Chapter 19: Maintenance, IMA, Cabin and Information Systems

On-board maintenance systems (ATA 45)

Central maintenance computers and BITE

• Built-in test equipment (BITE) in every digital LRU checks itself: power-up BITE when switched on, continuous BITE in operation, and initiated BITE (tests started by the engineer). Results are stored in the LRU's non-volatile memory and reported over the data buses.
• The central maintenance computer (CMC) — CFDS on the A320, CMCS on Boeing types, OMS on the A350/A380 — collects these reports, correlates each crew alert (flight-deck effect) with the fault messages that caused it, identifies the most likely failed LRU, and stores everything by flight leg (current-leg and previous-legs reports, fault history).
• The engineer uses it through the MCDU or a maintenance terminal to read reports, run ground tests and system tests, see configuration reports (part and software numbers of each LRU), and load software.
• Faults and reports are sent in real time via ACARS to the airline's maintenance control (aircraft health monitoring), so spares and engineers can meet the aircraft. An aircraft condition monitoring system (ACMS) records engine and system trends and exceedances, often with a quick-access recorder.

Data loading, electronic library and printing

• Data loading system — field-loadable software and databases (FMS navigation database, terrain database, LRU software) are loaded with a portable or airborne data loader (ARINC 615) or over the aircraft network (ARINC 615A); the software parts follow the ARINC 665 standard. After loading, the software part number is checked and recorded — loading the wrong or unapproved software is a configuration error just like fitting the wrong part.
• Electronic library system — the manuals and charts the crew need, held electronically (often on the EFB or an on-board server) instead of on paper.
• Printing systems — a flight-deck printer for ACARS messages, maintenance reports and weather; sometimes cabin printers.

Structure monitoring (damage-tolerance monitoring)

• Load and event monitoring — accelerometers and gear data detect hard or overweight landings, severe turbulence and exceedances and generate a report (e.g. a LOAD report) that triggers the AMM conditional inspection.
• Usage monitoring — counting flight cycles, hours and loads accurately, supporting the inspection thresholds and intervals of the damage-tolerance programme (Chapter 3).
• Structural health monitoring (SHM) sensors — strain gauges, acoustic-emission sensors, comparative vacuum monitoring (CVM) sensors bonded over known crack sites, and fibre-optic sensors — can detect cracks or impact damage in hard-to-reach areas without dismantling, and are increasingly approved to replace some scheduled inspections.

Integrated modular avionics (ATA 42)

• Federated avionics give every function its own LRU with its own processor, power supply and I/O, connected point-to-point (ARINC 429). Simple to certify, but heavy, with many spares and miles of wiring.
• Integrated modular avionics (IMA) runs many functions as hosted applications on shared core processing modules (for example CPIOMs on the A380/A350, general processing modules of the B787 common core system). I/O modules or remote data concentrators near the sensors and actuators convert their signals onto the network.
• Robust partitioning (time and memory, under an ARINC 653 operating system) ensures one application cannot disturb another on the same module — essential when functions of different criticality share hardware.
• Benefits: fewer, standardised boxes, less wiring and weight, common spares, and changes made largely in software. Maintenance becomes module replacement followed by software and configuration loading, with fault isolation from the maintenance computer.
• Typical hosted functions: bleed and cabin-pressure control, ventilation and temperature control (including avionics and cockpit ventilation), fuel management and quantity, braking and steering control, landing-gear extension/retraction monitoring, tyre-pressure, oleo-pressure and brake-temperature monitoring, electrical load management and electronic circuit-breaker monitoring, electrical system BITE, and communication routing (air-traffic and avionics communication routers).

Cabin systems (ATA 44)

• Cabin intercommunication data system (CIDS) (Airbus; Boeing uses a cabin services system) — directors with decoder/encoder units (DEUs) along the cabin carry passenger address, cabin and flight interphone, passenger and crew calls, cabin lighting, signs (seat belt, no smoking, exit), evacuation signalling, lavatory smoke, door/slide status and water/waste indication. Its configuration (cabin layout, zones) is held in a programmable memory and changed when the cabin layout changes.
• Flight attendant panels (FAPs) — touch screens where cabin crew control lights, temperatures, announcements, water/waste information, IFE and see door and system status.
• In-flight entertainment (IFE) — head-end servers, seat electronics boxes, seat-back screens and passenger controls, or wireless streaming to passengers' devices; seat power outlets. A master IFE / cabin power switch lets the crew remove power for smoke or electrical problems.
• Cabin–ground communication — SATCOM (or air-to-ground) links carry voice, data, music and video for passengers and crew.
• Cabin network server (CNS) — hosts cabin network applications and interfaces: data and radio communication, the cabin core system, the IFE system, the external communication system, the cabin mass memory, the cabin monitoring (CCTV) system and miscellaneous cabin systems; and functions such as pre-departure/departure reports, e-mail and intranet/internet access for crew, and the passenger database.
• Data are exchanged between the cabin LRUs over cabin data buses and Ethernet.

Information systems (ATA 46)

• Information systems store, update and retrieve the digital information that replaces paper on board: manuals, charts, logbooks, performance data, maintenance documentation and fault data.
• Network server systems (and on some types air-traffic and information management systems) host the electronic library, applications and the links to the ground — by gate-link Wi-Fi or cellular, or in flight by SATCOM.
• Flight-deck information system — the EFB (portable or installed) with charts, performance calculation, electronic manuals and checklists.
• Maintenance information system — the electronic technical log, maintenance documentation, fault data from the CMC and data loading, often through a maintenance laptop or on-board terminal.
• Passenger cabin information system — cabin logbook, passenger information and connectivity; plus miscellaneous and other linked systems.
• Updating databases and software, with strict configuration control; retrieving information on screens and printers.
• Security: systems are grouped into domains of decreasing criticality — aircraft control, airline information services, passenger information and entertainment, passenger-owned devices — with firewalls and one-way gateways between them. Protecting the aircraft from cyber threats is now part of continuing airworthiness.