Avionics
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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.
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.
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[edit] 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 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.
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.
[edit] Design constraints
Any equipment fitted to aircraft has to meet a series of rigorous design constraints. The aircraft presents electronics with a unique and sometimes highly complex environment.
Airworthiness and certification is one of the most costly, time consuming, troublesome and difficult aspects of building any aircraft. As aircraft and aircrew reliance on avionics has increased, it has placed a heavy duty of responsibility on the robustness of these systems. One necessary factor of constructing avionics systems is that a flight control system must be designed so that it never fails. However, degrees of this level of robustness can be found in every system fitted to aircraft.
[edit] Integration
The means of connecting the vast array of systems together such that the information can be used in a cohesive and useful fashion have vexed the avionics industry from the start. The simplicity of a discrete wire telling a device that something is either on or off has grown all the way to the incorporation of fibre optic data buses moving flight control data around the aircraft. Ever more complex software has been written to ever more rigorous standards.
Integration of systems into aircraft is one of the largest problems for engineers today. However small the aircraft, there is always some level of integration (whether or not it operates with the aircraft power supply, for example). The large aircraft projects (military and civilian alike) employ hundreds of engineers to integrate these complex systems.
[edit] Physical environment
The environment for any aircraft is different. Systems have many uses. Some need to be more robust than others. Today all avionics systems go through some level of environmental testing. This allows design authorities the ability to be assured of the robustness of the design.
The testing comes in many forms, and has for many aircraft been pre-ordained by airframe manufacturers. As avionics became more ubiquitous on all sorts of aircraft, the Airworthiness Authorities (e.g. UK CAA or US FAA) set performance standards which equipment should meet. The manufacturers grew this to standards that define the environmental standards that the equipment should meet.
These standards place upon the avionics manufacturers predefined methods and agreed levels of testing for aircraft parts. Things such as salt spray, waterproofness, mould growth, and effects of external contamination and so on are all tested for.
Standards such as BS 3G 100, MIL-STD-810, DEF STAN 00-35 have all been written to provide manufacturers with these methods. Each individual test is assessed as to its usefulness on the item (e.g. salt spray tests may not need to be done on equipment housed inside sealed bays). Manufacturers maintain standards by cross referencing these standards and level of testing required; often generating top level general requirements. These do not dictate performance, but are an expression of the environment which the equipment must operate within.
[edit] Electromagnetic compatibility (EMC)
Also known as EEE, EMC is an engineering activity that assesses the effect of one electrical electronic system on another. In the world of aircraft, EMC can cause all sort of problems, and equipments and aircraft are extensively tested using specific standards (Def Stan 59-41, MIL-STD-464 etc.).
[edit] Vibration
For even the most benign of aircraft (like an airliner), vibration is a serious issue as it has major impacts on reliability. On more aggressive aircraft like helicopters, vibration can be the major driver in the design. There are aircraft standards available for vibration, but many airframes do not recognise them. Vibration resonances will be different for almost every aircraft built, but they are certainly different for every type.
[edit] System safety
All parts of the aircraft are subject to regular system safety analyses. In avionics, methods for analysing the safety impacts of a system are dictated by airworthiness authorities of the individual nation. Invariably methods like one managed by the FAA or EASA (JAA) will be used for civilian aircraft. In the military world, whilst there are some world wide standards, lots of military purchasing authorities will dictate local standards (like Def Stan 00-56).
The safety methodologies will significantly impact the design in terms of reliability and usage. Any system using software will be subject to even more scrutiny with respect to its safety impact.
[edit] Quality
The procurement of avionics equipment is all part of a worldwide assortment of manufacturers. Whilst highly recognisable manufacturers will provide the parts for the 'insides' of a box or LRU (Line-replaceable unit), the specialist element of packaging, testing and managing the configuration of avionics falls into the domain of a few big players.
Quality control of parts is a significant part of any major industry, but in avionics and aviation as a whole, supplier quality can break entire programmes (see the Boeing Chinook problems). Quality procedures dictated by ISO 9001 are now the starting blocks for any major business. However, all the main airframers have their own highly stringent quality procedures for delivery of documentation and hardware. It is often said that aircraft fly not on fuel, but on paperwork, since a single LRU (a radio or instrument) can produce excessive documentation.
[edit] 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.
[edit] 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.
[edit] 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
[edit] 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.
[edit] 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 within the last 5 years. 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.
[edit] 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.
[edit] 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, aircraft use systems such as ground-proximity warning systems (GPWS), often combined with a radar altimeter. Newer systems use GPS combined with terrain and obstacle databases to provide similar alerting for light aircraft.
[edit] 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 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.
[edit] 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 centralised 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.
[edit] 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.
[edit] 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.).
[edit] 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. While the civil market has had weather radar for a while, there are strict rules about using it to navigate the aircraft.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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
- AFDX: Specific implementation of ARINC 664(AND) 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
- MIL-STD-1553: Military Aircraft
- Time-Triggered Protocol (TTP): For Distributed Hard Realtime Control Applications in Airbus A380, Boeing 787, F-16, ...
[edit] 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.
