Avionics

Radar and other avionics in the nose of aCessna Citation I/SP

F-105 Thunderchiefwith avionics laid out

Avionics(ablendofaviationandelectronics) are theelectronicsystems used onaircraft.Avionic systems include communications,navigation,the display and management of multiple systems, and the hundreds of systems that are fitted to aircraft to perform individual functions. These can be as simple as asearchlightfor apolice helicopteror as complicated as the tactical system for anairborne early warningplatform.

History

The term "avionics"was coined in 1949 byPhilip J. Klass,senior editor atAviation Week & Space Technologymagazine as aportmanteauof "aviation electronics".

Radio communicationwas first used in aircraft just prior toWorld War I.The firstairborneradios were inzeppelins,but the military sparked development of light radio sets that could be carried by heavier-than-air craft, so thataerial reconnaissancebiplanes could report their observations immediately in case they were shot down. The first experimental radio transmission from an airplane was conducted by theU.S. Navyin August 1910. The first aircraft radios transmitted byradiotelegraphy,so they required two-seat aircraft with a second crewman to tap on atelegraph keyto spell out messages byMorse code.During World War I,AMvoicetwo way radiosets were made possible in 1917 by the development of thetriodevacuum tube,which were simple enough that the pilot in a single seat aircraft could use it while flying.

Radar,the central technology used today in aircraft navigation andair traffic control,was developed by several nations, mainly in secret, as anair defensesystem in the 1930s during the runup toWorld War II.Many modern avionics have their origins in World War II wartime developments. For example,autopilotsystems that are commonplace today began as specialized systems to help bomber planes fly steadily enough to hit precision targets from high altitudes.Britain's 1940 decision to share its radar technology with its U.S. ally, particularly themagnetronvacuum tube,in the famousTizard Mission,significantly shortened the war.Modern avionics is a substantial portion of military aircraft spending. Aircraft like theF-15Eand the now retiredF-14have roughly 20 percent of their budget spent on avionics. Most modernhelicoptersnow have budget splits of 60/40 in favour of avionics.

The civilian market has also seen a 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. 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.

Modern avionics

Avionics plays a heavy role in modernization initiatives like theFederal Aviation Administration's (FAA)Next Generation Air Transportation Systemproject in the United States and theSingle European Sky ATM Research(SESAR) initiative in Europe. TheJoint Planning and Development Officeput forth a roadmap for avionics in six areas:

• Published Routes and Procedures – Improved navigation and routing
• Negotiated Trajectories – Adding data communications to create preferred routes dynamically
• Delegated Separation – Enhanced situational awareness in the air and on the ground
• LowVisibility/CeilingApproach/Departure – Allowing operations with weather constraints with less ground infrastructure
• Surface Operations – To increase safety in approach and departure
• ATM Efficiencies – Improving theair traffic management(ATM) process

Market

TheAircraft Electronics Associationreports $1.73 billion avionics sales for the first three quarters of 2017 inbusinessandgeneral aviation,a 4.1% yearly improvement: 73.5% came from North America, forward-fit represented 42.3% while 57.7% wereretrofitsas the U.S. deadline of January 1, 2020 for mandatoryADS-Bout approach.

Aircraft avionics

The cockpit or, in larger aircraft, under the cockpit of an aircraft or in a movable nosecone, is a typical location foravionic bayequipment, including control, monitoring, communication, navigation, weather, and anti-collision systems. The majority of aircraft power their avionics using 14- or 28‑voltDCelectrical systems; however, larger, more sophisticated aircraft (such asairlinersor military combat aircraft) haveACsystems operating at 115 volts 400 Hz, AC.There are several major vendors of flight avionics, includingThe Boeing Company,Panasonic Avionics Corporation,Honeywell(which now ownsBendix/King),Universal Avionics Systems Corporation,Rockwell Collins(now Collins Aerospace),Thales Group,GE Aviation Systems,Garmin,Raytheon,Parker Hannifin,UTC Aerospace Systems(now Collins Aerospace),Selex ES(nowLeonardo), Shadin Avionics, andAvidyne Corporation.

International standards for avionics equipment are prepared by the Airlines Electronic Engineering Committee (AEEC) and published by ARINC.

Communications

Communications connect the flight deck to the ground and the flight deck to the passengers. On‑board communications are provided by public-address systems and aircraft intercoms.

The VHF aviation communication system works on theairbandof 118.000 MHz to 136.975 MHz. Each channel is spaced from the adjacent ones by 8.33 kHz in Europe, 25 kHz elsewhere. VHF is also used for line of sight communication such as aircraft-to-aircraft and aircraft-to-ATC.Amplitude modulation(AM) is used, and the conversation is performed insimplexmode. Aircraft communication can also take place using HF (especially for trans-oceanic flights) or satellite communication.

See also:Aircraft Communication Addressing and Reporting System

Navigation

Main article:Air navigation

Air navigationis the determination of position and direction on or above the surface of the Earth. Avionics can usesatellite navigationsystems (such asGPSandWAAS),inertial navigation system(INS), ground-basedradio navigationsystems (such asVORorLORAN), or any combination thereof. Some navigation systems such as GPS calculate the position automatically and display it to the flight crew on moving map displays. Older ground-based Navigation systems such as VOR or LORAN requires a pilot or navigator to plot the intersection of signals on a paper map to determine an aircraft's location; modern systems calculate the position automatically and display it to the flight crew on moving map displays.

Monitoring

Main article:Glass cockpit

TheAirbus A380glass cockpit featuring pull-out keyboards and two wide computer screens on the sides for pilots

The first hints ofglass cockpitsemerged in the 1970s when flight-worthycathode ray tube(CRT) screens began to replace electromechanical displays, gauges and instruments. A "glass" cockpit refers to the use of computer monitors instead of gauges and other analog displays. Aircraft were getting progressively more displays, dials and information dashboards that eventually competed for space and pilot attention. In the 1970s, the average aircraft had more than 100 cockpit instruments and controls. Glass cockpits started to come into being with theGulfstreamG‑IV private jet in 1985. One of the key challenges in glass cockpits is to balance how much control is automated and how much the pilot should do manually. Generally they try to automate flight operations while keeping the pilot constantly informed.

Aircraft flight-control system

Main article:Aircraft flight control system

Aircraft have means of automatically controlling flight.Autopilotwas first invented byLawrence SperryduringWorld War Ito fly bomber planes steady enough to hit accurate targets from 25,000 feet. When it was first adopted by theU.S. military,aHoneywellengineer sat in the back seat with bolt cutters to disconnect the autopilot in case of emergency. Nowadays most commercial planes are equipped with aircraft flight control systems in order to reduce pilot error and workload at landing or takeoff.

The first simple commercial auto-pilots were used to controlheadingand altitude and had limited authority on things likethrustandflight controlsurfaces. Inhelicopters,auto-stabilization was used in a similar way. The first systems were electromechanical. The advent offly-by-wireand electro-actuated flight surfaces (rather than the traditional hydraulic) has increased safety. As with displays and instruments, critical devices that were electro-mechanical had a finite life. With safety critical systems, the software is very strictly tested.

Fuel Systems

Fuel Quantity Indication System (FQIS) monitors the amount of fuel aboard. Using various sensors, such as capacitance tubes, temperature sensors, densitometers & level sensors, the FQIS computer calculates the mass of fuel remaining on board.

Fuel Control and Monitoring System (FCMS) reports fuel remaining on board in a similar manner, but, by controlling pumps & valves, also manages fuel transfers around various tanks.

• Refuelling control to upload to a certain total mass of fuel and distribute it automatically.
• Transfers during flight to the tanks that feed the engines. E.G. from fuselage to wing tanks
• Centre of gravity control transfers from the tail (trim) tanks forward to the wings as fuel is expended
• Maintaining fuel in the wing tips (to alleviate wing bending due to lift in flight) & transferring to the main tanks after landing
• Controlling fuel jettison during an emergency to reduce the aircraft weight.

Collision-avoidance systems

Main article:Aircraft collision avoidance systems

To supplementair traffic control,most large transport aircraft and many smaller ones use atraffic alert and collision avoidance system(TCAS), which can detect the location of 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 thetranspondersof other aircraft) and do not provide advisories for conflict resolution.

To help avoid controlled flight into terrain (CFIT), aircraft use systems such asground-proximity warning systems(GPWS), which use radar altimeters as a key element. One of the major weaknesses of GPWS is the lack of "look-ahead" information, because it only provides altitude above terrain "look-down". In order to overcome this weakness, modern aircraft use a terrain awareness warning system (TAWS).

Flight recorders

Main article:Flight recorder

Commercial aircraft cockpit data recorders, commonly known as "black boxes", store flight information and audio from thecockpit.They are often recovered from an aircraft after a crash to determine control settings and other parameters during the incident.

Weather systems

Main articles:Weather radarandLightning detector

Weather systems such asweather radar(typicallyArinc 708on commercial aircraft) andlightning detectorsare important for aircraft flying at night or ininstrument meteorological conditions,where it is not possible for pilots to see the weather ahead. Heavy precipitation (as sensed by radar) or severeturbulence(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.

Lightning detectors like the Stormscope or Strikefinder have become inexpensive enough that they are practical for light aircraft. In addition to radar and lightning detection, observations and extended radar pictures (such asNEXRAD) are now available through satellite data connections, allowing pilots to see weather conditions far beyond the range of their own in-flight systems. Modern displays allow weather information to be integrated with moving maps, terrain, and traffic onto a single screen, greatly simplifying navigation.

Modern weather systems also includewind shearand turbulence detection and terrain and traffic warning systems.In‑plane weather avionics are especially popular inAfrica,India,and other countries where air-travel is a growing market, but ground support is not as well developed.

Aircraft management systems

There has been a progression towards centralized control of the multiple complex systems fitted to aircraft, including engine monitoring and management.Health and usage monitoring systems(HUMS) are integrated with aircraft management computers to give maintainers early warnings of parts that will need replacement.

Theintegrated modular avionicsconcept proposes an integrated architecture with application software portable across an assembly of common hardware modules. It has been used infourth generation jet fightersand the latest generation ofairliners.

Mission or tactical avionics

Military aircrafthave 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 is 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.

Police and EMS aircraft also carry sophisticated tactical sensors.

Military communications

While aircraft communications provide the backbone for safe flight, the tactical systems are designed to withstand the rigors of the battle field.UHF,VHFTactical (30–88 MHz) and SatCom systems combined withECCMmethods, andcryptographysecure the communications. Data links such asLink 11,16,22andBOWMAN,JTRSand evenTETRAprovide the means of transmitting data (such as images, targeting information etc.).

Radar

Airborneradarwas one of the first tactical sensors. The benefit of altitude providing range has meant a significant focus on airborne radar technologies. Radars includeairborne early warning(AEW),anti-submarine warfare(ASW), and evenweather radar(Arinc 708) and ground tracking/proximity radar.

The military usesradar 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.

Sonar

Dipping sonar fitted to a range of military helicopters allows thehelicopterto 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 enemy submarines.

Electro-optics

Electro-optic systems include devices such as thehead-up display(HUD),forward looking infrared(FLIR),infrared search and trackand other passive infrared devices (Passive infrared sensor). These are all used to provide imagery and information to the flight crew. This imagery is used for everything from search and rescue tonavigational aidsandtarget acquisition.

ESM/DAS

Electronic support measures and defensive aids systems are used extensively to gather information about threats or possible threats. 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 and identify it.

Aircraft networks

The avionics systems in military, commercial and advanced models of civilian aircraft are interconnected using an avionics databus. Common avionics databus protocols, with their primary application, include:

• Aircraft Data Network(ADN): Ethernet derivative for Commercial Aircraft
• Avionics Full-Duplex Switched Ethernet(AFDX): Specific implementation of ARINC 664 (ADN) for Commercial Aircraft
• ARINC 429:Generic Medium-Speed Data Sharing for Private and 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
• ARINC 825:CAN busfor commercial aircraft (for exampleBoeing 787andAirbus A350)
• Commercial Standard Digital Bus
• IEEE 1394b:Military Aircraft
• MIL-STD-1553:Military Aircraft
• MIL-STD-1760:Military Aircraft
• TTP– Time-Triggered Protocol:Boeing 787,Airbus A380,Fly-By-Wire Actuation Platforms from Parker Aerospace

See also

• Astrionics,similar, for spacecraft
• ACARS– Aircraft digital message communication system
• Acronyms and abbreviations in avionics
• ARINC– Aeronautical Radio, Incorporated (1929–2018)
• Avionics software
• DO-178C– International aeronautics software standard
• Emergency locator beacon
• Emergency position-indicating radiobeacon station
• Flight recorder– Aircraft electronic recording device
• Integrated modular avionics

Further reading

• Avionics: Development and Implementationby Cary R. Spitzer (Hardcover – December 15, 2006)
• Principles of Avionics,4th Edition by Albert Helfrick, Len Buckwalter, and Avionics Communications Inc. (Paperback – July 1, 2007)
• Avionics Training: Systems, Installation, and Troubleshootingby Len Buckwalter (Paperback – June 30, 2005)
• Avionics Made Simple,by Mouhamed Abdulla, Ph.D.; Jaroslav V. Svoboda, Ph.D. and Luis Rodrigues, Ph.D. (Coursepack – Dec. 2005 -ISBN978-0-88947-908-1).

External links

• Avionics in Commercial Aircraft
• Aircraft Electronics Association (AEA)
• Pilot's Guide to Avionics
• The Avionic Systems Standardisation Committee
• Space Shuttle Avionics
• Aviation Today Avionics magazine
• RAES Avionics homepage