05/04/2025
A CHECK – Light Check (Line Maintenance)
Interval: Every 400–600 flight hours or ~1–2 months
Downtime: 6 to 24 hours
Where: Performed at line stations or hangars
Aircraft Interior:
Check passenger seats, oxygen masks, cabin lighting
Emergency equipment inspection (life vests, fire extinguishers)
Cockpit
System BITE (Built-In Test Equipment) checks
CVR (Cockpit Voice Recorder) & FDR (Flight Data Recorder) test
Engines & APU
Oil levels, leaks, fan blade inspection
APU operational test
Landing Gear
Tire pressure, brake wear, strut extension
Avionics (B2 role)
Navigation/communication test
Fault memory check
Fluids & Filters
Replenish hydraulic, engine oil, potable water
Replace filters if needed
B CHECK – Intermediate Check (Rare in Modern Programs)
Interval: Every 6–8 months
Downtime: 1 to 3 days
Key Tasks:
Includes all A-check tasks plus:
Systems Functional Checks:
Electrical systems
Avionics & air data computers
Auto flight & autopilot system tests
Flight Controls & Hydraulic Systems:
Movement check
Hydraulic leak checks
Lubrication & Cleaning:
Deeper cleaning of components
Lubrication of hinges, latches, actuators
Corrosion Prevention:
Initial inspection and treatment for visible corrosion
Note: Many airlines integrate B-check items across multiple A-checks.
C CHECK – Heavy Check (Base Maintenance)
Interval: Every 18–24 months or 6,000 flight hours/cycles
Downtime: 1 to 2 weeks
Where: Performed in large hangars with extensive support tools
Key Tasks:
All A + B-check tasks, plus:
Structural Inspections:
Fuselage skin, wing root, empennage, cargo areas
High-intensity corrosion and fatigue inspection
Systems Overhaul:
Air conditioning, pressurization, fire protection systems
Oxygen generation and distribution system tests
Landing Gear & Brakes:
Detailed visual and NDT (non-destructive testing)
Brake unit removal and inspection
Flight Controls & Actuators:
Detailed check of control surfaces, hinges, actuators
Avionics Systems:
Deep fault analysis, updates, and calibration
Full inspection of TCAS, GPWS, ELT, NAV systems
Interior Refurbishment:
Replacement of worn panels, carpet, and passenger systems
D CHECK – Heavy Maintenance Visit (HMV)
Interval: Every 6–10 years
Downtime: 4 to 8 weeks
Where: Specialized heavy maintenance or overhaul facilities
Key Tasks:
Complete aircraft disassembly and teardown
Structure:
Paint removal for complete fuselage inspection
Detailed NDT checks for cracks, corrosion, fatigue
Repairs, modifications, or structural replacements
Engines:
Complete engine removal, borescope, and overhaul (if needed)
Landing Gear:
Full overhaul or exchange of landing gear components
Wiring & Avionics (B2 intensive work):
Routing inspection, continuity checks, replacement
System reprogramming and software upgrades
Cabin:
Major interior refurbishment – new seats, galleys, lavs
Compliance:
Major Service Bulletins (SBs), Airworthiness Directives (ADs), modifications