Integrated Avionics: Plug & Play

The cursor control devices, pull-down menus and point-and-click controls in today’s bizjet cockpits remind us of PCs. Under the hood, in a corporate-owned airplane’s processing cabinets, the similarities persist, with integrated architectures that help make such intuitive features possible in real-time, flight critical environments.

The latest iterations of integrated avionics systems from Honeywell and Rockwell Collins begin to take processing to a "plug and play" level.

Honeywell, in its Primus Epic suite, perhaps has gone the furthest, allowing other manufacturers to plug utility avionics cards into the processing cabinet. In the corporate market, the Hawker Horizon will be the first to exploit this technique to the fullest, giving the new aircraft one of the most highly integrated bizjet avionics architectures.

"Robust partitioning" operating systems, used by all the major players, are a key technology driving integration. This software enables multiple applications–even at different criticality levels — to coexist on the same processing module. In one case, Honeywell located five functions on a generic processing module: air data monitoring, crew alerting, utility control, display control and configuration monitoring. And in a new cabinet currently fielded on U.S. Air Force KC-135s, Rockwell Collins can host civilian and military flight management applications on the same module. These operating systems also insulate software applications from the underlying hardware.

PC-Like Architecture

Because the hardware can be viewed separately from the software, Honeywell, for example, can offer generic, field-loadable modules that can be used on different aircraft, says Byron Birkedahl, senior technical staff engineer with Honeywell’s Business, Regional and General Aviation Division. The hardware modules are loaded only with "boot" software and data loading code. Loading software is even more convenient than with a PC, Birkedahl asserts. "All the executable software is contained on one CD."

At the simplest, physical level, PC "architectures" organize vital processing, input/output (I/O), memory, communication and control functions as cards (or chips on cards), which share data over a common bus, or backplane. When you need a new function, you plug in a new PC card or load a new software program from any vendor you choose. Empty slots are provided for system growth. And users can keep adding new applications and cards until they run out of processing and memory resources. PC cards also are automatically recognized and accepted by their parent computer.

PC owners can create an almost infinite variety of configurations, some of which will not work. If too many software applications simultaneously demand memory space and processor time, the system will slow down or crash. In a word, says Birkedahl, PCs are not "deterministic." The time to perform each task is not predetermined and guaranteed.

Avionics processing systems have to meet tough data integrity, availability, reliability and environmental requirements, to name just a few differences from PCs. But avionics designers nevertheless have recognized the advantages of integration. It makes sense to group associated functions together in a common enclosure, where they can share resources.

Fast interconnects and consolidation of functions as cards in a cabinet (or software on a card) also reduce latencies, compared with "federated," or dispersed, architectures, explains Stephen Brandt, senior director of aircraft systems and architectures with Rockwell Collins Commercial Systems. "When you do a point-and-click, you may be accessing several resident functions in the cabinet," he says. To be able to process the end results you want, you have to be able to `talk,’ or communicate, quickly." More sophisticated avionics systems locate modules on a shared backplane, using common interface circuitry.

In Honeywell’s case this common interface feature allows all cards to communicate over the backplane and ensures that they can be reused on other aircraft. Nevertheless, configurations have to be closely controlled. Cards are assigned specific slots in a cabinet and only predefined software applications can be installed in an aircraft. But aircraft type certificates often encompass multiple, separately tested configurations, giving the airframer a range of options for customers, such as single or dual implementations of hardware or software functions. Once a range of configurations has been proven and certified on a certain airplane, however, it is pretty much set until upgrades are developed and, in turn, certified.

Shedding Weight

Honeywell’s Primus Epic cabinet processes data for about 14 utility functions. Utilities provided by other manufacturers can be implemented as third-party modules in the cabinet. Honeywell integrates other utilities in software only, residing on generic processor cards. This substitution of software programming for stand-alone boxes helps save 300 to 400 pounds (136 to 181 kg). Engineers can eliminate line replaceable units, with their associated connectors and wiring, control panels and mechanical switches, says Doug Endrud, Honeywell’s technical manager, Primus Epic utility integration.

The consolidation of much utilities processing in the cabinet also will allow designers to produce more intuitive synoptic displays. "You’d run your cursor over to the valve pictured on the screen, make your changes right on the screen, and see them happen," Endrud explains.

Today Primus Epic can integrate — in software on generic processing cards — utilities functions such as hydraulic control/monitoring, ice/rain protection control/monitoring, oxygen control/monitoring, bleed air control/monitoring, fire protection monitoring, and thrust reverser control/monitoring. The Hawker Horizon and Embraer 170 use this technique to varying degrees. Honeywell envisions ultimately converting utility cards into protected, proprietary software programs running on processor cards.

Will integration ever reach a point of diminishing returns? "You’re probably only limited by your I/O capability and the physical segregation requirements driven by the certification process," Brandt opines. As long as processors are fast enough to handle the loads and buses are speedy enough to move the data where it needs to go, integration will continue to enhance performance. And higher levels of integration ideally will allow designers to continue to reduce size, weight and power requirements, "all of which are `golden’ when it comes to the economics of aircraft operation."

Honeywell also uses aircraft-wide, "dual/ dual" redundant avionics standard communication buses (ASCBs) between aircraft systems. (There are four separate ASCB cables running through the aircraft–two mirror copies on the "pilot" side and two on the "copilot" side. Data also is shared between the two sides.) ASCB, moreover, is like a protocol, explains Tom Hilpert, Raytheon’s director of product development for Hawker Horizon. The anti-skid braking control system, for example, packaged as a module on the backplane, sends out certain data "words" simultaneously onto the ASCB buses.

Chinese Regional Jet

The most recent version of the Collins cabinet is planned for the ARJ21 Chinese regional jet, slated for certification in 2008. This architecture employs 10/100-Mbit/s Ethernet technology as both the backplane bus and the aircraft avionics network. Honeywell also will provide the ARJ21’s fly-by-wire (FBW) system, combining small, stand-alone analog computers and cabinet-based "augmentation" processing. The latter will be implemented in a pair of small, single-purpose Primus Epic cabinets.

Collins’ integrated processing system (IPS)–the cabinet plus modules–is a dual-channel unit, where flight-critical data resides on the Ethernet only. The Ethernet backplane provides a "hub and spoke" architecture. A digital switching module acts as the hub while generic processing nodes form the spokes. The end result, according to Collins, is a high-speed, flexible and deterministic data network.

The Collins system was delivered to the U.S. Air Force last year, as part of an upgrade to the KC-135 tanker fleet. The core cabinet also will be integrated as part of the U.S. Navy P-3 Orion and International C-130 upgrades.

The IPS can include generic "common computing modules," data switching modules, power and environmental modules, as well as more specialized display processing and "unique interface" modules.

Collins also has added an external file server unit (FSU), which manages database information for applications such as Jeppesen navigation charts and online weather. The FSU supports 2 to 16 Gbytes of data and includes an Ethernet portal for fast software loading.

Honeywell’s stand-alone data management unit (DMU) serves as a data loader unit for avionics software applications and as a file server for Jeppesen charts and maps. But it is not Honeywell’s "general platform for file serving," Birkedahl emphasizes. File serving for advanced displays such as terrain data, obstacles, navigation data and uplinked weather are located in cabinet-based modules.

In the future, Collins will offer the FSU as a module, as well. "For the ARJ21 we’re provisioning the ability to have a file server module," Brandt says. So regional and business aviation customers will be able to decide whether to have file server functions inside or outside the cabinet. The company also may host the ARJ21’s FMS and "a large part of the autopilot" on a single module. Display processing, moreover, can be handled in the cabinet rather than at the displays. On the Boeing 7E7, for instance, Collins will provide a display processing module.

Hawker Horizon

Primus Epic on the Hawker Horizon, "super mid-sized" business jet takes integration to new heights in corporate aviation. The system is "very similar to what goes on in a PC," says Raytheon’s Hilpert. "Honeywell defines the interface and [other manufacturers’] develop cards, meeting that interface requirement, to integrate into that Honeywell cabinet." Pilots address aircraft systems through a multifunction control display unit and via point-and-click actions on the 8-by-10-inch displays. These interfaces allow pilots to select system modes, monitor system status and select or de-select "virtual" circuit breakers for virtually all aircraft systems.

Hawker Horizon incorporates the following utility avionics modules:

• Landing gear control module, by Eldec;

• Anti-skid brake control system, by Aircraft Braking Systems Co.;

• Nose wheel steering, by Messier-Dowty;

• Fuel control and computation, by Smiths Aerospace (only on Hawker); and

• Engine vibration system, by Vibro-meter.

The engine vibration system module also is used in the Embraer 170/190 and Gulfstream G450 and G350.

Primus Epic employs a backplane bus and four separate aircraft system buses. The virtual backplane PCI (VbPCI), a Honeywell implementation based on PCI, allows deterministic performance. Cards "talk" over the backplane and out of the cabinet, across the aircraft system buses.

A module’s data is transmitted simultaneously over multiple ASCB buses, so every module has access to essentially all avionics data. Says Raytheon’s Hilpert, "There are always multiple paths. We are carrying all of the signals between the cabinets and any of the displays — and the active systems like the nose wheel steering — on [at least] two paths simultaneously."

The redundant paths allow you always to complete your mission, he adds. The Hawker employs two dual-channel cabinets, with duplication of critical functions within each cabinet, such as power supplies and brake control modules. The VbPCI backplane provides a throughput of 800 Mbits/s and the ASCBs offer a combined 20 Mbits/s.

Modules can talk on the backplane because they incorporate a backplane interface connection (BIC) circuit, explains Endrud. The BIC, like a small memory circuit, allows the network interface controller (NIC) module to pull data from the cards and post it to the cards over the backplane.

To avoid traffic jams on the backplane, Primus Epic synchronizes communications so that only one module talks at a time. Like a traffic cop, the NIC pushes data to the cards and pulls data from the cards in predefined sequences.

Primus Epic also provides a 10-Mbit/s Ethernet local area network (LAN), which connects a high-speed data loader unit, printer, maintenance computer and every NIC in the system. The LAN is used for data loading, DMU file access, central maintenance computer data transfers, ground maintenance terminal data access and printing.

Pro Line’s Evolution

The first big step toward avionics integration in business aviation was Rockwell Collins’ Pro Line 4 avionics suite, the company claims. Development began in the early 1980s for Raytheon’s Starship. Honeywell, however, likes to point out that its SPZ-6000/8000 system, certified in the mid-1980s, used the initial version of its avionics standard communications bus (ASCB). Honeywell’s Primus 2000, first certified in the early 1990s, centered around an "integrated line-replaceable unit," including autopilot, flight management system, electronic flight instrument system and radio control functions. The Primus 2000 today is used on the Cessna Citation X, among other aircraft.

Collins changed its integrated processing architecture’s name from Pro Line 4 to Pro Line 21 in the mid-1990s to mark the move to higher-performance liquid crystal displays (LCDs), recalls Bruce Thigpen, the company’s senior director of marketing for business and regional systems. The bulk of the LCD display processing in both Pro Line 4 and Pro Line 21 is handled by embedded processing in the display system–"smart displays."

Pro Line 4 and the early Pro Line 21 systems implement Collins’ integrated avionics processing system (IAPS) architecture, which groups a few avionics functions, such as autopilot, flight management computer and I/O concentration, in a single cabinet. "We put all the boxes that had to talk together in the same place," Thigpen explains. IAPS modules use common power supplies, environmental protection and cooling. While there is no common bus for modules to talk with each other, the cabinet employs a number of ARINC 429 links to communicate with other aircraft systems.

After finishing the development of the integrated processing system (IPS) cabinet now on U.S. Air Force KC-135s, Collins expanded the Pro Line 21 architecture to bring electronic charts and enhanced graphics to aftermarket and forward-fit aircraft. This package, known as the Integrated Flight Information System (IFIS), does not require the IPS and its Ethernet backplane, says Stephen Brandt, Rockwell Collins’ senior director of aircraft systems and architectures. For IFIS you need:

• An external file server unit (FSU) to manage and pull data from charting and other databases;

• A 10/100-Mbits/s Ethernet link between the FSU and the displays; and

• A display upgrade to add Ethernet interfaces.

The FSU can host third-party applications such as XM Radio’s or Universal Weather’s graphical weather software and Jeppesen’s electronic chart database. Other functions, such as processing for an electronic flight bag, also could be folded into the 2-MCU box, says David Wu, director of marketing for flight deck systems.

Collins has certified IFIS on the company’s Challenger CL601. It also has certified a "dual IFIS" system, which will allow the company to offer a truly paperless cockpit. When an aircraft is equipped with dual displays and dual IFS, the system provides the necessary data availability (through redundancy) to remove paper data, such as maps and charts, from the aircraft.

Current & Expected Certifications of Integrated Avionics Suites