Aviation Maintenance Terms
24-bit Address
Unique address assigned to an aircraft during the registration process.
ADS-B Traffic Advisory System (ATAS)
An ADS-B In application that augments flight crew traffic situation awareness in support of the see-and-avoid responsibility by providing alerts of traffic that are detected in conflict with ownship. This application is named Traffic Situation Awareness with Alerts (TSAA) in RTCA DO-317B.
Advisory
The level or category of alert for conditions that require flight crew awareness and may require subsequent flight crew response.
Aircraft Surveillance Application (ASA)
An application that uses aircraft surveillance data to provide benefits to the flight crew (refer to Table 1).
Aircraft Surveillance Applications System (ASAS)
An aircraft system based on airborne surveillance that provides assistance to the flight crew in operating their aircraft relative to other aircraft. Airborne Surveillance and Separation Assurance Processing (ASSAP). The processing subsystem that accepts surveillance inputs (e.g., ADS-B reports), performs surveillance processing to provide reports and tracks, and performs application-specific processing. Surveillance reports, tracks, and any application-specific alerts or guidance are output by ASSAP to the CDTI function. ASSAP surveillance processing consists of track processing and correlation of ADS-B, TIS-B, ADS-R and TCAS reports.
Alert
A general term that applies to all advisories, cautions, and warning information; can include visual, aural, tactile, or other attention-getting methods.
Antenna Offset Parameter
The distance from the nose of the aircraft to the GPS antenna. For large aircraft, this offset is important in accurately placing the aircraft symbol on the airport map.
Application
The function(s) for which the ASA system is used.
Area Navigation (RNAV)
A method of navigation that permits aircraft operation on any desired flight path within the coverage of station-referenced navigation aids or within the limits of the capability of self-contained aids, or a combination of these.
Automatic Dependent Surveillance - Rebroadcast (ADS-R)
Retransmission of UAT ADS-B messages from aircraft on the 1090ES link and 1090ES messages on the UAT link. ADS-R ensures aircraft equipped with different links can receive messages from one another when equipped with ADS-B IN.
Automatic Dependent Surveillance Broadcast (ADS-B)
An advanced surveillance technology where ADS-B OUT equipped aircraft share position, altitude, velocity, and other information with ATC and other appropriately equipped aircraft.
Automatic Dependent Surveillance-Broadcast (ADS-B)
A function on an aircraft or surface vehicle operating within the surface movement area that periodically broadcasts its state vector (horizontal and vertical position, horizontal and vertical velocity) and other information. ADS-B is automatic because no external stimulus is required to elicit a transmission. It is dependent because it relies on on-board navigation sources and on-board broadcast transmission systems to provide surveillance information to other users.
Automatic Dependent Surveillance-Rebroadcast (ADS-R)
A service of the ground system that rebroadcasts ADS-B messages from one link technology onto another. For example, the SBS ground system provides ADS-R service to rebroadcast UAT messages on 1090 MHz and vice versa.
Availability
An indication of the ability of a system or subsystem to provide usable service. Availability is expressed in terms of the probability of the system or subsystem being available at the beginning of an intended operation.
Barometric Altitude Integrity Code (NICBARO)
Indicates if pressure altitude is provided by a single Gillham encoder or another, more robust altitude source. Because of the potential for an undetected error in a Gillham encoding, many Gillham installations are cross-checked against a second altitude source. NICBARO annotates the status of this cross-check.
Basic Airborne (AIRB)
The basic airborne situation awareness application enhances the flight crew’s traffic situation awareness through the provision of an on-board graphical display of surrounding traffic that transmits ADS-B data of a sufficient quality. Pilots will use the CDTI to supplement and enhance out-the-window visual acquisition and listening to radio communications.
Caution
The level or category of alert for conditions that require immediate flight crew awareness and subsequent flight crew response.
CDTI Assisted Visual Separation (CAVS)
The CDTI is used to assist the flight crew in acquiring and maintaining visual contact during visual separation on approach. The CDTI is also used in conjunction with visual, out-the-window contact to follow the preceding aircraft during the approach. The application is expected to improve both the safety and the performance of visual separation on approach. It may allow for the continuation of visual separation on approach even if visual contact out-the-window is momentarily lost.
Coast Interval
The elapsed time since a report from any source has been correlated with the track.
Cockpit Display of Traffic Information (CDTI)
The pilot interface portion of the Aircraft Surveillance Applications System. This interface includes traffic display(s) and all the controls that interact with such a display. At a minimum, CDTI includes a graphical plan-view (top down) traffic display. Additional graphical and non-graphical display surfaces may also be included. The CDTI receives position information of traffic and Ownship from the airborne surveillance and separation assurance processing (ASSAP) function. The ASSAP receives such information from the surveillance sensors and Ownship position sensors.
Conformal
A desirable property of map projections. A map projection (a function that associate points on the surface of an ellipsoid or sphere representing the earth to points on a flat surface such as the CDTI display) is said to be conformal if the angle between any two curves on the first surface is preserved in magnitude and sensed by the angle between the corresponding curves on the other surface.
Controller Pilot Data Link Communication (CPDLC)
Provides direct data communication between the pilot and the air traffic controller through a data link.
Correlation
The process of determining that a new measurement belongs to an existing track.
Data Block
A block of information about selected traffic that is displayed somewhere around the edge of the CDTI display, rather than mixed in with the symbols representing traffic in the main part of the display.
Data Tag
A block of information that is displayed next to the traffic symbol in the main part of the CDTI display.
Designated Application
An application that operates only on specifically-chosen (either by the flight crew or automation) traffic. They generally operate only for a specific flight operation.
Designated Traffic
Traffic upon which a designated application is to be conducted.
Desirable
The capability denoted as desirable is not required to perform the procedure, but would increase the utility of the operation.
Differential Ground Speed
Calculated by taking the difference between the magnitude of the ownship ground speed and the designated traffic ground speed. The assumption is that ownship is following the designated traffic approach path over the ground. Positive values indicate closure on the designated traffic.
Direct Controller Pilot Communication (DCPC)
Direct communication established between the controller and the pilot without having to relay through another unit or going through a secondary means of delivery for that information. Currently, this is accomplished by conventional voice radio operations or CPDLC.
Display Range
The maximum distance from own-ship that is represented on the CDTI display. If the CDTI display is regarded as a map, then longer display ranges correspond to smaller map scales, and short display ranges correspond to larger map scales.
Enhanced Visual Acquisition (EVAcq)
This application is an enhancement for the outthe-window visual acquisition of aircraft traffic and potentially ground vehicles.
Estimation
The process of determining a track’s state based on new measurement information.
Extended Squitter
A long (112 bit) Mode S transmission that is spontaneously produced by the radio as opposed to a response to a Mode S Interrogation. Extended Squitter is the mechanism used to provide ADS-B messages from a Mode S transponder.
Extrapolation
The process of predicting a track’s state forward in time based on the track’s last kinematic state.
Field of View
The field of view of a CDTI is the geographical region within which the CDTI shows traffic. Some documents call this the field of regard.
Flight Crew
One or more cockpit crew members required for the operation of the aircraft.
Flight Information Service Broadcast (FIS-B)
FIS-B is a ground broadcast service provided over the UAT data link. The FAA FIS-B system provides pilots and flight crews of properly equipped aircraft with a cockpit display of certain aviation weather and aeronautical information.
Flight Information System - Broadcast (FIS-B)
A ground broadcast service provided over the UAT data link. The FAA FIS-B system provides pilots and flightcrews of properly equipped aircraft with a cockpit display of certain aviation weather and aeronautical information.
Flight Manual
A generic term used throughout this AC to represent the AFM, RFM, AFM supplement, or RFM supplement.
Galileo
A European satellite-based radio navigation system being developed that will provide a global positioning service.
Global Navigation Satellite System (GNSS)
The generic term for a satellite navigation system, such as GPS, that provides autonomous worldwide geo-spatial positioning and may include local or regional augmentations.
Global Positioning System (GPS)
A U.S. satellite-based radio navigation system that provides a global positioning service. The service provided by GPS for civil use is defined in the Global Positioning System Standard Positioning Service Performance Standard, 4th edition, dated September 2008, available at http://www.gps.gov/technical/ps/2008-SPS-performance- standard.pdf.
GNSS Time of Applicability
The time when the position output from the GNSS sensor is applicable.
GNSS Time of Measurement (TOM)
The time when the last GNSS signal used to determine the position arrives at the aircraft GNSS antenna.
Ground Speed
The magnitude of the horizontal velocity vector (see velocity). In these minimum operational performance standards (MOPS) it is always expressed relative to a frame of reference that is fixed with respect to the earth’s surface such as the WGS-84 ellipsoid.
Ground Track Angle
The direction of the horizontal velocity vector (see velocity) relative to the ground as noted in ground speed.
Hazard Classification
Refer to AC 25-1309-1(), System Design and Analysis, or AC 23.1309-1(), System Safety Analysis and Assessment for Part 23 Airplanes, as applicable.
Horizontal Figure of Merit (HFOM )
The radius of a circle in the horizontal plane, with its center being at the true position, that describes the region assured to contain the indicated horizontal position with at least 95 percent probability under fault-free conditions at the time of applicability.
Horizontal Protection Level Fault Detection (HPLFD)
The radius of a circle in the horizontal plane, with its center being at the true position, that describes the region assured to contain the indicated horizontal position. HPLFD is a horizontal region where the missed alert and false alert requirements are met for the chosen set of satellites when autonomous fault detection is used. It is a function of the satellite and user geometry and the expected error characteristics; it is not affected by actual measurements. Its value is predictable given reasonable assumptions regarding the expected error characteristics.
Horizontal Protection Level Fault Free (HPLFF)
Fault-free horizontal protection level. Refer to RTCA/DO-229D.
Horizontal Velocity
The component of velocity in a local horizontal plane. For Global Positioning System (GPS) sensors, that plane is tangent to the WGS-84 ellipsoid and is vertically displaced such that it contains the navigation sensors’ reference point. For inertial navigation system (INS) equipment, the local plane is perpendicular to the local gravity vector.
In-Trail Procedure (ITP)
A procedure that allows an aircraft to climb-through or descend-through another aircraft’s altitude in order to make a desired flight level change.
International Civil Aviation Organization (ICAO)
A United Nations organization that is responsible for developing international standards, and recommending practices, and procedures covering a variety of technical fields of aviation.
Latency
The time incurred between two particular interfaces. Total latency is the delay between the time of a measurement and the time that the measurement is reported at a particular interface (the latter minus the former). Components of the total latency are elements of the total latency allocated between different interfaces. Each latency component will be specified by naming the interfaces between which it applies.
Mode Control Panel
The Mode Control Panel, (MCP) contains controls that allow aircrew to interface with the autopilot system. The MCP can be used to instruct the autopilot to perform tasks such as; hold a specific altitude, change altitudes at a specific rate, hold a specific heading, turn to a new heading, and or follow the directions of a flight management computer. The MCP is not the autopilot, it just controls the mode in which the autopilot operates.
Nautical Mile (NM)
A unit of length used in the fields of air and marine navigation. In this document, a nautical mile is always the international nautical mile of 1852 m exactly.
Navigation Accuracy Category for Position (NACP)
Used to indicate, with 95 percent certainty, the accuracy of the aircraft reported horizontal position. A NACP of 8 or greater is required by § 91.227.
Navigation Integrity Category (NIC)
A parameter that specifies an integrity containment radius. A NIC of 7 or greater is required by § 91.227.
Navigational Accuracy Category for Velocity (NACV)
Used to indicate, with 95 percent certainty, the accuracy of the aircraft reported horizontal velocity. A NACV of 1 or greater is required by § 91.227.
Own-ship
From the perspective of a flight crew, or of the ASSAP and CDTI functions used by that flight crew, the own-ship is the ASA participant (aircraft or vehicle) that carries that flight crew and those ASSAP and CDTI functions.
Position Source
The on-board avionics equipment that provides the latitude, longitude, geometric altitude, velocity, position and velocity accuracy metrics, and position integrity metric. Additionally, the position source may provide the vertical rate parameters.
Pressure Altitude
Altitude reported by a barometric pressure altimeter without corrections for local pressure settings.
Primary Surveillance Radar (PSR)
A radar sensor that listens for the echoes of pulses that it transmits to illuminate aircraft targets. PSR sensors, in contrast to secondary surveillance radar (SSR) sensors, do not depend on the carriage of transponders on board the aircraft targets.
Range Reference
The CDTI feature of displaying range rings or other range markings at specified radii from the own-ship symbol.
Receiver Autonomous Integrity Monitoring (RAIM)
Any algorithm that verifies the integrity of the position output using GPS measurements, or GPS measurements and barometric aiding, is considered a RAIM algorithm. An algorithm that uses additional information (such as a multi-sensor system with inertial reference system) to verify the integrity of the position output may be acceptable as a RAIM equivalent. Within this AC, the term RAIM is a synonym for aircraft-based augmentation system (ABAS) and is used to refer to both RAIM and RAIM-equivalent algorithms.
Reference Aircraft
An aircraft within the ITP geometric criteria for usage as reference when requesting an ITP clearance.
Satellite-Based Augmentation System (SBAS)
A wide coverage augmentation system in which the user receives augmentation information from a satellite-based transmitter. In the United States, this is referred to as Wide Area Augmentation System (WAAS).
Secondary Surveillance Radar (SSR)
A radar sensor that listens to replies sent by transponders carried on board airborne targets. SSR sensors, in contrast to primary surveillance radar (PSR) sensors, require the aircraft under surveillance to carry a transponder.
Selected Traffic
Traffic for which additional information is requested by the flight crew.
Selective Availability (SA)
A protection technique employed by the Department of Defense that degraded GPS accuracy. Selective availability was discontinued on May 1, 2000.
Sensor
A measurement device. An air data sensor measures atmospheric pressure and temperature, to estimate pressure altitude, and pressure altitude rate, airspeed, etc. A primary surveillance radar sensor measures its antenna direction and the times of returns of echoes of pulses that it transmits to determine the ranges and bearings of airborne targets. A secondary surveillance radar sensor measures its antenna direction and the times of returns of replies from airborne transponders to estimate the ranges and bearings of airborne targets carrying those transponders.
Separation
The minimum distance between aircraft/vehicles allowed by regulations. Separation requirements vary by factors such as radar coverage (none, single, composite), domain (terminal, en route, oceanic), and flight rules (instrument or visual).
Simple Action
A flight crew action that may be performed within a short period of time and without requiring significant concentration that would distract from the main aviation tasks (e.g., a button press). Please refer to AC 25-11( ) for more details.
Source Integrity Level (SIL)
The probability of the reported horizontal position exceeding the radius of containment defined by the NIC without alerting, assuming the avionics has no faults. A SIL of 3 is required by § 91.227.
Spacing
A distance maintained from another aircraft for specific operations.
State Vector
An aircraft’s current horizontal position, vertical position, horizontal velocity, vertical velocity, and navigational accuracy and integrity.
System Design Assurance (SDA)
The failure condition that the position transmission chain is designed to support. An SDA of 2 or greater is required by § 91.227. Refer to A.2.29 for more information.
TCAS Potential Threat
Traffic detected by TCAS equipment on board the own-ship, that has met the Potential Threat classification criteria for a TCAS TA and does not meet the Threat Classification criteria for a TCAS RA (RTCA/DO-185B § 1.8). If the ASAS own- ship CDTI display is also used as a TCAS TA display, then information about TCAS potential threats will be conveyed to the CDTI via the ASSAP function.
TCAS Proximate Traffic
Traffic, detected by TCAS equipment on board the own-ship, that is within 1200 feet vertically and 6 NM horizontally of the own-ship (RTCA/DO-185B § 1.8). If the ASA system own-ship CDTI display is also used as a TCAS display, then information about TCAS proximate traffic will be conveyed to the CDTI, possibly via the ASSAP function.
TCAS-Only Traffic
A traffic element about which TCAS has provided surveillance information, but which the ASSAP function has not correlated with traffic from other surveillance sources such as ADS-B, ADS-R, or TIS-B.
Time of Applicability
The time that a particular measurement or parameter is (or was) relevant.
Total Latency
The total time between when the position is measured by the position source (GNSS TOM for GNSS systems) and when the position is transmitted from the aircraft (ADS-B time of transmission).
Track
(1) A sequence of reports from the ASSAP function that all pertain to the same traffic target. (2) Within the ASSAP function, a sequence of estimates of traffic target state that all pertain to the same traffic element.
Track Angle
See Ground Track Angle.
Track State
See State Vector.
Traffic
All aircraft/vehicles that are within the operational vicinity of own-ship.
Traffic Collision Avoidance System
Collision Avoidance systems which rely on transponder interrogations and replies of other airborne aircraft.
Traffic Collision Avoidance System I
TCAS I is the first generation of collision avoidance technology. TCAS I systems are able to monitor the traffic situation around an aircraft and offer information on the approximate bearing and altitude of other aircraft. It can also generate collision warnings in the form of a "Traffic Advisory" (TA). The TA warns the pilot that another aircraft is in near vicinity, announcing "Traffic, traffic", but does not offer any suggested remedy Traffic Collision Avoidance System II.
Traffic Element
An aircraft or vehicle.
Traffic Information Service - Broadcast (TIS-B)
TIS-B is a ground broadcast service provided from an ADS-B ground system network over the UAT and 1090ES links that provides position, velocity, and other information on traffic detected by a secondary surveillance radar, but is not transmitting an ADS-B position.
Traffic Information Service – Broadcast (TIS-B)
A surveillance service that broadcasts traffic information derived from one or more ground surveillance sources to suitably equipped aircraft or surface vehicles, with the intention of supporting ASA applications.
Traffic Selection
Manual process of flight crew selecting a traffic element.
Traffic Symbol
A depiction on the CDTI display of an aircraft or vehicle other than the own-ship.
Traffic-To-Follow
A term used for CAVS which is used to refer to the aircraft preceding ownship.
Transponder
A piece of equipment carried on board an aircraft to support the surveillance of that aircraft by secondary surveillance radar sensors. A transponder receives interrogation signals on 1030 MHz and replies on the 1090 MHz downlink frequency.
Uncompensated Latency
Any latency in the ADS-B system that is not compensated through extrapolation. Uncompensated latency can be represented as the difference between the time of applicability of the broadcast position and the actual time of transmission.
Universal Access Transceiver (UAT)
A wideband multipurpose data link intended to operate globally on a single channel with a channel signaling rate of just over 1Mbps. By design, UAT supports multiple broadcast services including FIS-B and TIS-B in addition to ADS-B. This is accomplished using a hybrid medium access approach that incorporates both time-slotted and random unslotted access.
Velocity
The rate of change of position. Horizontal velocity is the horizontal component of velocity and vertical velocity is the vertical component of velocity.
Visual Separation on Approach (VSA)
The CDTI is used to assist the flight crew in acquiring and maintaining visual contact during visual separation on approach. The CDTI is also used in conjunction with visual, out-the-window contact to follow the preceding aircraft during the approach. The application is expected to improve both the safety and the performance of visual separation on approach. It may allow for the continuation of visual separation on approach when they otherwise would have to be suspended due to the difficulty of visually acquiring and tracking the other preceding aircraft.
Warning
The level or category of alert for conditions that require immediate flight crew awareness and immediate flight crew response.
Wide Area Augmentation System (WAAS)
The U.S. implementation of SBAS.
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