Avionics 101: Breaking Open Avionics ’ Complexity

Ken Elliott continues his Avionics 101 series by delving into the avionics categories, associated activities, and the systems themselves…

There are five core categories of avionics: Communication, Navigation, Surveillance, Interactive, and Cabin. When contemplating these categories remember that avionics are integrated and connect internally with the airframe and engines; with other aircraft operating in the vicinity; and with air traffic control.

Furthermore, the cabin occupants and the flight crew remain in contact with flight departments, corporations and others, in real time, during a trip.

Note that some cabin systems, such as Satcom, are shared by the cockpit, so there will often be a blurring between the five categories. Establishing the Avionics Activities

The above five categories have different avionics activities taking place within them. The central activities are as follows:

Communication

As time moves on, so do the methods, technology and infrastructure of the airspace system. The activities of avionics will continue to change and develop. Communication used to be voice-only, but that is fast transitioning to digital voice or data comm.

Communication used to be only aircraft-to-aircraft and aircraft-to-ground, but satellites have subsequently been launched allowing for satcom. Navigation

• Airport • En route

The same goes for Navigation, where different satellites enable predictable flight tracks to be flown, worldwide. The use of satellite GPS navigation reduces reliance on ground infrastructure. Originally, pilots navigated using combinations and variations of ADF, VOR, VLF/Omega, LORAN, DME, and INS (see Table B for Acronyms).

Now satellite-based GPS has been embraced, effectively only DME and INS are still widely used, while

VOR is slowly being phased out. Interestingly, DME has seen a revival, fueled largely by GPS cyber interference concerns, especially in a GPS-only environment.

Different technologies are required for the different avionics activities, and in some cases a single system is capable of more than one activity (as an example, a Flight Management System (FMS) copes with both en route and airport demands).

On the other hand, a typical Combined Vision System (CVS) is designed primarily for use in the vicinity of airports and not so much en route.

Surveillance

• Internal • External

Another benefit of avionics advancement is the ability of an aircraft to monitor itself. This relatively new activity is very different to the more familiar external surveillance of other aircraft using traffic, terrain, weather awareness, and emergency locating technologies.

Internal surveillance uses feedback sensing, and monitors aircraft data buses to collect, record, and report virtual live aircraft status information.

Interaction

• Control • Display • Annunciation

Pilots need to interact with aircraft and engine systems. They need to control and select functions, see display information, respond to annunciations and act on warnings. The ability to readily interact is made possible by greater integration of the different systems and subsystems.

For reasons of Size, Weight & Power, and cost (SWAPc), as well as increased reliability and safety, the integration of avionics has become more concentrated by developing a single card cage, covering multiple activities.

This method of gathering the different avionics systems in one assembly is known as Integrated Modular Avionics (IMA). This has replaced the traditional racks of avionics boxes found in most legacy aircraft. The concentration of data, processed in fewer Line Replacement Units (LRU), has transformed the behind-the-scenes look of the modern aircraft.

The same concentration has also permitted the display of more information in the cockpit. SWAPc considerations of how to handle the greater capabilities of cockpit displays has leveraged the commercial off-the-shelf (COTS) benefits of large-format flat screen displays, thus cleaning up the cockpit toward an ergonomic dream.

Cabin

• Comfort • Business • Entertainment

Nothing evolves faster than the features of an aircraft cabin. Partly, this is due to less regulation, and partly because the already advanced city-based office can easily become a business ‘ office in the sky ’ .

Cabin electronics have reaped the benefits of the commercial development of USB, HDMI, Wi-Fi, and Bluetooth, allowing the low energy transfer of data. The demand and popularity of walk-on devices; the desire for a ‘ wire free ’ seat experience; and even the luxury of a cappuccino machine, has made the cabin experience more like a trip to your local coffee shop.

Coupled with personal environmental and other comfort controls, today ’ s business aircraft traveler may take their business aloft, or relax with entertainment as they choose. 

What are the Systems?

Within each, and across multiple activities, are the various systems and their sub-systems. These are typically identified by their function, method or objective. The acronyms and terms, used for these, are familiar to many in the aviation community. Table A breaks out the systems under each of the four activities.

Some of the systems provide significant input to others, and can be considered as overlapping.

Following is an overview of the systems listed in Table A (right)…

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The communication systems mostly serve the different methods of voice and data, both to and from the aircraft. Radio operation is dependent on frequency bands that are best for different circumstances.

If flying regionally, airport to airport the frequencies are VHF and UHF (military). If operating in oceanic or remote areas, HF and Satcom/Iridium are necessary. Older Satcoms rely on Ku-band, Ka-band, as well as L-band to operate. Air-to-Ground (ATG) is domestic, mostly for non-Air Traffic communications, and is primarily used by the cabin. Examples of ATG are Gogo Business Aviation and SmartSky.

With voice being replaced by data-comm, VHF devices are now provided with both voice and data capability.

Cockpit internal crew communications and that between cockpit and cabin is controlled by two complex and very capable audio systems that are independent for each pilot. Navigation Systems As navigation has evolved, albeit slowly, we have moved from land and airport-based infrastructure to a combination of satellite- and aircraft-centric, standalone

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Surveillance Systems

External: It is only recently through transponder advancements that surveillance has come into its own. When you think about it, anything the aircraft does to watch, monitor and record is surveillance. So is the ability to alert others to any emergency.

Modern radars – as surveillance – are extremely 

capable, and are able to see weather, sense lightning, turbulence and windshear conditions.

Seeing other aircraft, terrain and obstacles is crucial to safety, so the aircraft surveils the sky and earth as an act of avoidance. The Transponders, ADS-B, TCAS, TAWS, SVS and EVS that are all used in navigation are crucial to this function, and are so smart they will provide only appropriate warnings and avoidance maneuvers in response to the aircraft’ s actual movement through the airspace.

The constant tracking of aircraft is becoming more acceptable and when Spaced-based ADS-B is fully implemented, the loss of an aircraft will occur less frequently. Even the pint-sized emergency ELT is now capable of sending position data, originating from the aircraft GPS.

Internal: Monitoring of onboard systems is also part of surveillance activity. Here, data is sensed, acquired, converted and processed to provide a virtual live status of aircraft and engine systems. The data can be stored in a MDAU, QAR, Combined Digital Flight Recorders (CVR/FDR), or it can be displayed to the crew and relayed to the ground via satellite data communications. This relatively new health monitoring of an aircraft is a burgeoning business. Interaction Systems

crew cockpit activity. Displays also now provide most of the annunciations and warnings that in former times were scattered (as separate annunciator blocks) throughout the instrument panel.

Both displays and controllers are becoming touchscreen capable. Knobs, cursors and buttons are replaced by direct on-screen selections. This, in turn, will remove separate controllers altogether as interactive activity can now take place on the cockpit displays.

When looking at business aircraft generally, you will see versions of displays and instruments that range from large format, flat panel touchscreens; to much-older cathode ray tube screens with separate analog instruments; and everything in between.

Anyone evaluating an aircraft trade, can safely assume that the greater the age of the aircraft, the more analog its functions and the more cluttered the cockpit will likely be.

Before data is displayed in the cockpit or used by other systems, it will be concentrated, adapted and enabled for transfer from side-to-side. Information may be displayed on multiple displays, some primary and some secondary. The more crucial the data is to the actual flight, the more it needs to be within the primary view of the pilots.

Because of redundancy and safety, all aircraft must have standby instruments. These are separately powered by an emergency battery and will permit the pilot flying (PF) to continue the flight to the nearest permissible runway, in the event of a total loss of aircraftgenerated power. 

Cabin Systems

The cabin is like an independent pod that sustains the needs of its passengers. Because today ’ s flyers desire a seamless experience between on-the-ground and in-theair, they can now board with their personal devices and connect the same way they would elsewhere.

Again, the three primary Cabin activities that the various onboard systems align with are:

1. Comfort - Environmental - Lighting - In-Seat Controls - Galley - Window Shades

2. Business - Satcom - Power and Data - Fax - Internet/Wi-Fi - News and Finance

3. Entertainment - Personal Devices - Stored Media - Live Satellite Media - Streaming Video - Air to Ground Internet - Iridium - In-seat and Bulkhead Displays

Avionics plays a role in all these systems and services. There is also significant overlap, where the same system can be offering resources that are useful for both business and entertainment purposes (i.e. onboard Wi-Fi).

Keep in mind that cabin comfort systems used to be analog-electrical in nature, using mechanical controls and electric devices, but because of the greater digitization of these features, today their support usually falls into the lap of the avionics specialist.

The cabin is controlled from the cockpit that enables its power, announces take-off and landings, and provides an intercom with a cabin call ability.

Larger business jets rely on a fully integrated CMS, where in-seat touchscreen controls and a galley panel will provide access to the cabin ’ s many features and functions. While the CMS has uniformity in all its devices, it does limit the operator when upgrades are required. More recently there have been situations where obsolescence of parts has required a complete CMS replacement, allowing third-party vendors to offer novel, and less expensive alternatives.

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In Summary

Avionics have expanded their portfolio over the past 100 years since the first communication devices and navigation instruments were introduced. Systems that control and direct the aircraft between airports have evolved to be more aircraft-centric, relying less on ground infrastructure, and sharing satellite data with other transport and technology.

With so many different aspects to avionics, it must be confusing to anyone new to aviation and even some veteran flyers. The hundreds of acronyms used throughout avionics (and other aircraft technologies) requires additional concentration from the enquirer.

Hopefully this foray into the surface layer of avionics will be helpful to AvBuyer readers. Future Avionics 101 articles will cover all five categories via separate articles, with a focus on information useful to owners, operators, consultants and brokers alike. ❙

KEN ELLIOTT

has 52 years of aviation experience focused on avionics in General and Business Aviation. Having a broad understanding after working in several countries on many aircraft types and avionics systems, he has contributed to several work groups and committees, including for NextGen, Airport Lighting, Human Factors, Unmanned Aircraft and Low Vision Technology. In retirement, he is striving to give back the knowledge gained with an eye on aviation’s future direction.

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