The Eclipse 500's innovative Avio avionics and systems management suite is a key element of the personal jet

The first flight of Vern Raburn's Eclipse 500 personal jet not only marks the birth of a new, potentially paradigm-shifting force in the general aviation market, it also sees the first use of a sophisticated integrated avionics and systems management suite, called Avio.

 The makers of Avio make lofty claims for the system, developed specifically for the Eclipse 500. Not only is it thought to be the most integrated suite ever to fly in a business or general aviation aircraft, Eclipse also believes it offers more functionality within one system than even that of the relatively recent Boeing 777. Company president and chief executive Vern Raburn describes Avio as one of the three defining "legs" of the project, along with two other technological breakthroughs - the Williams International EJ22 turbofan and large-scale manufacturing based on friction-stir welding.

The Avio system makes the Eclipse 500 "the most electronic and computerised aircraft the general aviation industry has seen. We can't think of any other civil aircraft that comes close. The only examples are in the military world - the [Bell Boeing] V-22 and [Lockheed Martin/Boeing] F-22, that's the level of integration we've talking about", Raburn says.

Avio emerged from Eclipse's driving requirements for increased safety, reliability and functionality while at the same time reducing cost and weight.

Although these targets rarely intersect, the Avio team's ability to start from scratch with a clean sheet design was a big help, says Raburn. "It was designed from the ground up and is driven far more by computer technology than aircraft technology."

Given the Eclipse project's unusual nature and its over-arching target to be the most affordable personal jet ever built, Raburn says taking hold of the avionics and systems design from the start was key. "We decided a long time ago [1999] to take on the role of system integrator. That's a job usually done by a major avionics company. This is where the name Avio comes from: it is about turning the aircraft into an intelligent 'whole'. A lot of our guys in this area are not out of the aviation industry because there aren't many in the general aviation industry who can really do this."

Eclipse created Avio with Avidyne, BAE Systems, General Dynamics (GD) and Williams International. "Avidyne played a big role in the initial architecture, BAE and GD contributed mostly in the control area and Williams on power control software," says Raburn. The charter of the system is simple: Avio has to "know" what the aircraft is doing, it must integrate environmental data and calculate the correct action. It must communicate with the pilot and assist in managing the aircraft. The architecture was guided by an emphasis on safety through redundancy and extensive built-in testing, as well as a focus on easing pilot workload through high levels of integration. Another guiding principle was intrinsic use of modern databus communications and data switching. The system connects via 13 databuses (ARINC 429 and RS-422), and seven "Byteflight" connection pathways.

Benign environment

The "brains" of Avio reside chiefly in two BAE-developed aircraft integrated electronics units (AIEUs), while other "lobes" include the electric power distribution system (EPDS) and the avionics and pilot information and control components. The AIEU controls the engines, housing full authority digital engine control (FADEC) channels on cards slotted PC-like into the mother board of the processor. Unlike virtually all other FADECs, the digital engine control is therefore housed in the relatively benign environment of the AIEU inside the aircraft pressure vessel, rather than the far harsher regime of the nacelle. In all, the aircraft has 30 modules containing software of which 17 are inside the pressure vessel. Four FADEC cards are installed, any of which can run the engine by itself.

The AIEUs, either of which can run the aircraft, also host the aircraft computer system. This, in turn, runs sensor systems, such as fuel level, secondary engine sensors and in the environmental control system (ECS). Autopilot, auto-throttle, yaw damper and roll boost functions also live in the unit, as does the control of systems such as flaps, landing gear, external lighting and ECS. 

The EPDS houses its own fault-detection software, as well as current and voltage monitors. The system makes widespread use of electronic circuit breakers (ECBs), which provide higher reliability, and which have "tighter tolerances during operations, mainly due to their electronic sensing capability", says Don Taylor, vice-president safety and operations. One microprocessor is dedicated to sensing current for each breaker, with a total of 120 on the power system. The plan is to go to 100% ECBs, "though we still have three mechanical circuit breakers left", adds Taylor. The ECBs can also be used as electronic switches as well as breakers. They monitor output voltage and current and therefore play a part in health reporting. Once tripped, they require pilot intervention to be reset.

Other major components include the Avio-driven primary flight displays (PFDs) and centrally mounted, large format multi-function display (MFD). There are noelectro-mechanical back-up instruments and, with US Federal Aviation Administration approval, the back-up displays are also electronic and projected on a section of either the PFD or MFD. The 26cm (10in) liquid-crystal PFDs are split horizontally, with the upper screen showing flight management system (FMS) mode annunciation, airspeed (with trend vector), vertical speed and instrument landing system. The lower screen shows the horizontal situation (HSI), lateral navigation and active route moving map display. It also depicts weather radar information as well as the location of nearby airports, a flightpath predictor, navigation source indicator and a list of radio frequencies.

The broader (35cm wide) MFD can be used as an alternate PFD if needed, but is normally used for FMS mode display and flight-planning data, back-up instruments (airspeed, attitude and altitude), digital maps, synoptics such as fuel reporting and electrical system control, engine parameters and "paperless" cockpit features.

This includes checklists that are automatically presented when required or requested. "When you start turning the aircraft systems on, it knows you are about to go flying so it will automatically show the pre-start checklist and so on," says Raburn.

Synoptic displays

The system control and synoptic displays cover fuel, electrical, ECS/pressurisation, electronic circuit breakers, flaps and speedbrakes as well as landing gear. Navigation and communication features include dual VHF communication/navigation, localiser and glideslope, Mode S transponder, global positioning system and attitude and heading reference system with air data computer. Operationally, the Avio system will be capable of supporting reduced vertical separation minima.

Other than the standard glareshield mounted flight guidance and autopilot functions, pilot interface with Avio is conducted through a cursor control (for use with the MFD) and keyboard mounted at the base of the instrument panel. The keyboard is arranged in alphabetical order, rather than the traditional QWERTY, after human factors recommendations from the US Air Force. "We are still developing the keyboard," says Taylor, who adds that the "overriding result is that you have a minimum two ways of doing everything".

The result is a remarkably clean, uncluttered cockpit layout up front and, behind the scenes, an "order of magnitude reduction in the number of boxes, two orders of magnitude reduction in cost and at least one order of magnitude reduction in weight", says Raburn. "You couldn't get this functionality for much less than $1 million if you went to the original equipment manufacturers," he adds.

Tests of the initial avionics and electrical system will begin in earnest in December when the fourth test airframe, aircraft 103, enters the certification programme. Further tests will also be undertaken by the first and second "Beta" airframes, aircraft numbers 106 and 107 which are both due to join the test programme in March. The key test for Avio perhaps, might not be technical, but financial. Its unprecedented functionality is both a a cost saver and, potentially if problems arise, a cost drain. With Eclipse so fundamentally driven by cost as a whole, the success of the entire programme may therefore depend on the performance and acceptance of Avio.

Source: Flight International