avionics

 

(ā'vēŏn'ĭks) , electronic instruments used in air or space flight; also the design and production of such instruments. Early planes had few instruments, but as aviation and aircraft became more complex, so did instrumentation. Most of the new technology was electronic; hence, the expression “aviation electronics” arose and was later shortened to “avionics.” After World War II, the increasing sophistication of military avionics helped spawn a proliferation of electronic applications to commercial and private aviation. Avionics includes numerous types of devices, including those used for navigation (see air navigation); control instruments that aid in steering and controlling the craft; and performance indicators, such as altimeters and velocity gauges.

Avionics is a portmanteau which literally means aviation electronics. In essence it comprises all electronic systems designed for use on an aircraft. At a basic level this comprises communications, navigation and the display and management of multiple systems. It also comprises the literally hundreds of systems that are fitted to aircraft to meet individual roles. These can be as simple as a search light for a police helicopter or as complicated as the tactical system for an Airborne Early Warning platform. Avionics also refers to the electronics on artificial satellites and spacecraft.

The study of avionics and its impact on aerospace technology has grown at an amazing rate. Initially the ancillary part of an aircraft, avionics has, for many aircraft, become the sole reason for its existence. Increasingly, military aircraft become the means of placing powerful and sensitive sensors into a tactical environment.

History

The term avionics did not gain any credence or general use until the early 1970s. Up to this point instruments, radios, radar, fuel systems, engine controls and radio navigation aids had all formed individual and often mechanical systems.

In the 1970s avionics was born. Driven by changes in the electronics industry as a whole, the avionics market boomed. However, where once aircraft and space flight set the standard, it was not long before the rest of the industry was in control. In the early 1970s military aircraft consumed 90% of the world’s semiconductor production. By the mid 1990s it was less than 1%. Airframers started to bring together its specialists. They formed Avionics Departments and by the end of the 1970s a whole new segment of the aviation industry had been formed.

This was mostly driven by military need rather than civil airliner development (the cold war). A large number of aircraft had become flying sensors platforms, and making large amounts of electronic equipment work together had become the new challenge. Today, avionics as used in military aircraft almost always forms the biggest part of any development budget. Aircraft like the F-15E and the now retired F-14 have roughly 80% of their budget spent on avionics. Most modern helicopters now have budget splits of 60/40 in favour of avionics. (F-22?)

The civilian market has also seen a massive growth in cost of avionics. Flight control systems (fly-by-wire) and new navigation needs brought on by tighter airspaces, have pushed up development costs accordingly. The major change has been the recent boom in consumer flying. As more people begin to use planes as their primary method of transportation, more elaborate methods of controlling aircraft safely in these high restrictive airspaces have been invented. Whilst the nature of civil aircraft means that avionics is almost always confined to the cockpit, the budgets and development made in the civil market has for the first time started to influence the military.

Main categories

Avionics, like electronics, is a massive subject that does not easily lend itself to simple categorisation. The headings below try to allocate areas of interest, from which you can delve deeper into the subject areas.

Aircraft avionics

The cockpit of any aircraft is the most obvious location for avionics. It is also the most contentious and difficult. Systems that allow the aircraft to fly safely or have direct control over the aircraft are all directly controlled by the pilot. These safety critical systems and the items that support them are all referred to as aircraft avionics.

Communications

Probably the first piece of avionics to exist, the ability to communicate from the aircraft to the ground has been crucial to aircraft design since its inception. The boom in telecommunications has meant aircraft (civilian and military) fly with a vast array of communication devices. A small number of these provide the critical air to ground communications systems for safe passage. On board communications are provided by public address systems and aircraft intercoms.

The VHF aviation communication system works on the Airband of 118.000 MHz to 136.975 MHz. Each channel is spaced from the adjacent by 8.33 kHz. Amplitude Modulation AM is used. The conversation is performed by simplex mode.

See also: Aircraft Communication Addressing and Reporting System

Navigation

This article concerns navigation in the sense of determination of position and direction on or above the surface of the Earth.

Soon after communications the envelope within which an aircraft could be operated was limited by the conditions. Navigation sensors have been developed from the early days to assist pilots in safe flight. As with communications, there is a vast array of radio navigation and relative aircraft based navigation devices that can be fitted to an aircraft. One of the most important ways in which aircraft navigation is done today is with the aid of the GPS system.

Displays

The advent of avionics as a separate entity was quickly followed by integration of these functions. The drive to manufacture more reliable and better quality means of displaying flight critical information to pilots started very early on. True glass cockpits have only started to come into being since the G-IV in 1985. The introduction of LCD or CRT displays was often backed up by conventional instruments.

Today the reliability of LCDs means that even these flight critical back ups are 'glass'. But this is only the superficial element. Display systems carry out checks of key sensor data that allows the aircraft to fly safely in very aggressive environments. Display software is often written in the same way as that for flight control software, as essentially the pilot will follow it. The display systems can take multiple different methods of determining attitude, heading and altitude that the aircraft use, and provide them in a safe and easy to use manner to aircrew.

Aircraft flight control systems

Main article: Aircraft flight control systems

Aeroplanes and helicopters have had different means of automatically controlling flight for many years. They reduce pilot workload at useful times (like on landing, or in the hover), and they make these actions safer by 'removing' pilot error. The first simple auto-pilots were used to control heading and altitude and had limited authority on things like thrust and flight control surfaces. In helicopters, auto stabilisation was used in a similar way. The old systems were all electromechanical in nature until very recently.

The software driven systems fitted to almost all new major aircraft today have made a significant leap forward. The advent of fly by wire and electro actuated flight surfaces (rather than the traditional hydraulic) has massively increased safety. As with displays and instruments, critical devices which were electro-mechanical had a finite life which was very restrictive. Electronic systems are not limited by the mechanical constraints. With safety critical systems, the software is written in very strict conditions, where the ideal scenario is that it will never fail.

Collision-avoidance systems

To supplement air traffic control, most large transport aircraft and many smaller ones use a TCAS (Traffic Alert and Collision Avoidance System), which can detect the location of other, nearby aircraft, and provide instructions for avoiding a midair collision. Smaller aircraft may use simpler traffic alerting systems such as TPAS, which are passive (they do not actively interrogate the transponders of other aircraft) and do not provide advisories for conflict resolution.

To help avoid collision with terrain, (CFIT) aircraft use systems such as ground-proximity warning systems (GPWS), radar altimeter being the key element in GPWS. Newer systems (EGPWS) use GPS combined with a terrain and obstacle databases to provide more warning time.

Weather systems

Weather systems such as weather radar (typically Arinc 708 on commercial aircraft) and lightning detectors are especially important for aircraft flying at night or in Instrument meteorological conditions, where it is not possible for pilots to see the weather ahead. Heavy precipitation (as sensed by radar) or severe turbulence (as sensed by lightning activity) are both indications of strong convective activity and severe turbulence, and weather systems allow pilots to deviate around these areas.

Recently, there have been three important changes in cockpit weather systems. First, the systems (especially lightning detectors like the Stormscope or Strikefinder) have become inexpensive enough that they are practical for light aircraft. Second, in addition to the traditional radar and lightning detection, observations and extended radar pictures (such as NEXRAD) are now available through satellite data connections, allowing pilots to see weather conditions far beyond the range of their own in-flight systems. Finally, modern displays allow weather information to be integrated with moving maps, terrain, traffic, etc. onto a single screen, greatly simplifying navigation.

Aircraft management Systems

As integration became the buzzword of the day in avionics, and as PCs came onto the market, there was a natural progression towards centralized control of the multiple complex systems fitted to aircraft. Combined with displays and flight control systems, these three core systems allow all the aircraft systems (not just avionics) to have their data compiled and manipulated to make it easier to maintain, easier to fly and safer.

Engine monitoring and management was an early progression into aircraft management for ground maintenance. Now the ultimate extension of this is total management of all the components on the aircraft, giving them longer lives (and reducing cost). Health and Usage Monitoring Systems (HUMS) are integrated with aircraft management computers to allow maintainers early warnings of parts that will need replacement.

The aircraft management computer or flight management systems are used by aircrew in place of reams of maps and complex equations. Combined with the digital flight bag they can manage every aspect of the aircraft chock to chock.

Although avionic manufacturers provide flight management systems, aircraft management and HUMS tend to be specific to the airframe as the design of the software is dependent on the aircraft it is fitted to.

Mission or tactical avionics

The major developments in avionics have tended to happen 'in the back' before the cockpit. Military aircraft have been designed either to deliver a weapon or to be the eyes and ears of other weapon systems. The vast array of sensors available to the military (as for the front) is then used for whatever tactical means required. As with aircraft management, the bigger sensor platforms (like the E-3D, JSTARS, ASTOR, Nimrod MRA4, Merlin HM Mk 1) have mission management computers.

As the sophistication of military sensors increases and they become more ubiquitous, the pseudo-military market has started to dip into the product. Police and EMS aircraft can now carry some very sophisticated tactical sensors.

Military communications

While aircraft communications provide the backbone for safe flight, the tactical systems are designed to withstand the rigours of the battle field. UHF, VHF Tactical (30-88 MHz) and SatCom systems combined with ECCM methods, and cryptography secure the communications. Data links like Link 11, 16, 22 and BOWMAN, JTRS and even TETRA provide the means of transmitting data (such as images, targeting information etc.).

Radar

Airborne radar was one of the first tactical sensors. As with its ground based counterpart it has grown in sophistication. The obvious massive benefit of altitude providing massive range has meant a significant focus of developing airborne radar technologies. The general ranges of radar of Airborne Early Warning (AEW), Anti-Submarine Warfare (ASW), and even Weather radar (Arinc 708) and ground tracking/proximity radar.

The military has used radar in fast jets to help pilots fly at low levels in several operations. While the civil market has had weather radar for a while, there are strict rules about using it to navigate the aircraft.

Sonar

Soon after radar came sonar. Dipping sonar fitted to a range of military helicopters allows the helicopter to protect shipping assets from submarines or surface threats. Maritime support aircraft can drop active and passive sonar devices (Sonobuoys) and these are also used to determine the location of hostile submarines.

Electro-Optics

Electro-optic system covers a wide range of systems, including Forward Looking Infrared (FLIR), and Passive Infrared Devices (PIDS). These are all used to provide imagery to crews. This imagery is used for everything from Search and Rescue through to acquiring better resolution on a target.

ESM/DAS

Electronic support measures and defensive aids are used extensively to gather information about threats or possible threats. Ultimately they can be used to launch devices (in some cases automatically) to counter direct threats against the aircraft. They are also used to determine the state of a threat or even identify it.

Aircraft Networks

The avionics systems in military, commercial and advanced models of civilian aircraft are interconnected using an avionics databus. These network protocols are similar in functionality as an in-home network connecting computers together, however, the communication and electrical protocols can be very different. Here is a short list of some of the more common avionics databus protocols with their primary application:

• Aircraft Data Network (ADN): Ethernet derrivative for Commercial Aircraft
• Avionics Full-Duplex Switched Ethernet (AFDX): Specific implementation of ARINC 664 (ADN) for Commercial Aircraft
• ARINC 429: Commercial Aircraft
• ARINC 664: See ADN above
• ARINC 629: Commercial Aircraft (Boeing 777)
• ARINC 708: Weather Radar for Commercial Aircraft
• ARINC 717: Flight Data Recorder for Commercial Aircraft
• IEEE 1394b: Military Aircraft
• MIL-STD-1553: Military Aircraft
• MIL-STD-1760: Military Aircraft

Police and Air Ambulance

Police and EMS aircraft (mostly helicopters) are now a significant market. Military aircraft are often now built with a role available to assist in civil disobedience. Police helicopters are almost always fitted with video/FLIR systems to allow them to track suspects or items they or their command are interested in. They can also be fitted with searchlights and loudspeakers for the very same reason police cars are.

EMS helicopters obviously need medical equipment, which is rarely classified as avionics. However, many EMS and Police helicopters will be required to fly in unpleasant conditions, this may require more aircraft sensors, some of which were until recently considered purely for military aircraft.

External links

• Space Shuttle Avionics
• Aviation Today Avionics magazine
• RAES Avionics homepage

See also

• Flight data recorder (FDR)
• Emergency locator transmitter (ELT)
• Integrated Modular Avionics
• Avionics software
• ARINC

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