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Most of today’s collision-avoidance, in-flight-entertainment (IFE), air-to-ground-communications, and other avionics systems employ electronics packaging based on the Aeronautics Radio INC (ARINC) 600 standard. Compared to the older ARINC 404 standard dating from the 1970s that defined “black box” enclosures and racks within aircraft, ARINC 600 specified a Modular Concept Unit (MCU) – the basic building block module for avionics. An ARINC 600 metal enclosure can hold up to 12 MCUs, allowing a lot of computing power to be placed in a centralized “box.” By making it possible to run numerous applications over a real-time network, ARINC 600 enabled “next generation” integrated modular avionics (IMA).

A centralized IMA approach offers several advantages: reduced size and weight, easier maintenance with standardized cards that are easily replaceable, and expanded data transmission speed and bandwidth. However, a centralized big box has some significant limitations, which inspired the development of ARINC 800 series standards at the turn of this century.

ARINC 800 standards respond to the general technological trend toward embedded computing on miniaturized printed circuit boards (PCBs) deployed locally. This trend got started in other industries looking for ways to reduce weight and size, handle higher data loads due to the proliferation of sensors, improve thermal management, and push intelligence closer to the point where control decisions are made. For example, automotive designers now employ a myriad of electronic control units (ECU) in highly engineered cars, and consumer product designers embed numerous intelligent controls in “connected” consumer appliances.

This trend is now moving into avionics. Embedded computing and distributed architecture are combining to push IMA to the next level. Designers can now implement modular and distributed avionics throughout the aircraft using miniaturized electronics packaging to perform navigation, communications, the gathering of various sensor information, and other intelligent functions locally without being wired back to a central microcomputer.

To this end, a family of new ARINC 800 standards was developed, which include:

  • ARINC 801 through 807 that advance the use of fiber optics in avionics systems;

  • ARINC 836 that defines modular, standardized rack-style enclosures, cabling, connectors, and grounding methods for aircraft cabins;

  • ARINC 836A that updates the original ARINC 836 standard to establish a mini modular rack principle (MiniMRP) for avionics packaging. (Initially aimed at commercial cabin systems, ARINC 836A MiniMRP is also finding use in military aerospace.)

New latching mechanisms for TE’s MiniMRP enclosure (courtesy of TE Connectivity)

For the designer, ARINC 836A MiniMRP makes it possible to realize the full potential of integrated modular and distributed avionics. The basic technical goal of ARINC 836A was to define standardized cabin-system-module form factors for weights ranging from a few ounces to a maximum of six pounds.

The advantages of MiniMRP implemented in TE Connectivity (TE) technologies include:

  • Significantly reduced size with a 40% smaller package and up to 60% weight savings;

  • Enhancing flexibility and simplifying configuration with a less costly commercial-off-the-shelf (COTS) selection approach;

  • Securing modules and boards with robust latches and interconnects;

  • Increasing network speed and bandwidth by supporting 10-Gigabit Ethernet over fiber optics and/or high-speed copper, with a fiber optic backbone that can support 40G and even 100G links.

By using miniaturized, standardized modules that can be mixed and matched within a high-speed network, designers enjoy far greater design flexibility in avionics placement and cabling than with centralized architectures. It's worth examining how TE’s MiniMRP delivers these design advantages.

Smaller, Lighter

ARINC 836A MiniMRP modules are available in four compact size combinations: single-width (42 mm/1.6 inches) or double-width (84 mm/3.3 inches), and single-height (112.3 mm/4.4 inches) or double-height (224.8 mm/8.8 inches) variations. Lightweight composite materials replace traditional heavy metal enclosures. Advanced composite formulations — including base materials and fillers — can be selected according to specific application needs. Fillers range from carbon fibers to microsphere and nanotubes. Composites can be selectively plated to add shielding, circuit elements, and other features, such as embedded antennas. Sometimes considered an expensive, exotic solution, composite enclosures are now more cost-effective thanks to advanced manufacturing techniques.

Flexibility and Configuration

With MiniMRP avionics, a big box in the avionics bay can be replaced with many small boxes distributed throughout the aircraft. Modules can be used singly or combined as needed for specific functionality and external environmental factors. MiniMRP packaging encompasses connecting hardware, including bus-structured modules, interfaces, and power supplies. Standardization allows designers to take advantage of COTS components to lower costs and speed up the design cycle. Modules are designed for quick and easy tool-less installation. Changes, maintenance, and upgrades can be accomplished by simply swapping out modules.

Robust Latches and Interconnects

Avionics designers often face tight constraints with PCBs; design flexibility is accounted for by using European Standard EN4165-mateable interconnects for modular racks. With a fully-integrated MiniMRP design, PCB connector modules and boxes can be securely latched using techniques to protect against pull-out and torsion. The preferred connector for MiniMRP modules is the classic DEUTSCH DMC-M series aircraft connector. This design conforms to demanding avionics specifications, including EN4165. The DMC-M family offers many contact arrangements and insert layouts in both multi-cavity and singlemodule configurations. Sizes include 8, 12, 16, 20, and 22 gauges. Contacts can be crimped on copper wire, aluminum wire, or PCB mounting.