Anintegrated standby instrument system (ISIS) is an electronic aircraft instrument. It is intended to serve as backup in case of a failure of the standardglass cockpit instrumentation, allowing pilots to continue to receive key flight-related information. Prior to the use of ISIS, this was performed by individual redundant mechanical instrumentation instead. Such systems have become common to be installed in various types of aircraft, ranging fromairliners tohelicopters and smallergeneral aviation aircraft. While it is common for new-built aircraft to be outfitted with ISIS, numerous operators have opted to have their fleets retrofitted with such apparatus as well. Typically there are 3 instruments: an airspeed indicator, an altimeter and an attitude indicator.
An ISIS is designed to combine the functions of separate equivalent mechanical instruments that had previously been included as backup in such cockpits, includingaltimeter,airspeed indicator, andattitude indicator. Various aspects of ISIS are defined by its function of being a backup to conventional instrumentation. In accordance with this principal, it has been designed to operate with a high level of availability and reliability, as well as being as independent as possible from the aircraft's primary instrumentation and sensors alike. It is commonplace for an ISIS to work in conjunction with provisions for auxiliary power (typically abattery unit), as well as harnessing embedded sensors for its readings wherever possible.[1][2] When all onboard instrumentation is performing normally, the readings indicated by an ISIS are identical to that of theprimary flight display.[3] Advantages presented by ISIS over traditional systems include improved safety, greater ease of operation, and reduced operating costs.[4]
A number of aircraft have been produced with relatively sophisticated integrated standby systems which may include additional functions. For example, theRockwell Collins Pro Line 21 flight deck, which is fitted to aircraft such as theCessna Citation XLS+business jet, features a standby navigation display and engine gauges.[5][6]Thales Group produce their own ISIS, which is installed on theAirbus A320narrow-body andAirbus A330wide-body airliners amongst other aircraft; it allowed for one single instrument to replace four standby instruments that had been traditionally used.[7][8] Thales also produced an Integrated Electronic Standby Instrument (IESI) dedicated for use onhelicopters; in excess of 6,000 such units have reportedly been sold as of July 2020.[9] Another such system is manufactured byL3Harris Technologies, intended for both helicopters andgeneral aviation purposes.[3][10] Additional companies specialising in avionics, such asGE Aviation,Smiths Group, andMeggitt, have also marketed ranges of standby instrumentation using both standalone and ISIS-compliance principles.[11][12][13]
Several companies have producedpatentable innovations related to ISIS, including large aerospace players such asAirbus Group.[14] In addition to such technology being adopted upon new-build aircraft, several operators have opted to retrofit their existing aircraft fleets with current generation ISIS, such asUPS'sAirbus A300 freighters.[15] Along these lines, Rockwell Collins developed a retrofit package for theBoeing 757 andBoeing 767 that incorporates ISIS.[16] During the 2010s, the cost of performing such cockpit display retrofits reportedly dropped substantially.[17]
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