12.17–12.19 IMA, on-board maintenance and information systems (helicopters)

Scope

All three sub-modules are A level 1, B1.3 level 2 and together carry only a few questions — but the terminology is examined directly.

• 12.17 Integrated modular avionics (ATA 42): overall description and theory (functions that may be hosted, core system, network components) and typical layouts.
• 12.18 On-board maintenance systems (ATA 45): central maintenance computers, data loading, electronic library system.
• 12.19 Information systems (ATA 46): units that store, update and retrieve information formerly provided on paper, microfilm or microfiche.

From federated to integrated avionics

Federated architecture	Integrated modular avionics (IMA)
Each function has its own dedicated box (LRU) with its own processor, power supply and I/O	Many functions run as software applications on shared computing modules
Point-to-point wiring (e.g. ARINC 429)	Data shared over a network (e.g. AFDX/ARINC 664 Part 7, or CAN-type buses in smaller systems)
More weight, wiring and spares	Fewer box types, less weight and wiring, common spares
Change to one function affects one box	Software updates by data loading; changes need careful configuration control

IMA building blocks

• Core processing modules (CPMs) — general-purpose computers in a cabinet or rack.
• Partitioned operating system — each application runs in its own partition, protected in time (guaranteed processor time slots) and space (protected memory). A fault in one application cannot corrupt another. ARINC 653 is the common standard for this.
• I/O modules / remote data concentrators (RDCs) — convert analogue, discrete and legacy bus signals from sensors and actuators into network data, placed close to the equipment to shorten wiring.
• Network components — switches and redundant network planes (typically network A and B) so that the loss of one path does not lose data.
• Displays and control panels that subscribe to the data on the network.

Functions the EASA syllabus lists as candidates for IMA hosting: bleed management, air pressure control, ventilation and temperature control, air-traffic communication, avionics communication router, electrical load management, circuit-breaker monitoring, electrical BITE, fuel management, steering control, landing-gear extension/retraction, tyre-pressure and oleo-pressure indication, brake temperature monitoring.

Key fact: The defining feature of IMA is robust partitioning — several applications of different criticality share one processor without interfering with each other.

Maintenance implications:

• The hardware LRU may be serviceable while a software part number is wrong — configuration must be checked after any replacement.
• Fault isolation relies on BITE and the maintenance system rather than on substitution of boxes.
• Loading the wrong software is a maintenance error that the system checks (part-number and compatibility checks) but the engineer must confirm against the approved configuration.