camera for internal inspection) - Lubricating tools and grease - Fastener inspection knowledge - Corrosion identification and surface treatment
C-Check (Heavy Maintenance Check / Overhaul)
What it is: Major structural inspection and component removal/replacement. The airframe is partially disassembled: engines come out, landing gear comes out, panels are removed to access internal structure.
Typical duration: 400–800 labor hours (1–4 weeks of elapsed time, depending on hangar workflow)
Frequency: Every 18–24 months (or 4,000–6,000 flight hours)
Key dependencies: - Accumulated flight hours and cycles (takeoffs/landings; cycles matter more than hours for structural fatigue) - Aircraft age and corrosion extent - Previous maintenance findings (carryover issues) - Availability of specialized facilities and parts - Engine overhaul timelines (engines often sent out for overhaul during C-check) - Paint and cabin refurbishment scope
Affected assemblies: - Entire fuselage (major disassembly and inspection) - Wings and control surfaces (removed, inspected, reinstalled) - Tail section - Landing gear (removed, sent to overhaul facility) - Engines (removed, sent to engine shop or overhauled in-house) - Hydraulic systems (hoses replaced, fluid flushed) - Fuel system (filters replaced, tanks inspected) - Avionics racks (some removed for access) - Cabin (seats, carpets, galleys, toilets refreshed)
Synonyms: Heavy check, C-maintenance, major maintenance visit (MMV), scheduled event check, rinse-and-repeat
Tools & skills: - Ultrasonic inspection for fatigue cracks - Borescope and other non-destructive testing (NDT) - Structural fastener removal/replacement - Paint stripping and application - Engine removal/installation procedures - Landing gear overhaul procedures - Hydraulic system maintenance - Avionics rigging and functional checks
D-Check (Overhaul / Major Structural Inspection)
What it is: Complete airframe overhaul. The aircraft is essentially taken to pieces: fuselage is split, wings are removed, internal structures are fully inspected for fatigue cracks. This is the deepest inspection short of rebuilding.
Typical duration: 1,500–3,000 labor hours (30–90 days of elapsed time; sometimes 3–6 months for complex aircraft)
Frequency: Every 6–10 years (or 20,000–30,000 flight hours)
Key dependencies: - Aircraft age (older aircraft may require extended scope) - Corrosion severity (salt-water exposure increases scope) - Cycle count (structural fatigue depends on pressurization cycles, not just hours) - Fatigue findings from previous checks - Regulatory changes (new inspection standards may be required) - Major component overhaul requirements (landing gear, engines, flight controls) - Availability of specialized D-check facilities (limited globally)
Affected assemblies: - Complete fuselage (often split and joined with new rivets/fasteners) - Wings (removed, fully inspected) - Tail section (removed, inspected) - Landing gear (overhauled or replaced) - Engines (full overhaul or replacement) - Hydraulic systems (complete system inspection and rebuild) - Fuel system (complete inspection and replacement of degraded components) - Electrical systems (wiring harnesses inspected, some replaced) - Flight controls (cables inspected, actuators overhauled) - Avionics (major upgrade opportunity)
Synonyms: D-maintenance, major overhaul, structural overhaul, airframe restoration, rinse-and-repeat-deep, level 4 maintenance
Tools & skills: - Ultrasonic and eddy-current inspection equipment - Borescope and videoscope - Structural repair procedures (metal bonding, fatigue crack repair) - Fuselage splitting/joining (requires specialized training) - Paint stripping (often chemical or abrasive; environmental hazards) - Specialized riveting and fastening - Life-limited parts replacement (engines, gear assemblies) - Regulatory compliance audits - Weight and balance recalculation
2. ENGINE MAINTENANCE EVENTS
Aircraft engines are highly regulated, high-wear components. Engine maintenance is separated from airframe maintenance because engines can be removed, overhauled, and reused on different aircraft.
Engine Borescope Inspection (Borescope Check)
What it is: Visual inspection of engine turbine blades and combustor without removing the engine. A fiber-optic camera is inserted through an access port to photograph blade condition.
Typical duration: 2–4 hours
Frequency: Every B-check (1,200–2,000 flight hours) or after a suspected hot event (FOD, bird strike, overheat)
Key dependencies: - Engine operating hours since last borescope - History of high-temperature events or compressor damage - Engine deterioration trend (tracked over time) - Availability of borescope equipment - Technician certifications (borescope interpretation requires training)
Affected assemblies: - High-pressure compressor blades - Compressor rotors and casings - Combustor (combustion chamber) - Turbine blades and rotors - Engine inlet
Synonyms: Borescope check, blade inspection, visual turbine inspection, compressor inspection, FOD check, hot-end inspection
Tools & skills: - Borescope equipment (flexible or rigid fiber-optic camera) - Borescope interpretation training - Knowledge of blade defects (cracks, erosion, leading-edge damage, rubs) - Photography/documentation skills - Engine teardown procedures (if damage found)
Engine On-Condition Maintenance (OCM / ECS - Engine Condition Screening)
What it is: Monitoring of engine health parameters (vibration, oil analysis, temperature trends) to predict when overhaul is needed. Engines are kept in service until they drift out of limits, rather than removed on a fixed schedule.
Typical duration: Continuous monitoring; decision made when parameters exceed limits
Frequency: Constant (data collected every flight)
Key dependencies: - Baseline parameters established during initial build/overhaul - Ambient temperature and humidity (affects sensor readings) - Aircraft utilization and flight profile (long vs. short flights) - Engine age and prior overhaul history - Availability of analysis software (airlines subscribe to engine monitoring services)
Affected assemblies: - Engine bearings (vibration indicates wear) - Fuel nozzles and combustor (combustion efficiency monitored) - Turbine section (temperature margins indicate deterioration) - Compressor (pressure ratio trends) - Oil system (particulate analysis shows metal wear)
Synonyms: Engine condition monitoring (ECM), engine health management (EHM), on-condition maintenance, condition-based maintenance (CBM), engine trend monitoring, EASA-mandated engine monitoring
Tools & skills: - Engine Parameter Monitoring System (EPMS) software - Oil analysis (spectroscopy to detect metal particles) - Vibration analysis - Trend interpretation - Threshold setting and alert management - Communication with engine manufacturer (OEM) for guidance
Engine Removal (Hot Section Inspection / HSI)
What it is: Engine is removed from aircraft and sent to a specialized engine overhaul shop (also called an "engine shop" or "engine MRO"). The engine's hot section (turbine and combustor) is inspected and worn components are replaced.
Typical duration: 2–4 weeks (removal + overhaul + reinstallation) for a hot-section inspection; up to 8 weeks for a full engine overhaul
Frequency: Triggered by on-condition monitoring limits being exceeded, or every 5–8 years for preventive reasons (varies by engine model and airline policy)
Key dependencies: - Engine on-condition parameters (vibration, temperatures, efficiency) - Spare engine availability (airline must have a loaner or leased engine) - Engine shop capacity (major MROs may have long lead times) - Shipping and logistics (engines are valuable; transportation is tracked) - Regulatory approval (EASA or FAA must approve the overhaul plan) - Core exchange agreements (airlines often trade old engines for credit toward overhaul costs)
Affected assemblies: - High-pressure turbine (HPT) rotor and stator - Low-pressure turbine (LPT) rotor and stator - Combustor and fuel nozzles - Compressor rotor (if damage detected) - Bearings and seals - Oil system
Synonyms: Hot-section overhaul (HSO), hot-section inspection, engine overhaul, engine removal, engine shop visit (ESV), major shop visit (MSV), full-flight-hour overhaul
Tools & skills: - Engine removal/installation procedures - Borescope interpretation (decides if full overhaul or hot-section only) - Spare engine documentation and tracking - Core exchange agreements - Regulatory submission and approval - Engine technician skills (at the shop, not the airline)
Engine Run / Full-Authority Digital Engine Control (FADEC) Test
What it is: After engine overhaul or replacement, the engine is started and operated at various thrust levels to verify correct operation before flight.
Typical duration: 1–2 hours (includes warm-up, idle checks, climb power checks, thrust-reverse test if equipped)
Frequency: Mandatory after any engine removal, replacement, or major overhaul; optional trending on some airlines as part of condition monitoring
Key dependencies: - Hangar availability with engine run capability (not all hangars are sound-insulated for engine starts) - Fuel availability (jet fuel needed; sometimes special high-sulfur test fuel used) - Weather (low wind preferred; some restrictions on rain/lightning) - Engine parameters baseline (from previous runs or OEM data) - FADEC software version (engine computer must be verified)
Affected assemblies: - All engine systems (fuel, oil, hydraulics, combustor, turbines) - Engine bleed air system - Anti-ice systems - Engine fire detection
Synonyms: Engine run, engine test, power check, FADEC test, engine acceptance, post-overhaul test, performance baseline run
Tools & skills: - Engine Parameter Display System (EPDS) or cockpit interface - Engine manual operation procedures - Fuel management - Sound-insulated facility - Engine technician certification
3. LANDING GEAR MAINTENANCE EVENTS
Landing gear is a complex assembly subject to high stresses during landing and taxiing. Gear maintenance is separated from airframe work because gear is often removed and overhauled at specialized shops.
Landing Gear Visual Inspection (B-Check)
What it is: Technician visually inspects landing gear while aircraft is on stands (jacked up). No removal. Inspection covers tires, brakes, hydraulic lines, and structural integrity.
Typical duration: 1–2 hours per gear (nose and main landing gears)
Frequency: Every B-check (1,200–2,000 flight hours)
Key dependencies: - Flight hours and landing cycles (cycles stress gear more than hours) - Weather (corrosion risk in coastal/humid areas) - Tire condition (tires wear faster with hard landings) - Brake wear (measured by wear indicators) - Previous damage history
Affected assemblies: - Main landing gear struts (shock struts) - Nose landing gear - Wheels and tires - Brake assemblies - Hydraulic lines and fittings - Uplock/downlock mechanisms - Gear doors
Synonyms: Landing gear check, undercarriage inspection, gear visual inspection, strut inspection, wheel and brake check
Tools & skills: - Aircraft jacking equipment - Hydraulic line inspection - Tire pressure and tread measurement - Brake wear indicator reading - Corrosion identification
Landing Gear Overhaul (Off-Aircraft)
What it is: Landing gear is removed from aircraft and sent to a specialized landing gear overhaul facility. Every component—struts, cylinders, seals, fasteners, actuators—is inspected, cleaned, and worn parts replaced.
Typical duration: 4–8 weeks (removal + shop work + reinstallation)
Frequency: Every 6–10 years, or triggered by overhaul limits (e.g., 10,000 landing cycles)
Key dependencies: - Landing cycles accumulated (more important than flight hours for gear) - Aircraft age - Maintenance findings from visual inspections - Gear shop capacity (fewer facilities than engine shops) - Spare gear availability (spares may need to be leased) - Corrosion extent (salt exposure accelerates overhaul need)
Affected assemblies: - Main and nose gear struts - Hydraulic cylinders - Wheels and hubs - Brake components - Actuators and linkages - Uplock/downlock mechanisms - Fasteners and seals
Synonyms: Landing gear overhaul, gear overhaul, undercarriage overhaul, strut overhaul, gear shop visit, major gear overhaul
Tools & skills: - Gear removal/installation - Spare gear documentation - Gear shop coordination - Regulatory documentation
Tire and Brake Assembly Maintenance
What it is: Tires and brake discs are wear items replaced at intervals based on wear depth, damage, or landing cycle limits.
Typical duration: 1–3 hours per landing gear (nose and main)
Frequency: Tires every 300–600 landings (depends on tire type and aircraft weight); brakes when wear indicators show minimum thickness
Key dependencies: - Aircraft landing weight (heavier landings wear tires/brakes faster) - Landing technique (hard landings accelerate wear) - Runway conditions (rough pavement accelerates wear) - Aircraft type (regional aircraft have more frequent tire changes than widebodies)
Affected assemblies: - Wheels (rims and hubs) - Tires (pneumatic) - Brake discs and linings - Brake actuators
Synonyms: Tire change, brake disc replacement, wheel maintenance, brake assembly replacement, consumables maintenance
Tools & skills: - Tire removal/installation equipment - Brake lining measurement - Wheel balancing (sometimes) - Corrosion treatment (for rims)
4. AUXILIARY POWER UNIT (APU) MAINTENANCE EVENTS
The APU is a small turbine engine mounted in the aircraft tail that provides electrical power and pneumatic (bleed) air when the main engines are off.
APU Visual Inspection
What it is: External inspection of APU inlet, exhaust, and access panels for damage, cracks, or leaks. No removal.
Typical duration: 30 minutes–1 hour
Frequency: Every B-check (1,200–2,000 flight hours)
Key dependencies: - APU operating hours - Engine deterioration trend (monitored via borescope) - History of APU faults or shutdowns - Salt-water exposure (coastal corrosion)
Affected assemblies: - APU inlet and outlet ducts - Fuel system supply line - Oil system - Bleed air outlet - Electrical generation components
Synonyms: APU check, auxiliary power unit inspection, APU inlet inspection
APU Borescope Inspection
What it is: Same as engine borescope; a camera is inserted to visually inspect APU turbine blades for damage, cracks, or erosion.
Typical duration: 1–2 hours
Frequency: Every 500–1,000 APU operating hours, or after an APU shutdown event
Key dependencies: - APU operating hours (less than main engines; regional aircraft use APU more) - History of borescope findings - Availability of borescope equipment compatible with APU
Affected assemblies: - APU compressor and turbine blades - Combustor - Inlet guide vanes
Synonyms: APU borescope check, APU blade inspection, APU hot-end inspection
APU Removal and Overhaul
What it is: APU is removed from aircraft and sent to an overhaul facility. The APU is similar to an engine but smaller; overhaul is similar to engine overhaul.
Typical duration: 6–12 weeks (removal + overhaul + reinstallation)
Frequency: Every 15,000–20,000 operating hours, or triggered by on-condition parameters
Key dependencies: - APU operating hours - Borescope findings - On-condition parameter trends (vibration, pressure ratios) - Spare APU availability
Affected assemblies: - All APU components (compressor, combustor, turbine, bearings)
Synonyms: APU overhaul, APU removal, APU major shop visit
5. LIFE-LIMITED PARTS (LLPs) MAINTENANCE EVENTS
Life-limited parts are components designed to be replaced after a specific number of flight hours, cycles, or calendar days—regardless of condition. These parts are critical to safety.
Life-Limited Parts Tracking and Replacement
What it is: Systematic monitoring and replacement of parts with finite service lives. Each LLP has a "hard time limit" (e.g., 10,000 flight hours or 5,000 landings).
Typical duration: Varies (minutes for small parts; hours for major assemblies like landing gear)
Frequency: Continuous tracking; replacement when limit is reached
Key dependencies: - Aircraft utilization rate (affects when limits are reached) - Spare parts availability (must be in stock or on order) - Regulatory requirements (vary by type certificate and jurisdiction) - Maintenance planning (LLP replacements must be coordinated with other events)
Affected assemblies: - Engines: High-pressure rotors, turbine discs (often limited to 20,000–40,000 flight hours) - Landing gear: Strut cylinders, actuators (often 10,000–15,000 landing cycles) - Flight controls: Actuator cylinders (5,000–10,000 hours) - Hydraulic components: Seals and valve bodies (time-based limits) - Fasteners: Some critical fasteners have time limits - Pressure vessels: Air bottles, accumulators (10–15 years calendar time)
Synonyms: LLP replacement, hard-time limits, scheduled replacement, critical component tracking, life-expended parts
Tools & skills: - Maintenance planning software (tracks LLP status for each aircraft) - Parts traceability (serialization, documentation) - Regulatory knowledge (what qualifies as LLP) - Coordination with supply chain
6. HYDRAULIC SYSTEM MAINTENANCE EVENTS
Aircraft hydraulic systems power everything from flight controls to landing gear to brakes. Hydraulics maintenance is critical for safety.
Hydraulic Fluid Sampling and Analysis
What it is: A small sample of hydraulic fluid is drawn from the system and analyzed for contamination (water, metallic particles, debris). High contamination indicates pump wear or seal degradation.
Typical duration: 30 minutes (sampling); analysis takes 2–5 days
Frequency: Every 500–1,000 flight hours, or every B-check
Key dependencies: - Fluid contamination baseline (varies by aircraft age) - Historical trends (rising particle count indicates problems) - Filter service (filters capture most contaminants but degrade over time) - System history (previous failures or repairs)
Affected assemblies: - Hydraulic pump - Hydraulic motor (flight control actuators) - Reservoir and filtration
Synonyms: Hydraulic fluid analysis, fluid sampling, condition monitoring, oil analysis, contamination check
Tools & skills: - Fluid sampling kit (sterile sampling technique) - Lab access (external lab or on-site capability) - Particle counting and water content measurement - Trend interpretation
Hydraulic Fluid Flushing and Replacement
What it is: Complete hydraulic fluid is drained and replaced with fresh fluid. The system is flushed with cleaning fluid first to remove contaminants.
Typical duration: 8–16 hours (flushing + drying + refilling + testing)
Frequency: Every 3–5 years, or triggered by high contamination levels
Key dependencies: - Fluid age (hydraulic fluid degrades over time) - Contamination levels (high levels require flushing) - System pressure test results - Regulatory requirements (some systems require flushing at regular intervals)
Affected assemblies: - Entire hydraulic system (pump, motors, actuators, lines, reservoir)
Synonyms: Hydraulic system flush, fluid replacement, system purge, contamination removal
Tools & skills: - Flushing equipment (portable or mobile units) - System depressurization and drying - Fluid specification knowledge - Pressure testing
Hydraulic Hose and Line Inspection / Replacement
What it is: Visual and pressure testing of hydraulic hoses and metal lines for leaks, cracks, corrosion, or kinks. Hoses are replaced when nearing end of service life (typically 5–10 years).
Typical duration: 2–8 hours (depending on number of hoses)
Frequency: Visual inspection every B-check; replacement every 5–10 years
Key dependencies: - Hose age and service life limits - Corrosion (salt water exposure) - Pressure test history - Proximity to hot components (heat degrades hose material)
Affected assemblies: - Flight control actuators - Landing gear actuators - Wheel brake lines - Engine bleed air isolation lines
Synonyms: Hose inspection, line replacement, hose leakage test, pressure test, hose assembly change
Tools & skills: - Hydraulic pressure testing equipment - Hose specification knowledge - Corrosion identification - Leak detection (visual, ultrasonic, or dye)
7. PNEUMATIC SYSTEM MAINTENANCE EVENTS
Pneumatic (bleed air) systems supply high-pressure compressed air from engines or APU for anti-ice, pneumatic starters, and cabin pressurization.
Pneumatic System Inspection and Leak Testing
What it is: Visual inspection of pneumatic lines, isolation valves, and dump valves for leaks, kinks, or corrosion. Pressure testing verifies system holds air without loss.
Typical duration: 1–3 hours
Frequency: Every B-check (1,200–2,000 flight hours) or if cabin pressurization issues reported
Key dependencies: - System operating pressure (varies by altitude and aircraft configuration) - Cabin pressurization function (critical for safety) - History of pressurization problems - Environmental corrosion (salt water, humidity)
Affected assemblies: - Engine bleed air valves - Pneumatic lines and distribution valves - Anti-ice system - Cabin pressurization controller - Air inlet isolation valve
Synonyms: Pneumatic system check, bleed air inspection, pressurization system test, cabin pressure test
Tools & skills: - Pressure testing equipment - Leak detection methods (soap bubble test, ultrasonic) - Valve operation verification - System troubleshooting
8. AVIONICS AND ELECTRICAL SYSTEM MAINTENANCE
Avionics Line Replacement Test (LRT / System Functional Test)
What it is: Avionics systems (navigation, autopilot, weather radar, flight management system) are tested on a regular basis to verify they are functioning correctly. Some tests require flight testing; others are ground tests.
Typical duration: 2–8 hours (ground tests); longer for in-flight functional checks
Frequency: Every C-check or D-check, or annually for some systems (depending on regulatory requirements)
Key dependencies: - Avionics age and reliability history - Software updates (some systems require updates as part of testing) - Ground support equipment availability - Regulatory requirements (EASA Part-M requires periodic functional checks)
Affected assemblies: - Flight management system (FMS) - Inertial reference unit (IRU) - Navigation systems (IRS, GPS) - Autopilot system - Weather radar - Terrain awareness and warning system (TAWS) - Traffic collision avoidance system (TCAS)
Synonyms: Avionics functional check, system test, avionics validation, LRT (line replacement test), in-flight check
Tools & skills: - Ground support equipment (computers, test adapters) - Avionics system knowledge - Troubleshooting procedures - FAA/EASA functional check requirements
Electrical System Inspection and Component Replacement
What it is: Wiring harnesses, connectors, circuit breakers, and electrical distribution boxes are inspected for corrosion, loose connections, or sign of overheating. Aging components are replaced.
Typical duration: 4–16 hours (depending on scope)
Frequency: Every C-check or D-check; more often if corrosion issues found
Key dependencies: - Aircraft age (older wiring is more prone to failure) - Environmental exposure (salt water, humidity accelerate corrosion) - Electrical system load (heavily used systems fail sooner) - Historical failures (repeat problems trigger preventive replacement)
Affected assemblies: - Main electrical distribution panel - Wiring harnesses - Connectors and junction boxes - Circuit breakers - Relays and contactors - Battery/APU electrical generation
Synonyms: Electrical system maintenance, wiring inspection, electrical connector replacement, corrosion prevention, harness replacement
Tools & skills: - Continuity and voltage testing - Connector inspection and cleaning - Corrosion identification and treatment - Wiring diagram knowledge
9. STRUCTURAL INSPECTION AND CORROSION CONTROL
Corrosion Inspection (Cadmium Plating, Fastener Corrosion)
What it is: Aircraft use cadmium-plated fasteners and aluminum-alloy skins. Both corrode over time, especially in salt-water environments. Inspectors visually identify corrosion, treat it with chemical compounds, and replace badly corroded fasteners.
Typical duration: 4–16 hours (varies by extent of corrosion)
Frequency: Every B-check; intensive inspection every C-check
Key dependencies: - Aircraft age - Operating environment (salt water exposure) - Humidity and temperature cycling - Previous corrosion treatment history
Affected assemblies: - Fuselage skin - Wing skin - Fasteners (screws, rivets, bolts) - Landing gear attach points - Undercarriage (wheel wells, fuel tank areas)
Synonyms: Corrosion check, fastener inspection, cadmium inspection, undercarriage corrosion survey, salt-water corrosion
Tools & skills: - Visual inspection training - Corrosion grading standards (EASA AC 20-77A) - Chemical treatment application - Fastener replacement procedures - Environmental safety (handling corrosion treatments)
Fatigue Crack Inspection (Ultrasonic, Eddy-Current)
What it is: Non-destructive testing (NDT) methods are used to detect tiny cracks in metal structures caused by repeated stress cycles. Ultrasonic and eddy-current tools can find cracks invisible to the eye.
Typical duration: 4–24 hours (depending on inspection scope and aircraft size)
Frequency: Every D-check; as needed after incidents or high-cycle usage
Key dependencies: - Aircraft age and cycle count (more cycles = more fatigue) - Previous inspection findings (repeat inspections in high-risk areas) - Manufacturer service bulletins (may mandate inspections after X cycles) - NDT technician availability (requires special certification)
Affected assemblies: - Wing root (high-stress junction) - Fuselage around cabin doors - Fuselage around landing gear attachment - Tail section attachment - Engine mount points
Synonyms: NDT inspection, fatigue crack detection, ultrasonic inspection, eddy-current inspection, structural integrity check
Tools & skills: - Ultrasonic inspection equipment - Eddy-current equipment - NDT technician certification (ASNT Level 2 or 3) - Fatigue crack repair procedures (if cracks found)
10. CABIN AND INTERIOR MAINTENANCE
Cabin Refurbishment (Seats, Carpets, Galleys, Lavatories)
What it is: Interior components—seats, carpets, wall panels, overhead bins, galleys, and lavatories—are inspected, cleaned, repaired, or replaced to maintain passenger comfort and safety.
Typical duration: 20–100 hours (light refresh) to 200+ hours (complete overhaul)
Frequency: Every C-check (partial refresh); every D-check or every 8–12 years (major overhaul)
Key dependencies: - Aircraft utilization (high-utilization aircraft wear interior faster) - Passenger comfort standards (airlines vary in refurbishment policies) - Regulatory requirements (some safety items mandatory) - Supplier availability (custom seat covers, carpet, etc.)
Affected assemblies: - Seats and seat tracks - Carpets and flooring - Wall panels and lighting - Galleys and ovens - Lavatory fixtures - Overhead bins and doors - Emergency slide containers
Synonyms: Cabin refurbishment, interior refresh, cabin aesthetic renewal, cabin configuration change, seating overhaul
Tools & skills: - Upholstery repair/replacement - Carpet installation - Electrical work (lighting, galley power) - Safety system checks (emergency slides, lighting)
11. SPECIALIZED EVENTS BY AIRCRAFT TYPE
Cargo Door Inspection and Lubrication
Cargo aircraft have large doors that open hydraulically. Doors require regular lubrication and inspection to prevent jamming.
Typical duration: 2–4 hours Frequency: Every 500–1,000 flight hours
Fuel Tank Borescope Inspection
Large widebody aircraft have fuel tanks inspected via borescope to look for corrosion, sediment, and contamination.
Typical duration: 4–6 hours Frequency: Every C-check or every 5 years
Windscreen and Window Inspection/Replacement
Aircraft windscreens and cabin windows must meet airworthiness standards. Scratches, cracks, or delamination require replacement.
Typical duration: 1–2 hours per window Frequency: As needed (no fixed interval) or every C-check (refresh seals)
Summary: Maintenance Event Timeline
Here's a typical aircraft maintenance schedule over a 10-year period:
YEAR 1, MONTH 6:
├─ A-checks (every 400-600 FH) — Every 1-2 weeks
└─ B-check (around 1,200 FH) — 2-4 month interval
YEAR 1, MONTH 18:
├─ A-checks continue
├─ B-checks continue (2-4 month interval)
└─ C-check (first major visit) — 4-8 weeks off-wing
YEAR 3:
├─ Multiple B-checks
└─ Second C-check — 4-8 weeks
YEAR 5-6:
├─ B-checks (routine)
├─ Third C-check — 4-8 weeks
├─ Landing gear overhaul (if cycle limits reached)
├─ Engine hot-section overhaul (if OCM trending poor)
└─ LLP replacements (as limits reached)
YEAR 8-10:
├─ Routine B-checks
├─ Fourth C-check
└─ D-Check (major overhaul) — 6-12 weeks off-wing
(fuselage inspection, complete system overhaul)
Key Takeaways for Maintenance Professionals
- A-checks are frequent, routine, short-duration events that prevent major issues
- B-checks begin deeper inspection and component lubrication
- C-checks are where major structural and engine work happens; plan 1–4 weeks of downtime
- D-checks are rare but comprehensive; may require sending aircraft to specialized facilities
- Engine, landing gear, and APU maintenance can be done on-aircraft (visual/borescope) or off-aircraft (overhaul)
- Life-limited parts require continuous tracking; replacement is mandatory when limits expire
- Corrosion and fatigue are the biggest drivers of maintenance costs; prevention is critical
- Maintenance planning must coordinate multiple events (A, B, C-checks with LLP replacements, engine overhauls, etc.) to minimize aircraft downtime
Resources and References
- EASA Part-M: Maintenance and Airworthiness
- FAA Part 145: Maintenance Organization Certification
- ATA iSpec 2200: Maintenance Program Development
- Engine Manufacturer Documentation (Rolls-Royce, General Electric, Pratt & Whitney)
- Landing Gear OEM Manuals (Dunlop Aerospace, Meggitt, Goodrich)
- Aircraft Maintenance Training (CAMET, ATECH, and in-house airline programs)