February 26, 2025

Steven Bentley

Sofema Aviation Services (SAS) considers key tasks which are applicable candidates for Critical Maintenance Tasks Inspection.

These tasks are examples and will vary based on aircraft type, operator-specific requirements, and maintenance program. EASA requires risk assessment and procedural controls to ensure critical maintenance tasks are performed correctly, including independent inspections. Human factors are critical in managing these tasks to avoid errors.

Flight Control Systems

  • Installation, adjustment, or repair of flight control surfaces (e.g., ailerons, elevators, rudders).
  • Rigging, cable tension checks, and system alignment.
  • Actuator replacement or repair.

Landing Gear Systems

  • Retraction/extension system maintenance.
  • Wheel, tire, and brake replacement.
  • Installation and adjustment of landing gear locking mechanisms.

Powerplant Installation

  • Installation and securing of aircraft engines and nacelles.
  • Thrust reverser installation or adjustment.
  • Engine mount inspections and torque checks.

Fuel Systems

  • Replacement of fuel lines, fittings, or components.
  • Sealing, testing, and inspection of fuel tanks for leaks.
  • Installation of fuel pumps, filters, or related components.

Aircraft Structure

  • Repairs or replacement of primary structural elements (e.g., fuselage frames, wing spars).
  • Critical bonding or riveting operations.
  • Repairs to pressure bulkheads or skin.

Electrical Systems

  • Installation or reinstallation of critical wiring bundles or harnesses.
  • Replacement or adjustment of generators, alternators, and main power supplies.
  • Battery system installation and testing.

Emergency Systems

  • Inspection and testing of emergency systems (e.g., slides, flotation devices, oxygen systems).
  • Installation of fire detection and extinguishing systems.
  • Testing of ELT (Emergency Locator Transmitter).

Hydraulic Systems

  • Replacement or adjustment of hydraulic pumps, actuators, or servo-controls.
  • Hydraulic line inspections and repairs.
  • System bleeding, flushing, and pressure testing.

Avionics Systems

  • Installation or testing of autopilot or flight management systems (FMS).
  • Critical inspections of communication and navigation systems.
  • Replacement or calibration of altimeters and transponders.

Propeller Systems

  • Installation or adjustment of propellers.
  • Blade angle checks and torque verification.
  • Inspection or replacement of de-icing systems on propellers.

Pressurization Systems

  • Replacement or adjustment of cabin pressure control valves.
  • Testing and calibration of outflow valves.
  • Sealing of pressure vessel components.

Safety-Critical Inspections

  • Inspections following a heavy landing or significant turbulence event.
  • Damage assessment for bird strikes or lightning strikes.
  • Critical non-destructive testing (NDT) of structural areas.

Example Critical Maintenance Tasks taken from an approved MOE

General

  • Major modification
  • CDCCL tasks
  • Works involving swarf, chips, or debris with contamination risks
  • Re-routing aircraft cables and harnesses
  • Aircraft software upload and configuration checks

Air Conditioning (ATA 21)

  • Leak/pressurization test after assembly
  • Repair or replacement of pressurization system components

Auto Flight (ATA 22)

  • Replacement of components requiring adjustment

Communications (ATA 23)

  • CVR installation and adjustments/tests after rectification

Electrical Power (ATA 24)

  • Repair of electrical wiring, harness, or connectors
  • Replacement of main batteries and IDG filters

Equipment/Furnishing (ATA 25)

  • Installation of flight crew seats and escape slides
  • Cabin seat installation (more than three rows removed)

Fire Protection (ATA 26)

  • Replacement of fire extinguisher bottles and cartridges

Flight Controls (ATA 27)

  • Removal/installation of flight control surfaces, cables, or actuators
  • Adjustments and defect rectifications involving major components

Fuel System (ATA 28)

  • Fuel quantity system adjustment after repairs
  • Leak tests and fuel shutoff valve installations

Hydraulic System (ATA 29)

  • Removal/installation of hydraulic fuses
  • Leak tests after repairs or component replacement

Indicating/Recording (ATA 31)

  • Replacement of main cockpit instruments and DFDR installations

Landing Gear (ATA 32)

  • Landing gear installation and system adjustments
  • Emergency extension system adjustments

Navigation Systems (ATA 34)

  • Replacement and testing of Pitot/Static and AOA components
  • Software uploads and configuration verification

Oxygen System (ATA 35)

  • Leak tests after dismantling or component replacement

Pneumatic System (ATA 36)

  • Leak tests after repairs or replacements

Auxiliary Power Unit (ATA 49)

  • Leak tests in APU systems
  • APU replacement

Structures (ATA 51-57)

  • Repairs of primary structural elements, skin, and windows
  • Adjustments of door actuating mechanisms

Engines (ATA 70-83)

  • Engine replacement and component installations
  • Leak tests after assembly of fuel, oil, hydraulic systems
  • Adjustments and repairs to engine control systems

Next Steps

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Sofema Aviation Services (SAS) and Sofema Online (SOL) provide classroom, webinar and regulatory training in support of EASA Part 145 including CAT A critical task inspection – please see the websites or email team@sassofia.com

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Maintenance, avionics systems, flight control systems, Landing Gear Systems, Powerplant Installation, Emergency Systems, Propeller Systems, Air Conditioning (ATA 21), Auto Flight (ATA 22), Communications (ATA 23), Landing Gear (ATA 32), EASA Blogs