A satellite data unit (SDU) is an

avionics Avionics (a blend word, blend of ''aviation'' and ''electronics'') are the Electronics, electronic systems used on aircraft. Avionic systems include communications, Air navigation, navigation, the display and management of multiple systems, ...

device installed in an aircraft that allows air/ground communication via a

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...

network. It is an integral part of an aircraft's SATCOM (satellite communication) system. The device connects with a satellite via ordinary

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upp ...

(RF) communication and the satellite then connects to a ground station or ''vice versa''. All satellite communication whether audio or data is processed by the SDU. The SDU communicates with an onboard MDDU (multi-purpose disk-drive unit) which maintains an updatable table of ground stations in the aircraft's current area and the order of preference for selection of which ground station to use which thus guides the choice of satellite. Along with analysing data continuously sent from all ground stations (such as station status and the error rate of signals from each station) the SDU receives information on the aircraft's position and orientation from another onboard system (ADIRU,

air data inertial reference unit An Air Data Inertial Reference Unit (ADIRU) is a key component of the integrated Air Data Inertial Reference System (ADIRS), which supplies air data (airspeed, angle of attack and altitude) and inertial reference (position and attitude) informatio ...

) which it passes to the BSU (beam-steering unit) to direct the signal beam from the aircraft to the chosen satellite. With the advent of cellphones and the Internet a separate or integrated SDU can be used to offer telephone and Internet services to passengers.A330 TECHNICAL TRAINING MANUAL MECHANICAL & AVIONICS COURSE, pages 58 - 69, copyright Airbus S.A.S, published before 2014, but copyright date not given Logs of satellite communication have been used to inform

search and rescue Search and rescue (SAR) is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields, typically determined by the type of terrain the search ...

agencies of locations of missing aircraft, notably that of

Malaysia Airlines Flight 370 Malaysia Airlines Flight 370 (MH370/MAS370) was an international passenger flight operated by Malaysia Airlines that disappeared on 8 March 2014 while flying from Kuala Lumpur International Airport in Malaysia to its planned destination ...

whose position was unknown due to loss of

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

contact and other communications. Automated SATCOM transmissions suggested it flew about off its designated flight path having flown approximately

south-southwest The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each se ...

rather than the intended approximately north-northeast."Information provided to MH370 by AAIB: Information provided to MH370 investigation by UK Air Accidents Investigation Branch (AAIB)". Department of Civil Aviation Malaysia. Retrieved 6 May 2014.

References

Navigational equipment Aircraft instruments Avionics Communications satellites {{aviation-stub