13.20 and 13.21 Integrated modular avionics (ATA 42) and cabin systems (ATA 44)

Scope

B2 level 3, not included in B2L ratings.

• 13.20 IMA: overall description and theory — core system and network components; typical layouts.
• 13.21 Cabin systems (ATA 44): in-flight entertainment; cabin intercommunication data system (CIDS); cabin–ground communication; flight attendant panels; the cabin network service (CNS) server and its interfaces (data/radio communication, cabin core system, IFES, external communication, cabin mass memory, cabin monitoring, miscellaneous cabin systems).

IMA concept

Integrated modular avionics replaces many dedicated "black boxes" (the federated architecture) with shared, standardised computing and network resources that host many applications.

Aspect	Federated	IMA
Processing	One computer per function	Shared core processing modules (CPM) in cabinets
Data exchange	Point-to-point (ARINC 429)	Switched network (AFDX / ARINC 664 part 7) plus RDCs
Spares	Many part numbers	Few common modules
Software	Tied to the box	Applications loaded into partitions
Weight/wiring	Higher	Lower

Core system

• CPM — processor, memory and network interface; runs a partitioned real-time operating system (ARINC 653 APEX interface).
• Robust partitioning: each hosted function gets time partitioning (fixed time windows in a repeating schedule) and space partitioning (protected memory). Functions of different criticality levels (DAL A to E) can safely share one module.
• I/O modules (IOM) and remote data concentrators (RDC)/common remote data concentrators (CRDC) convert analogue, discrete, ARINC 429 and CAN signals to network messages close to the sensors.
• Health monitoring and configuration management — the platform checks hardware and loaded software; mismatches generate maintenance messages.

Network components (AFDX)

• Based on full-duplex switched Ethernet with determinism added: virtual links (VLs) with guaranteed bandwidth (bandwidth allocation gap) and bounded latency.
• Two independent networks (A and B): every message is sent on both; the receiver keeps the first valid copy (redundancy management).
• Switches police traffic so a babbling end system cannot flood the network.
• End systems are the network interfaces in each subscriber.

Functions typically hosted (from the EASA list)

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

Typical layouts

Two or more IMA cabinets (left/right) in the avionics bay, dual AFDX networks with several switches, RDCs distributed through the fuselage and wings, displays and control panels as network subscribers, and legacy LRUs connected through gateways.

Maintenance points

• An LRM (line-replaceable module) is changed like an LRU but the software must be loaded and the configuration checked — "hardware OK, software wrong" is a real fault mode.
• Fault isolation uses the central maintenance system; troubleshooting the network needs AFDX-aware test tools.

Cabin systems (ATA 44)

CIDS — cabin intercommunication data system

• Directors (central computers) connected to cabin data buses (top-line/middle-line) with decoder/encoder units (DEUs) along the cabin.
• Functions: passenger address, cabin interphone, passenger call and lighted signs (no smoking, fasten seat belt, return to seat), cabin lighting control, emergency evacuation signalling, reading light control, lavatory smoke indication, water/waste quantity display, door/slide status, doors and drainmast heating status.
• Flight attendant panels (FAPs) — touch-screen control of lights, temperatures, water/waste servicing, PA/announcements, cabin configuration.
• Programming and test via the CIDS "cabin assignment module" or FAP; cabin layout changes are made by loading a new cabin configuration database.

In-flight entertainment (IFE/IFES)

• Head-end servers (audio/video on demand), seat electronic boxes, seat displays, passenger control units, area distribution boxes.
• Load shedding / IFE power cut-off switch — IFE must be de-energisable from the flight deck or cabin (non-essential load, smoke/fire procedure).
• Passenger connectivity: cabin Wi-Fi, mobile phone systems (pico-cell with network control unit to prevent interference with ground networks).

Cabin–ground communication (external communication system)

Voice, data, music and video transfer through SATCOM (Ku/Ka-band or L-band), air-to-ground cellular links or gatelink Wi-Fi.

Cabin network service (CNS)

A server-based network hosting cabin applications and interfacing with:

Interface	Role
Data/radio communication system	Link to aircraft radios/SATCOM
Cabin core system (CCS)	CIDS-type core functions
IFES	Entertainment
External communication system (ECS)	Off-board links
Cabin mass memory system (CMMS)	Storage for media and data
Cabin monitoring system (CMS)	Cameras/sensors, e.g. flight-deck door surveillance
Miscellaneous cabin systems	Other cabin equipment

Hosted functions may include access to pre-departure/departure reports, e-mail/intranet/internet for crew, and the passenger database (seat allocation, special requirements).