Module 11A.18–11A.21 — On-board maintenance systems, IMA, cabin systems and information systems

Levels and applicability

These four sub-modules apply only to turbine aeroplanes: A1 level 1, B1.1 level 2. They are not required for A2/B1.2 or B3. Each has a modest question allocation, but the terms are distinctive and easy marks if learned.

11.18 On-board maintenance systems (ATA 45)

Central maintenance computer (CMC / CMS / CFDS)

• Collects fault data from the BITE (built-in test equipment) of all connected LRUs, correlates them with flight-deck effects (warnings, cautions) and stores fault messages with ATA references, flight phase and time.
• Produces the post-flight report (PFR) and current-leg/previous-leg fault lists; supports ground tests, LRU identification (part and software numbers), and return-to-service tests.
• Accessed via the MCDU, a maintenance terminal, or a laptop/maintenance access terminal; data can be downlinked in real time via ACARS so engineers prepare before the aircraft arrives.
• Aircraft condition monitoring system (ACMS): records performance/engine trend data and parameters for reports (e.g. engine take-off reports), stored on a data management unit/QAR.

Data-loading system

• Loads field-loadable software (FLS) and databases (navigation database, configuration) into LRUs.
• Airborne data loader (ARINC 615) or portable data loader; network loading (ARINC 615A) on modern aircraft.
• Control: software part number configuration control per the IPC/AMM, loading from approved media, verification of the loaded part number and integrity (CRC) — cybersecurity and configuration control relevance (10.10).

Electronic library system

On-board electronic documentation — AMM, FCOM, MEL, wiring diagrams — available on maintenance terminals/EFB; revision control is essential.

Printing systems

Flight-deck printer (thermal) for ACARS messages, CMC reports, PFRs.

Structure monitoring (damage-tolerance monitoring)

• Structural health monitoring: sensors (strain gauges, comparative vacuum monitoring, acoustic emission, fibre-optic) monitor structural loads or crack growth in specific areas; flight load data used to adjust inspection intervals.
• Hard landing / overweight landing detection from accelerometer data triggers inspections.

11.19 Integrated Modular Avionics (ATA 42)

Concept

Traditional "federated" avionics use one dedicated box (LRU) per function. IMA hosts many functions as software applications on shared, standardised computing resources:

• Core processing modules (CPM) in cabinets or distributed — each runs multiple partitioned applications.
• Input/output modules (IOM) and remote data concentrators (RDC) convert analogue/discrete signals to network data near the sensors, reducing wiring.
• Network components: deterministic avionics Ethernet — AFDX (Avionics Full-Duplex Switched Ethernet, ARINC 664 part 7) with redundant A/B networks and switches; also ARINC 429 and CAN buses for legacy devices.
• Robust partitioning (ARINC 653): each application has guaranteed memory space and processing time so a fault in one cannot corrupt another — essential for certifying different criticality levels on one processor.

Functions typically integrated (syllabus list)

Bleed management, air pressure control, air ventilation and control, avionics and cockpit ventilation control, temperature control, air traffic communication, avionics communication router, electrical load management, circuit breaker monitoring, electrical system BITE, fuel management, braking control, steering control, landing gear extension and retraction, tyre pressure indication, oleo pressure indication, brake temperature monitoring, etc.

Typical system layout and maintenance implications

• Cabinets in the avionics bays connected via redundant switches to RDCs and displays.
• Faults are reported through the CMS; replacement of a module may require software loading and configuration (hardware part number + software part number).
• Benefits: lower weight, fewer spares types, easier upgrades. Drawbacks: complex fault isolation, configuration control, single module failures may affect several functions (mitigated by redundancy).

Key fact: IMA = shared computing modules with partitioned applications, linked by a deterministic network (e.g. AFDX/ARINC 664), with RDCs replacing much point-to-point wiring.