This glossary highlights specialized terminology used across Aerospace & Defense, with a focused reference for the Avionics, Sensors & Uncrewed Systems Practice. It helps executives and practitioners navigate avionics architectures, sensing technologies, uncrewed operations, certification, safety, data links, navigation, and performance discussions.
A B C D E F G H I J L M N O P R S T U V W
| A | |
| ABAS | Aircraft-Based Augmentation System: An onboard system that augments Global Navigation Satellite System information to improve navigation integrity, availability, or accuracy without relying on an external augmentation service. |
| ACARS | Aircraft Communications Addressing and Reporting System: A digital data-link system used to exchange operational messages between aircraft and ground organizations over VHF, satellite, or other communications networks. |
| ACAS | Airborne Collision Avoidance System: An independent surveillance and alerting system that assesses collision threats and can issue traffic or resolution advisories to help prevent midair collisions. |
| ACAS Xu | Airborne Collision Avoidance System Xu: A collision-avoidance logic designed for larger uncrewed aircraft, integrating surveillance information with maneuver guidance suitable for remotely piloted operations. |
| ADC | Air Data Computer: An avionics computer that converts pitot-static and temperature measurements into parameters such as altitude, airspeed, vertical speed, and Mach number. |
| ADIRU | Air Data Inertial Reference Unit: An integrated avionics unit that supplies air-data, attitude, position, heading, and inertial-navigation information to flight-control and display systems. |
| ADS-B | Automatic Dependent Surveillance–Broadcast: A cooperative surveillance technology through which aircraft broadcast identity, position, altitude, velocity, and related data for air traffic and airborne situational awareness. |
| AESA | Active Electronically Scanned Array: A radar architecture using many independently controlled transmit-receive modules to steer beams electronically, enabling rapid scanning, tracking, and multifunction operation. |
| AFDX | Avionics Full-Duplex Switched Ethernet: A deterministic Ethernet-based avionics network, standardized through ARINC 664 Part 7, that supports redundant and bounded-latency data communications. |
| AGL | Above Ground Level: Altitude measured relative to the terrain directly beneath an aircraft, widely used for operating limits, obstacle clearance, sensor geometry, and uncrewed-flight regulations. |
| AHRS | Attitude and Heading Reference System: A sensor system that combines inertial and magnetic measurements to provide aircraft roll, pitch, yaw, and heading information. |
| AOA | Angle of Attack: The angle between an airfoil’s reference line and the oncoming airflow; sensors measuring it support stall warning, envelope protection, and flight-control functions. |
| APNT | Alternative Positioning, Navigation, and Timing: Technologies that preserve essential navigation and timing services when satellite-based signals are unavailable, degraded, jammed, or spoofed. |
| ARINC | Aeronautical Radio, Incorporated: The name associated with a widely used family of standards governing avionics data buses, communications, software partitioning, equipment interfaces, and form factors. |
| ARINC 429 | Aeronautical Radio, Incorporated Specification 429: A unidirectional digital data-bus standard that defines electrical, data-word, and transmission characteristics for communications among commercial avionics equipment. |
| ARINC 653 | Aeronautical Radio, Incorporated Specification 653: A standard defining time and space partitioning services for safety-critical avionics operating systems, particularly within integrated modular avionics architectures. |
| ARINC 664 | Aeronautical Radio, Incorporated Specification 664: A family of standards describing Ethernet-based aircraft data networks, including the deterministic network provisions commonly associated with AFDX. |
| ARP4754A | Guidelines for Development of Civil Aircraft and Systems: An SAE Aerospace Recommended Practice that structures aircraft and system development, requirements allocation, validation, verification, and development assurance. |
| ARP4761A | Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment: An SAE Aerospace Recommended Practice providing methods for evaluating aircraft and system hazards, failure conditions, and safety requirements. |
| ASTM | ASTM International: A consensus standards organization whose specifications address areas such as small-aircraft design, uncrewed-aircraft systems, remote identification, operations, and traffic-management interoperability. |
| B | |
| BIT | Built-In Test: An onboard diagnostic function that detects, isolates, and reports equipment faults during startup, operation, or commanded maintenance testing. |
| BITE | Built-In Test Equipment: Hardware and software embedded in an avionics unit to execute diagnostics, record fault information, and support troubleshooting and dispatch decisions. |
| BLOS | Beyond Line of Sight: A communications condition in which the aircraft and control station cannot connect through a direct radio path, requiring relays, satellite links, or network infrastructure. |
| BMS | Battery Management System: Electronics that monitor and control battery voltage, current, temperature, state of charge, balancing, and protective functions in electrically powered aircraft and payloads. |
| BVLOS | Beyond Visual Line of Sight: An uncrewed-aircraft operation conducted beyond the remote pilot’s unaided visual observation, typically requiring additional approvals, communications, surveillance, and risk mitigations. |
| C | |
| C2 | Command and Control: The functions and communications used by a remote pilot or automated controller to direct an uncrewed aircraft and monitor its status. |
| CAA | Civil Aviation Authority: A national regulator responsible for areas such as aircraft certification, airworthiness, operating approvals, airspace access, and oversight of uncrewed operations. |
| CAN | Controller Area Network: A robust serial communications bus used to connect distributed controllers, sensors, actuators, propulsion components, and payload equipment. |
| CCA | Common Cause Analysis: A safety-assessment activity that examines whether shared resources, environments, installations, or events could defeat otherwise independent systems or protections. |
| CCA | Circuit Card Assembly: A populated printed circuit board forming a functional electronic module within an avionics computer, sensor, display, communications unit, or controller. |
| CCD | Charge-Coupled Device: An image-sensor technology that converts incident light into electrical charge for applications requiring controlled readout and high image quality. |
| CEP | Circular Error Probable: A statistical measure of horizontal positional or targeting accuracy, expressed as the radius within which a specified proportion of observations is expected to fall. |
| CMOS | Complementary Metal-Oxide-Semiconductor: A semiconductor technology widely used in imaging arrays and digital electronics because of its low power consumption, integration capability, and high-speed readout. |
| CNPC | Control and Non-Payload Communications: Communications supporting safe control and monitoring of an uncrewed aircraft, distinct from links carrying mission-payload data. |
| CNS | Communications, Navigation, and Surveillance: The combined technical capabilities enabling aircraft connectivity, position determination, route execution, and visibility to traffic-management systems. |
| CONOPS | Concept of Operations: A structured description of intended missions, users, environments, system behavior, interfaces, and operating procedures used to guide design and regulatory evaluation. |
| COTS | Commercial Off-the-Shelf: Hardware or software procured from the commercial market rather than developed specifically for a program, requiring careful assessment of assurance, configuration, obsolescence, and environmental suitability. |
| C-UAS | Counter-Unmanned Aircraft Systems: Sensors, command systems, and mitigation technologies used to detect, identify, track, assess, and respond to unauthorized or threatening uncrewed aircraft. |
| D | |
| DAA | Detect and Avoid: The capability to identify collision hazards and execute or recommend avoidance actions, enabling uncrewed aircraft to meet applicable see-and-avoid responsibilities. |
| DAL | Design Assurance Level: A classification linking the severity of potential failure effects to the rigor required for system, software, or electronic-hardware development assurance. |
| DAS | Distributed Aperture System: A network of sensors positioned around an aircraft to provide wide-area or spherical coverage for awareness, warning, tracking, and enhanced vision. |
| DGPS | Differential Global Positioning System: A positioning method that applies corrections from known reference locations to reduce common satellite-navigation errors and improve accuracy. |
| DIRCM | Directional Infrared Countermeasures: A protective system that detects infrared-guided threats and directs modulated energy toward their seekers to disrupt tracking. |
| DME | Distance Measuring Equipment: A radio-navigation system that determines slant-range distance between an aircraft interrogator and a ground transponder. |
| DMSMS | Diminishing Manufacturing Sources and Material Shortages: The loss or impending loss of component and material availability, a significant lifecycle risk for long-lived avionics and sensor programs. |
| DO-160G | Environmental Conditions and Test Procedures for Airborne Equipment: An RTCA standard defining laboratory tests for environmental conditions such as temperature, vibration, electromagnetic effects, fluids, and lightning exposure. |
| DO-178C | Software Considerations in Airborne Systems and Equipment Certification: The primary civil-aviation guidance for developing and verifying airborne software with rigor proportionate to its safety impact. |
| DO-254 | Design Assurance Guidance for Airborne Electronic Hardware: RTCA guidance governing the development and assurance of complex airborne electronic hardware such as field-programmable gate arrays and application-specific integrated circuits. |
| DO-326A | Airworthiness Security Process Specification: An RTCA standard defining processes for addressing intentional unauthorized electronic interaction during aircraft and system development and certification. |
| DO-356A | Airworthiness Security Methods and Considerations: RTCA guidance describing methods for security risk assessment, requirements development, verification, and substantiation of aircraft-system cybersecurity. |
| DO-362A | Command and Control Data Link Minimum Operational Performance Standards for Terrestrial Systems: An RTCA standard establishing performance expectations for terrestrial links used to command and monitor uncrewed aircraft. |
| DO-365C | Minimum Operational Performance Standards for Detect and Avoid Systems: An RTCA standard defining performance criteria for surveillance, alerting, guidance, and related functions that support collision avoidance by uncrewed aircraft. |
| DSP | Digital Signal Processing: The mathematical processing of sampled signals for functions such as filtering, detection, tracking, image enhancement, compression, and sensor fusion. |
| DSSS | Direct-Sequence Spread Spectrum: A radio technique that spreads a signal across a wider bandwidth using a coded sequence, improving interference tolerance and supporting robust data links. |
| E | |
| EASA | European Union Aviation Safety Agency: The European Union agency responsible for civil-aviation safety rules, certification specifications, approvals, and regulatory frameworks covering aircraft and uncrewed operations. |
| EGPWS | Enhanced Ground Proximity Warning System: A terrain-awareness system that combines aircraft state, position, and terrain databases to provide predictive warnings of potential controlled flight into terrain. |
| ELT | Emergency Locator Transmitter: An onboard distress beacon intended to transmit identifying and location information after an accident or manual activation. |
| EMC | Electromagnetic Compatibility: The ability of electronic equipment to operate correctly in its electromagnetic environment without causing unacceptable interference to other systems. |
| EMI | Electromagnetic Interference: Unwanted electromagnetic energy that can degrade sensors, navigation receivers, communications links, flight controls, or other electronic equipment. |
| EO | Electro-Optical: Technologies that detect or manipulate electromagnetic energy in visible and adjacent spectral bands for imaging, tracking, inspection, mapping, or targeting. |
| EO/IR | Electro-Optical/Infrared: A combined sensor category covering visible-light and infrared imaging systems used for surveillance, navigation, inspection, situational awareness, and target recognition. |
| ESC | Electronic Speed Controller: A power-electronics device that regulates electric-motor speed and torque, commonly controlling propulsion motors in multirotor and fixed-wing uncrewed aircraft. |
| ESM | Electronic Support Measures: Passive sensing functions that detect, intercept, identify, locate, and analyze electromagnetic emissions for threat warning and situational awareness. |
| ESS | Environmental Stress Screening: A production process that applies controlled stresses to reveal latent manufacturing defects in electronic assemblies before field deployment. |
| ETSO | European Technical Standard Order: A European minimum-performance standard under which eligible aircraft articles may receive an authorization demonstrating compliance with defined technical requirements. |
| EVLOS | Extended Visual Line of Sight: An operating method in which trained observers extend the area over which an uncrewed aircraft remains under continuous visual observation. |
| eVTOL | Electric Vertical Takeoff and Landing: An electrically propelled aircraft configuration capable of vertical takeoff and landing, often relying on highly integrated flight controls, sensors, and distributed propulsion. |
| F | |
| FAA | Federal Aviation Administration: The United States authority responsible for civil-aircraft certification, operational regulation, airspace management, and oversight of uncrewed-aircraft activities. |
| FACE | Future Airborne Capability Environment: An open avionics software standard and business approach intended to improve software portability, interoperability, reuse, and supplier competition across military airborne platforms. |
| FADEC | Full Authority Digital Engine Control: A digital control system with full authority over engine operation, optimizing performance while managing limits, sequencing, monitoring, and fault responses. |
| FCC | Federal Communications Commission: The United States regulator governing nonfederal radio-frequency use, equipment authorization, and spectrum rules affecting many uncrewed-aircraft and data-link products. |
| FCS | Flight Control System: The sensors, computers, software, actuators, and interfaces that command and stabilize an aircraft’s attitude, trajectory, and configuration. |
| FHA | Functional Hazard Assessment: A safety-analysis method that identifies aircraft or system functions, evaluates failure conditions, and classifies their potential effects and severity. |
| FHSS | Frequency-Hopping Spread Spectrum: A radio technique that rapidly changes carrier frequencies according to a shared sequence to improve resilience against interference and narrowband disruption. |
| FLIR | Forward-Looking Infrared: A thermal-imaging capability oriented in the direction of travel or observation to support night operations, detection, navigation, surveillance, and targeting. |
| FMCW | Frequency-Modulated Continuous Wave: A radar technique that varies transmitted frequency continuously and measures return-frequency differences to estimate range and relative velocity. |
| FMEA | Failure Modes and Effects Analysis: A systematic bottom-up method for identifying how components may fail and evaluating the resulting effects on higher-level functions or systems. |
| FMECA | Failure Modes, Effects, and Criticality Analysis: An extension of failure-mode analysis that evaluates or ranks failure criticality to focus design controls, testing, and risk reduction. |
| FMS | Flight Management System: An integrated avionics function that supports route planning, navigation, performance calculations, guidance, and interaction with aircraft displays and controls. |
| FOV | Field of View: The angular area observable by a sensor or optical system, influencing coverage, search rate, resolution, and target-acquisition performance. |
| FPA | Focal Plane Array: A two-dimensional detector array positioned at an optical system’s focal plane to capture visible, infrared, or other electromagnetic imagery. |
| FPGA | Field-Programmable Gate Array: A reconfigurable integrated circuit used for deterministic, high-speed processing, interface management, sensor pipelines, and flight-control functions. |
| FRACAS | Failure Reporting, Analysis, and Corrective Action System: A closed-loop process for recording failures, determining root causes, implementing corrective actions, and tracking reliability improvement. |
| FTA | Fault Tree Analysis: A deductive safety-analysis technique that models combinations of lower-level faults capable of producing a defined hazardous event. |
| FTS | Flight Termination System: A safety system capable of ending or containing a flight when continued operation creates an unacceptable risk to people, property, or controlled airspace. |
| G | |
| GBAS | Ground-Based Augmentation System: A local satellite-navigation augmentation system that broadcasts corrections and integrity information to support precise approach and landing operations. |
| GCS | Ground Control Station: The equipment and interfaces from which personnel plan, command, monitor, and manage an uncrewed aircraft and its mission payloads. |
| GMTI | Ground Moving Target Indication: A radar processing capability that detects and tracks moving objects on the ground by separating their Doppler signatures from stationary clutter. |
| GNC | Guidance, Navigation, and Control: The integrated functions that determine vehicle state, generate desired trajectories, and command actuators to follow those trajectories safely and accurately. |
| GNSS | Global Navigation Satellite System: The collective term for satellite constellations and supporting systems that provide positioning, navigation, and timing services worldwide. |
| GPS | Global Positioning System: The United States satellite-navigation constellation used extensively for aircraft position, velocity, time, navigation, guidance, and sensor georeferencing. |
| GRC | Ground Risk Class: A SORA classification representing the intrinsic risk that an uncrewed-aircraft operation poses to people and property on the ground. |
| GSD | Ground Sample Distance: The ground dimension represented by one image pixel, commonly used to specify mapping, inspection, and reconnaissance image resolution. |
| H | |
| HALE | High-Altitude Long-Endurance: A class of uncrewed aircraft designed to operate at high altitude for extended periods, often supporting persistent sensing, communications, or surveillance missions. |
| HAPS | High-Altitude Platform Station: An ITU-recognized radio station carried on an object operating in the stratosphere to provide communications or related services over a wide area. |
| HAPS | High-Altitude Pseudo-Satellite: A long-endurance stratospheric aircraft intended to provide persistent capabilities resembling those of satellites, including communications relay, observation, and environmental monitoring. |
| HIL | Hardware-in-the-Loop: A test method that connects real avionics or control hardware to a real-time simulation of the aircraft, sensors, actuators, and operating environment. |
| HMI | Human-Machine Interface: The controls, displays, alerts, and interaction logic through which pilots, operators, and maintainers monitor and direct aircraft systems. |
| HUD | Head-Up Display: A display that presents flight, navigation, targeting, or sensor information within the operator’s forward field of view. |
| I | |
| ICAO | International Civil Aviation Organization: The United Nations specialized agency that establishes international standards and recommended practices for civil aviation, including remotely piloted aircraft integration. |
| ICD | Interface Control Document: A controlled specification defining the physical, electrical, data, timing, protocol, and functional interfaces between systems or components. |
| IFF | Identification Friend or Foe: A cooperative identification system using coded interrogations and replies to help distinguish friendly platforms and support airspace situational awareness. |
| IFOV | Instantaneous Field of View: The angular area observed by a single detector element, helping determine a sensor’s spatial resolution at a given range. |
| ILS | Instrument Landing System: A ground-based radio-navigation system providing lateral and vertical guidance to properly equipped aircraft during approach and landing. |
| IMA | Integrated Modular Avionics: An architecture that hosts multiple aircraft functions on shared, partitioned computing and networking resources rather than separate dedicated computers. |
| IMU | Inertial Measurement Unit: A sensor assembly containing accelerometers and gyroscopes, and sometimes magnetometers, to measure linear acceleration and angular motion. |
| INS | Inertial Navigation System: A navigation system that estimates position, velocity, and attitude from inertial measurements, usually aided by satellite or other external observations. |
| IR | Infrared: Electromagnetic radiation beyond visible red light used for thermal imaging, target detection, tracking, navigation, warning, and environmental sensing. |
| IRST | Infrared Search and Track: A passive sensor capability that detects and tracks airborne or surface targets by their infrared signatures without transmitting radio-frequency energy. |
| ISR | Intelligence, Surveillance, and Reconnaissance: Coordinated collection and analysis activities that use airborne sensors and communications to develop situational awareness and decision-quality information. |
| J | |
| JARUS | Joint Authorities for Rulemaking on Unmanned Systems: An international group of aviation authorities that develops harmonized technical, safety, and operational guidance for uncrewed-aircraft regulation. |
| L | |
| LAANC | Low Altitude Authorization and Notification Capability: An FAA system that automates requests and notifications for eligible drone operations in controlled airspace near participating airports. |
| LiDAR | Light Detection and Ranging: A sensing method that measures reflected laser pulses to determine distance and create precise three-dimensional representations of terrain, structures, or objects. |
| LOS | Line of Sight: A direct, substantially unobstructed propagation path between communicating or sensing systems, affecting link availability, detection range, and operating geometry. |
| LRU | Line-Replaceable Unit: A modular aircraft component designed for replacement at the operating location, simplifying installation, fault isolation, configuration control, and service restoration. |
| LUC | Light UAS Operator Certificate: An EASA-framework organizational approval that can grant qualified uncrewed-aircraft operators privileges to authorize certain operations under defined conditions. |
| LWIR | Long-Wave Infrared: An infrared spectral band commonly used for thermal imaging because objects near ambient temperatures emit strongly within it. |
| LWS | Laser Warning System: A sensor system that detects, characterizes, and may locate incident laser energy to alert an aircraft to designation, ranging, or guidance threats. |
| M | |
| MALE | Medium-Altitude Long-Endurance: A class of uncrewed aircraft optimized for sustained operations at medium altitudes, commonly carrying surveillance, communications, or mission payloads. |
| MAVLink | Micro Air Vehicle Link: A lightweight messaging protocol used by many uncrewed systems to exchange commands, telemetry, status, mission, and payload information. |
| MAWS | Missile Approach Warning System: An aircraft self-protection sensor that detects and tracks approaching missiles to trigger alerts and coordinated countermeasure responses. |
| MEMS | Microelectromechanical Systems: Miniaturized mechanical and electronic structures used in compact accelerometers, gyroscopes, pressure sensors, microphones, and other airborne sensing devices. |
| MFD | Multifunction Display: An avionics display that presents selectable flight, navigation, engine, communications, mission, weather, or sensor information. |
| MIL-STD | Military Standard: A United States defense standard designation covering technical requirements such as environmental qualification, interfaces, electromagnetic compatibility, manufacturing, and interoperability. |
| MIMO | Multiple-Input Multiple-Output: A communications or radar technique using multiple transmit and receive channels to improve capacity, reliability, coverage, or spatial discrimination. |
| MOPS | Minimum Operational Performance Standards: Consensus specifications defining the minimum performance needed for airborne equipment or systems to support particular operational functions. |
| MOSA | Modular Open Systems Approach: A strategy emphasizing modular design, widely supported standards, defined interfaces, and competitive component replacement to improve interoperability and lifecycle flexibility. |
| MSL | Mean Sea Level: A reference surface used to express altitude independently of the terrain directly beneath an aircraft. |
| MTBF | Mean Time Between Failures: A reliability measure representing the expected operating time between successive failures of a repairable item under stated conditions. |
| MTF | Modulation Transfer Function: A measure of how effectively an imaging system preserves contrast at different spatial frequencies, providing a key indicator of optical performance and resolution. |
| MTI | Moving Target Indication: Radar processing that distinguishes moving targets from stationary clutter by exploiting differences in returned-signal frequency or phase. |
| MWIR | Mid-Wave Infrared: An infrared spectral band used in thermal imaging, tracking, and detection systems, especially where hot targets or long-range performance are important. |
| N | |
| NAS | National Airspace System: The interconnected United States system of airspace, airports, navigation facilities, surveillance, communications, procedures, regulations, and traffic-management services. |
| NETD | Noise-Equivalent Temperature Difference: A thermal-imager sensitivity metric indicating the smallest temperature difference that can be distinguished above system noise; lower values generally indicate greater sensitivity. |
| NIR | Near-Infrared: The infrared band closest to visible light, used for low-light imaging, vegetation analysis, material discrimination, illumination, and other sensing applications. |
| NOTAM | Notice to Air Missions: A time-critical notice communicating temporary or abnormal information about airspace, facilities, procedures, hazards, or services relevant to flight operations. |
| NUC | Non-Uniformity Correction: Image-processing calibration that compensates for pixel-to-pixel response differences in detector arrays, particularly in infrared imaging systems. |
| NVG | Night Vision Goggles: Head-worn image-intensification equipment that improves low-light vision and imposes compatibility requirements on cockpit lighting, displays, and indicators. |
| O | |
| ODA | Organization Designation Authorization: An FAA program that authorizes qualified organizations to perform specified certification functions on the agency’s behalf under formal oversight. |
| OFDM | Orthogonal Frequency-Division Multiplexing: A digital modulation method that divides data among closely spaced orthogonal subcarriers, enabling efficient and robust broadband radio links. |
| OMS | Open Mission Systems: A United States Air Force open-architecture standard that defines interfaces and services for integrating mission capabilities, sensors, applications, and subsystems. |
| OSO | Operational Safety Objective: A SORA requirement addressing technical, procedural, organizational, or human safeguards needed to achieve an acceptable level of operational risk. |
| P | |
| PBN | Performance-Based Navigation: An aviation framework specifying required navigation performance rather than prescribing particular sensors, enabling flexible routes and procedures based on qualified capabilities. |
| PDRA | Predefined Risk Assessment: An EASA-defined risk assessment for a recognized uncrewed-aircraft operation, allowing applicants to use established conditions and mitigations instead of conducting a full bespoke assessment. |
| PFD | Primary Flight Display: An integrated display presenting essential flight information such as attitude, airspeed, altitude, heading, vertical speed, and guidance cues. |
| PIC | Pilot in Command: The person with final authority and responsibility for the operation and safety of a flight, including applicable remotely piloted operations. |
| PID | Proportional-Integral-Derivative: A feedback-control method combining present error, accumulated error, and rate of change to regulate aircraft attitude, speed, position, or other variables. |
| PNT | Positioning, Navigation, and Timing: The integrated capabilities that determine location, support movement along a desired path, and provide precise time references to aircraft systems. |
| PPP | Precise Point Positioning: A satellite-navigation technique that uses precise orbit and clock corrections to achieve high positioning accuracy without a nearby local reference station. |
| PRF | Pulse Repetition Frequency: The number of transmitted pulses per second in a radar, lidar, or pulsed sensing system, affecting range and velocity measurement performance. |
| PRI | Pulse Repetition Interval: The elapsed time between successive transmitted pulses, a core parameter in radar waveform design and emitter identification. |
| PSSA | Preliminary System Safety Assessment: A development-stage analysis that evaluates whether a proposed architecture can satisfy allocated safety requirements and identifies necessary independence or protection measures. |
| PWM | Pulse-Width Modulation: A control technique that varies pulse duration to regulate effective power or encode commands for motors, servos, lighting, and other aircraft equipment. |
| R | |
| RA | Resolution Advisory: Collision-avoidance guidance recommending a vertical or other maneuver to resolve a predicted airborne conflict. |
| RADALT | Radar Altimeter: An onboard sensor that measures aircraft height above the terrain by timing or analyzing radio-frequency reflections from the surface below. |
| RAIM | Receiver Autonomous Integrity Monitoring: A satellite-navigation receiver function that checks measurement consistency to detect potentially unreliable positioning information without external integrity data. |
| RCS | Radar Cross Section: A measure of how detectable an object is by radar, influenced by its size, shape, materials, orientation, and operating frequency. |
| RF | Radio Frequency: The electromagnetic-frequency range used by radar, navigation, telemetry, command-and-control, communications, and electronic-support systems. |
| RFI | Radio-Frequency Interference: Unwanted radio-frequency energy that disrupts or degrades communications, navigation, surveillance, or sensor performance. |
| RID | Remote Identification: A capability that broadcasts or communicates identifying, location, and control-station information for an uncrewed aircraft to support accountability and airspace awareness. |
| RLOS | Radio Line of Sight: A direct radio propagation condition between an aircraft and ground or airborne station, subject to terrain, curvature, antenna placement, and atmospheric effects. |
| RNP | Required Navigation Performance: A performance-based navigation specification that includes defined accuracy, integrity, continuity, availability, and onboard monitoring and alerting requirements. |
| RPA | Remotely Piloted Aircraft: An unmanned aircraft flown by a licensed or designated remote pilot from a remote pilot station rather than by a pilot onboard. |
| RPAS | Remotely Piloted Aircraft System: The remotely piloted aircraft together with its control station, command-and-control links, required personnel, and supporting components. |
| RPIC | Remote Pilot in Command: The person responsible for the safe conduct of an uncrewed-aircraft operation and for compliance with applicable operating rules. |
| RTCA | Radio Technical Commission for Aeronautics: A standards-development organization that produces consensus aviation documents used extensively in communications, navigation, surveillance, software, hardware, cybersecurity, and uncrewed-system certification. |
| RTK | Real-Time Kinematic: A carrier-phase satellite-navigation technique using corrections from a reference station or network to deliver centimeter-level positioning under suitable conditions. |
| RWR | Radar Warning Receiver: A passive aircraft sensor that detects and characterizes radar emissions to provide threat awareness, identification, direction finding, and warning. |
| S | |
| SAE | SAE International: A standards organization that publishes aerospace practices and specifications covering systems development, safety assessment, avionics, interfaces, materials, and engineering processes. |
| SAIL | Specific Assurance and Integrity Level: A SORA classification that determines the level of confidence and rigor required for operational safety objectives based on the assessed air and ground risks. |
| SAR | Search and Rescue: Operations conducted to locate and assist people in distress, increasingly supported by uncrewed aircraft carrying imaging, thermal, communications, and location payloads. |
| SAR | Synthetic Aperture Radar: An imaging-radar technique that combines returns collected along a moving flight path to produce high-resolution imagery in darkness and through many weather conditions. |
| SATCOM | Satellite Communications: Communications relayed through satellites to provide long-range or beyond-line-of-sight command, telemetry, voice, and payload-data connectivity. |
| SBAS | Satellite-Based Augmentation System: A regional system that broadcasts satellite-navigation corrections and integrity information to improve accuracy, availability, and safety for aviation users. |
| SDR | Software-Defined Radio: A radio architecture in which functions such as modulation, filtering, waveform generation, and protocol handling are implemented primarily through configurable software. |
| SMS | Safety Management System: A structured organizational framework for managing safety policy, risk, assurance, promotion, accountability, and continuous improvement. |
| SNR | Signal-to-Noise Ratio: The ratio of desired signal power to background noise, used to assess the quality and detection performance of sensors, receivers, and communications links. |
| SORA | Specific Operations Risk Assessment: A structured JARUS methodology used to evaluate uncrewed-aircraft operational risk and determine appropriate technical, procedural, and organizational mitigations. |
| SOSA | Sensor Open Systems Architecture: A consensus open architecture defining modular hardware, software, electrical, and mechanical interfaces for interoperable sensor and processing systems. |
| SSA | System Safety Assessment: A formal analysis demonstrating that a completed system architecture and implementation satisfy allocated safety objectives and requirements. |
| SSR | Secondary Surveillance Radar: A cooperative surveillance system that interrogates aircraft transponders to obtain identity, altitude, and other information in addition to range and bearing. |
| STANAG | Standardization Agreement: A NATO agreement establishing common technical, operational, or administrative standards to improve interoperability among allied forces and systems. |
| STS | Standard Scenario: A predefined EASA operating scenario with specified aircraft, pilot, procedural, and risk-control requirements that can support declaration-based uncrewed operations. |
| sUAS | Small Unmanned Aircraft System: A regulatory and industry category covering a small unmanned aircraft together with its control station, communications links, and associated components. |
| SVS | Synthetic Vision System: An avionics display capability that creates a computer-generated view of terrain, obstacles, runways, and flight-path information from databases and navigation data. |
| SWaP-C | Size, Weight, Power, and Cost: A set of tightly coupled constraints used to evaluate avionics, sensor, payload, and computing solutions for aircraft integration. |
| SWIR | Short-Wave Infrared: An infrared spectral band useful for low-light imaging, haze penetration, moisture detection, and distinguishing materials that appear similar in visible imagery. |
| T | |
| TAWS | Terrain Awareness and Warning System: An onboard safety system that uses aircraft position, flight parameters, and terrain data to warn of potentially hazardous terrain conflicts. |
| TCAS | Traffic Alert and Collision Avoidance System: An airborne system that interrogates nearby transponders, evaluates collision threats, and issues traffic alerts or resolution advisories. |
| TDL | Tactical Data Link: A standardized communications link used to exchange time-sensitive surveillance, identification, command, targeting, and situational-awareness data among platforms. |
| TDOA | Time Difference of Arrival: A geolocation method that estimates a transmitter’s position from differences in signal arrival time at spatially separated receivers. |
| TFR | Temporary Flight Restriction: A short-term restriction placed on aircraft operations within defined airspace for safety, security, disaster response, or other special circumstances. |
| TIS-B | Traffic Information Service–Broadcast: A ground-broadcast service that provides participating aircraft with surveillance-derived traffic information for nearby transponder-equipped aircraft. |
| TSO | Technical Standard Order: An FAA minimum-performance standard for specified aircraft articles; authorization shows that an article’s approved design meets the applicable standard. |
| TTFF | Time to First Fix: The time a navigation receiver requires after startup or reacquisition to produce a valid position solution. |
| U | |
| UA | Unmanned Aircraft: The aircraft component of an unmanned system, operated without a human pilot onboard; the term remains embedded in many regulations and standards. |
| UAS | Unmanned Aircraft System: An unmanned aircraft and the associated control station, communications links, software, equipment, and personnel required for safe operation. |
| UHF | Ultra High Frequency: The radio-frequency band from 300 MHz to 3 GHz, used for various command, telemetry, communications, navigation, and surveillance applications. |
| USS | UAS Service Supplier: An organization providing traffic-management services such as strategic deconfliction, flight-intent sharing, constraint information, conformance monitoring, or remote-identification support. |
| UTM | Unmanned Aircraft System Traffic Management: A distributed ecosystem of services, procedures, data exchanges, and authorities designed to coordinate high-volume uncrewed operations, especially at lower altitudes. |
| V | |
| VHF | Very High Frequency: The radio-frequency band from 30 MHz to 300 MHz, including frequencies widely used for civil aeronautical voice, navigation, and data communications. |
| VLOS | Visual Line of Sight: An operating condition in which the remote pilot or designated observer maintains continuous unaided visual contact sufficient to control the aircraft and avoid hazards. |
| VOR | VHF Omnidirectional Range: A ground-based radio-navigation aid that enables equipped aircraft to determine their bearing relative to the station. |
| VTOL | Vertical Takeoff and Landing: The capability to take off, hover, and land vertically, avoiding the need for a conventional runway and shaping propulsion and flight-control architecture. |
| W | |
| WAAS | Wide Area Augmentation System: The United States satellite-based augmentation system that improves GPS accuracy, integrity, and availability for aviation navigation and approach operations. |
| WAMI | Wide-Area Motion Imagery: An airborne imaging capability that continuously observes a broad geographic area, enabling analysts to track multiple moving objects and reconstruct activity over time. |
| WGS 84 | World Geodetic System 1984: The global geodetic reference system used by GPS and many airborne navigation, mapping, targeting, and sensor-geolocation applications. |
| WMM | World Magnetic Model: A mathematical representation of Earth’s main magnetic field used to convert between magnetic and true heading in navigation systems. |