4.3 Facilities, Tools, Equipment, Maintenance Data & Procedures

Facility Requirements and Storage Segregation (145.A.25)

Under 145.A.25, an approved maintenance organisation must provide facilities appropriate for all planned maintenance work. The standard requires that the physical working environment actively protects aeronautical components and technicians from physical degradation, environmental contamination, and industrial hazards.

Environmental Protection and Working Bays

• Hangar Infrastructure: Working bays and hangars must be of sufficient volume and physical dimensions to fully house the aircraft types listed on the organisation's scope of approval.
• Weather Protection: Facilities must provide complete isolation from prevailing weather conditions, including rain, snow, hail, high winds, and airborne dust. If environmental conditions (e.g., extreme humidity, sub-zero temperatures, or airborne sand) degrade materials or human performance, work must be suspended.
• Specialised Workshop Segregation: Workshops and working bays must be segregated to prevent cross-contamination. Critical operations—such as composite laminating cleanrooms, aircraft paint stripping and spraying booths, battery charging rooms, engine teardown bays, and welding shops—must be physically walled off and equipped with dedicated ventilation and air-handling units.

Storage Conditions and Stores Segregation (145.A.25(d))

Storage facilities for serviceable aircraft parts, raw materials, and tooling must satisfy rigorous environmental and security requirements:

1. Secure Bonded Stores: Access must be strictly restricted to authorized stores personnel. Serviceable parts must be stored in manufacturer-recommended packaging under climate-controlled conditions (temperature and humidity) to prevent corrosion, condensation, or elastomer deterioration.
2. Quarantine Store: The organisation must operate a physically segregated, clearly designated, and securely locked quarantine holding area. This facility is exclusively reserved for unserviceable components, unidentifiable parts, cannibalized items awaiting documentation, and Suspected Unapproved Parts (SUP), preventing their accidental fitment to aircraft.
3. Shelf-Life and Expiry Control: Consumables and materials subject to time degradation (e.g., sealants, adhesives, pre-impregnated carbon fabrics, elastomeric O-rings, paints, escape slide squibs) must be managed under a strict First-In, First-Out (FIFO) protocol. Expiry dates must be tracked electronically, and expired goods tagged and discarded immediately.
4. Electrostatic Discharge (ESD) Precautions: Sensitive avionics line replaceable units (LRUs) containing semiconductor components must be stored in conductive antistatic bags. ESD workstations must feature grounded dissipative mats, wrist straps, and periodic ground-integrity monitoring.

---

Tooling, Equipment, and Calibration Traceability (145.A.40)

Under 145.A.40, the organisation must possess all necessary tooling, equipment, and test apparatus required to perform the maintenance tasks defined within its approved scope of work. Tooling control is governed by two complementary requirements: availability and measurement accuracy.

Tool Availability and Equivalency Procedures

• Tools and equipment specified in the applicable maintenance data (e.g., the AMM or CMM) must be directly available on site during maintenance.
• Where an alternative tool is used in place of the OEM-specified tool, the organisation must establish an approved Tooling Equivalency Procedure in MOE Part 2.4. An engineering evaluation must prove that the alternative tool satisfies or exceeds the dimensional, electrical, or structural tolerances defined by the Type Certificate holder.

Calibration Register and National Measurement Standards

All inspection, measuring, and test equipment (IMTE) whose accuracy affects airworthiness—such as torque wrenches, pressure gauges, tensiometers, micrometers, multimeters, flow meters, and pitot-static test sets—must be controlled under a formal Calibration Programme:

• Serialisation and Register: Every tool requiring calibration must have a unique serial number and be recorded in a centralized Calibration Control Register.
• Traceability: Calibration must be performed at defined statutory intervals against working standards that possess verified traceability to national or international metrology standards (such as NIST, PTB, NPL, or ISO/IEC 17025 accredited laboratories).
• Status Labeling: Each calibrated tool must bear a secure calibration label displaying the serial number, date of last calibration, calibration agency, and exact recalibration due date.
• Out-of-Tolerance Protocol: If a tool is dropped, damaged, or found out of calibration during routine checks, it must be withdrawn from service and quarantined immediately. Crucially, the organisation must investigate and document whether any aircraft or component released using that tool since its last valid calibration was rendered unairworthy.

Tool Control and Foreign Object Debris (FOD) Prevention

To prevent tooling from being left inside aircraft structures or engines—a major cause of catastrophic accidents—organisations must enforce rigorous tool control policies:

• Standardized shadow boards and dual-color foam cutouts in technician toolboxes;
• Laser-etched or barcode-tracked hand tools;
• Electronic tool check-in/check-out kiosks;
• Mandatory tool audits before closing access panels and before issuing a Certificate of Release to Service (CRS);
• Technicians using personal hand tools must have them registered, shadowed, and controlled under the company's approved tool management system.

---

Maintenance Data Control and Hierarchy (145.A.45)

Under 145.A.45, the maintenance organisation must hold and use applicable, current maintenance data when planning and performing maintenance. Using obsolete or unapproved technical data is a direct violation of European continuing airworthiness law.

Applicable Maintenance Data Scope

Applicable maintenance data is formally defined as:

1. Any applicable requirement, regulation, or order issued by the Competent Authority or EASA (e.g., EASA CS, Part-145, Part-M);
2. Any applicable Airworthiness Directive (AD) issued by EASA or adopted from the State of Design;
3. Instructions for Continuing Airworthiness (ICA) issued by the Type Certificate (TC) holder, Supplemental Type Certificate (STC) holder, or Part-21 design approval holder. These include the Aircraft Maintenance Manual (AMM), Component Maintenance Manual (CMM), Structural Repair Manual (SRM), Illustrated Parts Catalogue (IPC), Wiring Diagram Manual (WDM), Fault Isolation Manual (FIM), and Service Bulletins (SB/ASB);
4. Approved repair data and modification data approved under EASA Part-21;
5. The customer's approved Aircraft Maintenance Programme (AMP).

Maintenance Data Revision and Control Procedures

The organisation must subscribe to revision services from manufacturers and regulatory agencies to ensure data is updated promptly. Digital technical libraries must have version control safeguards ensuring that technicians cannot access superseded revisions. Work cards and job instruction sheets must display the exact manual revision status and date.

Modification of Maintenance Instructions (145.A.45(d))

A critical legal principle governs technician conduct: Maintenance personnel are strictly forbidden from modifying OEM maintenance instructions on their own initiative.

• Transcribing OEM data into company job cards is permissible under MOE Part 2.13, provided the technical instructions and engineering tolerances are copied without alteration.
• If an error, ambiguity, or physical impossibility is discovered in OEM data, the technician cannot invent an ad-hoc local work-around. The organisation must record the discrepancy, notify the Type Certificate holder, and seek a formal revision or an approved engineering concession (such as an approved Part-21 repair design) before releasing the work.

---

Production Planning and Maintenance Procedures (145.A.47 & 145.A.48)

Maintenance execution is governed by two complementary operational articles: 145.A.47 (Production Planning) and 145.A.48 (Performance of Maintenance).

Production Planning System (145.A.47)

The organisation must maintain a structured production planning system that coordinates maintenance work packages. The system must verify that all necessary:

• Hangar bays, dockings, and environmental facilities;
• Approved current maintenance data and job cards;
• Required parts, consumables, and raw materials;
• Calibrated tooling and specialized ground support equipment; and
• Appropriately qualified certifying staff and support staff; are physically available and confirmed before maintenance commences, preventing the disruption of partially completed aircraft.

Shift Handover Protocols (145.A.48(a))

Communication breakdowns during shift handovers represent one of the most prolific failure vectors in aviation maintenance history (exemplified by the Aloha Airlines Flight 243 and Continental Express Flight 2574 accidents). Under 145.A.48(a) and AMC 145.A.48(a), organisations must mandate a formal Shift Handover Protocol:

• Documented Handover Logs: Outgoing personnel must record all partially completed tasks, open defects, missing parts, tool locations, and specific safety lockouts in written or electronic handover logs.
• Verbal Briefing: Outgoing and incoming supervisors and certifying staff must conduct a structured, face-to-face verbal debriefing.
• Physical Inspection: Where complex mechanical or flight-critical systems are disturbed, the handover must include a joint physical walk-around to verify the actual state of the aircraft.

Error-Capturing Methods and Critical Maintenance Tasks (145.A.48(b))

To prevent single human errors from causing catastrophic accidents, Part-145 mandates specific error-capturing procedures for Critical Maintenance Tasks:

Definition of Critical Maintenance Tasks

A critical maintenance task is any task that involves the assembly, disturbance, or rigging of an aircraft system where a single error—if undetected—could directly result in a catastrophic aircraft failure, loss of control, or structural collapse. Examples include:

• Assembly, rigging, or adjustment of primary and secondary flight controls (ailerons, elevators, rudder, flaps, spoilers);
• Engine control linkages, throttle cables, and Full Authority Digital Engine Control (FADEC) harness connections;
• Propeller pitch mechanisms and thrust reverser actuation systems;
• High-pressure hydraulic flight control actuators and landing gear extension/retraction mechanisms;
• Dual engine oil servicing, magnetic chip detector installation, or fuel filter replacements.

Minimization of Multiple Errors (Common-Cause Failure)

Under 145.A.48(b), the organisation must plan maintenance to minimize the risk of multiple errors on identical or redundant systems. EASA strictly prohibits having the same individual perform identical critical maintenance tasks on both engines of a multi-engine aircraft, or across multiple redundant flight control hydraulic circuits, during the same maintenance check.

Independent Inspection (Secondary Inspection) Protocol

For any critical maintenance task, the organisation must perform an Independent Inspection:

1. Task Execution: The primary maintenance task is completed and signed off by the executing technician.
2. The Independent Inspector: An authorized person who did not participate in performing the maintenance task conducts the independent inspection.
3. Inspection Scope: The independent inspector physically verifies:
   • Correct assembly, alignment, and orientation of all components;
   • Correct sense of operation (e.g., control column backward deflection produces elevator up deflection);
   • Full range of movement without binding, fouling, or excessive friction;
   • Installation and locking of all fasteners, split pins, lockwire, tab washers, and torque-seal indicators.
4. Re-Inspection Protocol: If an aircraft system subjected to independent inspection is subsequently disturbed, adjusted, or disconnected prior to flight, the entire critical task and the independent inspection must be performed and recorded again.

---

Practical Maintenance Scenario & Module 10 Exam Tips

Maintenance Practical Scenario: During scheduled line maintenance on a twin-engine Airbus A320, the oil filters on both CFM56 engines are scheduled for replacement. Under 145.A.48(b), the organisation cannot assign a single technician to replace the oil filters and torque the filter housing bowls on both engines during the same shift. Doing so creates a common-cause failure risk (e.g., mis-seating both O-rings). Two different technicians must perform the task on Engine 1 and Engine 2, or if performed sequentially by one technician, an independent inspection must be carried out by a separate authorized person on both engines to verify correct seating, torque, and locking.

Module 10 Exam Tips:

• Quarantine stores must be physically segregated and locked; unserviceable or unapproved parts cannot be kept on open shelves.
• Calibrated tools must have traceability to national or international measurement standards (NIST, PTB, NPL, ISO 17025).
• Technicians cannot modify OEM maintenance instructions; unauthorized deviations or ad-hoc work-arounds are strictly illegal under 145.A.45.
• Critical maintenance tasks require an independent inspection performed by an authorized person who did not participate in the task.
• If a system is disturbed after an independent inspection, the entire critical task and independent inspection must be repeated.