AC 20-191 Appendix A
• L OC ILS Localizer
• MAP Missed Approach Point
• MDA Minimum Descent Altitude
• MLS Microwave Landing System
• MMR Multi-mode Receiver
• MSL Mean Sea Level [altitude reference datum]
• NAVAID Navigational Aid
• NOTAM Notice to Airmen
• PF Pilot Flying
• PFD Primary Flight Display
• QNH Altimeter Setting referenced to airport ambient local pressure
• RDP Runway Datum Point
• RMS Root-mean-square
• RNAV Area Navigation
• RNP Required Navigation Performance
• RPDS Reference Path Data Selector
• RPI Runway Path Identifier
• RVR Runway Visual Range
• SARPs Standards and Recommended Practices (ICAO)
• STC Supplemental Type Certificate
• TC Type Certificate
• TSE Total System Error
• V1 The maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.
• VDB VHF Data Broadcast
• VFAILURE Speed at which failure occurs
• VHF Very High Frequency
• VMC Visual Meteorological Conditions
• VMCG Ground Minimum Control Speed A-3
AC 20-191 Appendix A
• VNA V Vertical Navigation
• WGS-84 World Geological Survey - 1984 A.2 Definitions of Terms.
Term Definition A measure of the current estimated navigation performance,
• Actual excluding Flight Technical Error (FTE). Actual Navigation Navigation Performance is measured in terms of accuracy, integrity, and Performance availability of navigation signals and equipment.
The airborne equipment that senses and computes the aircraft position
• Airborne relative to the defined path, and provides information to the displays Navigation and to the flight guidance system. It may include a number of System receivers or system computers such as a Flight Management Computer (FMC) or both and typically provides inputs to the Flight Guidance System.
A height above the runway based on the characteristics of the aircraft
• Alert Height and its fail-operational landing system, above which a Category III approach would be discontinued and a missed approach initiated if a failure occurred in one of the redundant parts of the fail operational landing system, or in the relevant ground equipment (Manual for All Weather Operations, ICAO Doc. 9365).
• Automatic A go-around that is accomplished by an autopilot following pilot Go-Around selection and initiation of the go-Around autopilot mode, when an autopilot is engaged in an approach mode.
• Availability An expectation that systems or elements required for an operation will be available to perform their intended functions so that the operation will be accomplished as planned to an acceptable level of probability.
• Balked A discontinued landing attempt. This term is often used in Landing conjunction with aircraft configuration or performance assessment, as in “Balked landing climb gradient,” Also, see “Rejected Landing.”
• Category II A precision instrument approach operation with a DH lower than 150 (FAA) ft (45m) but not lower than 100 ft (30m) and a runway visual range not less than 300m (1000 ft).
A-4
AC 20-191 Appendix A Term D efinition
• Category II A Type B instrument approach operation to a DH lower than 60 m (ICAO) (200 ft), but not lower than 30 m (100 ft) and a runway visual range not less than 300 m (1000 ft).
• Category III A precision instrument approach or approach and landing with a (FAA) decision height lower than 100 ft (30m), or no decision height, or a runway visual range less than 1000ft (300m).
• Category III A Type B instrument approach operation to a DH lower than 30 m (ICAO) (100 ft) or no DH and a runway visual range not less than 1000ft (300m) or no RVR limitations.
• Combiner The element of the head up display (HUD) in which the pilot simultaneously views the external visual scene along with synthetic information provided in symbolic form.
• Command Information that directs the pilot to follow a course of action in a Information specific situation (e.g., information provided by a flight director).
• Conformal Information that correctly overlays the image of the real world, Information irrespective of the pilot’s viewing position.
• Contaminated A runway is considered contaminated when more than 25 % of the Runway runway surface area (within reported length and width being used) is covered by standing water (greater than 1/8 inch or 3 mm), frost, ice, and any depth of snow, slush, or heavy rubber deposits.
• Decision A specified altitude in an instrument approach procedure at which the Altitude (DA) pilot must decide whether to initiate an immediate missed approach if the pilot does not see the required visual reference, or to continue the approach. Decision altitude is expressed in feet above mean sea level.
A-5
AC 20-191 Appendix A Term D efinition
• Decision For Category II and certain Category III procedures (e.g., when using Altitude a Fail Passive autoflight system), the DH (or an equivalent IM (Height) position fix) is the controlling minima, and the altitude value DA(H)) specified is advisory. The altitude value is available for cross reference. Use of a barometrically referenced DA for Category II is not currently authorized for 14 CFR Parts 121, 129, or 135 operations at U.S. facilities (Adapted from ICAO - IS&RP Annex 6).
• Decision A specified height above the ground in an instrument approach Height (DH) procedure at which the pilot must decide whether to initiate an immediate missed approach if the pilot does not see the required visual reference, or to continue the approach. Decision height is expressed in feet above ground level.
• Defined Path The path that is defined by the path definition function.
• Design Eye The three-dimensional volume in space surrounding the Design Eye Box Position from which the HUD information can be viewed.
• Design Eye The position at each pilot’s station from which a seated pilot achieves Position the optimum combination of outside visibility and instrument scan.
• Desired Path The path the flight crew and air traffic control can expect the aircraft to fly.
• Enhanced An installed aircraft system which uses an electronic means to Flight Vision provide a display of the forward external scene topography (the System natural or manmade features of a place or region especially in a way to show their relative positions and elevation) through the use of imaging sensors, including but not limited to forward-looking infrared, millimeter wave radiometry, millimeter wave radar, or lowlight level image intensification. An EFVS includes the display element, sensors, computers and power supplies, indications, and controls.
A-6
AC 20-191 Appendix A Term D efinition
• External Information the pilot derives from visual observation of real world Visual cues outside the cockpit.
Reference
• Extremely A probability of occurrence of 1 x 10-9 or less per hour of flight, or Improbable per event (e.g., takeoff, landing).
• Extremely A probability of occurrence between 1 x 10-9 and 1 x 10-7 per hour of Remote flight, or per event (e.g., takeoff, landing).
• Fail A system capable of completing the specified phases of an operation Operational following the failure of any single system component after passing a System point designated by the applicable safety analysis (e.g., Alert Height).
• Fail Passive A system that, in the event of a failure, causes no significant System deviation of aircraft flight path or attitude.
• Field of View As applied to a HUD, the angular extent of the display that can be seen from within the design eye box.
• Final The final bearing/radial/track of an instrument approach leading to a Approach runway, without regard to distance. For certain previously designed Course approach procedures that are not aligned with a runway, the FAC (FAC) bearing/radial/track of an instrument approach may lead to the extended runway centerline, rather than to alignment with the runway.
• Final The fix from which the final approach to an airport is executed. For Approach Fix standard procedures that do not involve multiple approach segments (FAF) intercepting the runway centerline near the runway, the FAF typically identifies the beginning of the straight-in final approach segment and the point where final segment descent may begin.
A-7
AC 20-191 Appendix A Term D efinition
• Final The segment of an approach extending from the Glide Path Intercept Approach Waypoint (GPIWP) or Approach Intercept Waypoint (APIWP), Segment whichever occurs later, to the Glide Path Intercept Reference Point (GIRP).
• Flight The means available to the flight crew to maneuver the aircraft in a Guidance specific manner either manually or automatically. It may include a System number of components such as the autopilot, flight directors, relevant display and annunciation elements and it typically accepts inputs from the airborne navigation system.
• Flight Path The FPAP is a point usually at or near the stop end of a runway. The Alignment point is used in conjunction with the Runway Datum Point (RDP) and Point (FPAP) a vector normal to the World Geological Survey – 1984 (WGS-84) ellipsoid at the RDP to define the geodesic plane of a final approach and landing flight path. The FPAP typically may be the RDP for the reciprocal runway.
• Flight Path The Flight Path Control Point (FPCP) is a calculated point located Control Point directly above the Runway Datum Point. The FPCP is used to relate (FPCP) the vertical descent of the final approach flight path to the landing runway.
• Flight The accuracy with which the aircraft is controlled as measured by the Technical indicated aircraft position with respect to the indicated command or Error (FTE) desired position. Note: FTE does not include human performance conceptual errors, typically that may be of large magnitude (e.g., entry of an incorrect waypoint or waypoint position, selection of an incorrect procedure, selection of an incorrect NAVAID frequency, failure to select a proper flight guidance mode).
• Frequent Occurring more often than 1 in 1000 events or 1000 flight hours.
A-8
AC 20-191 Appendix A Term D efinition
• GBAS A differential GNSS (e.g., GPS)-based landing system providing both Landing vertical and lateral position fixing capability. Note: Term may be System applied to any GNSS based differentially corrected landing system (GLS) providing lateral and vertical service for approach and landing equivalent to or better than that provided by a U.S. Type I ILS, or equivalent ILS specified by ICAO Annex 10.
• Glide Path A descent profile determined for vertical guidance during a final (GP) approach.
• Glide Path The glide path angle is an angle defined at the FPCP that establishes Angle (GPA) the descent gradient for the final approach flight path of an approach procedure. It is measured in the geodesic plane of the approach (defined by the RDP, FPAP, and WGS-84 ellipsoid’s center). The vertical and horizontal references for the GPA are a vector normal to the WGS-84 ellipsoid at the RDP and a plane perpendicular to that vector at the FPCP, respectively.
• Glide Path The point at which the extension of the final approach path intercepts Intercept the runway.
Reference Point (GIRP)
• Glide Path The point at which the established glide slope intercept altitude Intercept (MSL) meets the Final Approach Segment (FAS), on a standard day, Waypoint using a standard altimeter setting (1013.2 HPa or 29.92 in).
(GPIWP)
• Glideslope Part of the ILS that projects a radio beam upward at an angle of (GS) approximately three degrees from the approach end of an instrument runway. The glideslope (GS) provides vertical guidance to aircraft on the final approach course for the aircraft to follow when making an ILS approach along the Localizer (LOC) path.
A-9
AC 20-191 Appendix A Term D efinition
• Global A world-wide position, velocity, and time determination system that Navigation uses one or more satellite constellations.
Satellite System (GNSS)
• Global The NAVSTAR Global Positioning System operated by the United Positioning States Department of Defense (DOD). It is a satellite-based radio System navigation system composed of space, control, and user segments.
(GPS) The space segment is composed of satellites. The control segment is composed of monitor stations, ground antennas, and a master control station. The user segment consists of antennas and receiverprocessors that derive time and compute a position and velocity from the data transmitted from the satellites.
• Go-Around A transition from an approach to a stabilized climb.
• Guidance Information used during manual control or monitoring of automatic control of the aircraft that is of sufficient quality to be used by itself for the intended purpose.
• Head Up A display with the following characteristics:
Display • A head-up presentation not requiring the transition of visual(HUD) attention from head down to head up,System
• displays imagery and or/symbology conformal (as defined in SAE AS 8055) with the pilot’s external view,
• permits simultaneous view of the imagery (if presented), aircraft flight symbology and the external view, and
• display characteristics and dynamics are suitable for manual control of the aircraft.
• Hybrid A combination of two, or more, systems of dissimilar design used to System perform a particular operation.
A-10
AC 20-191 Appendix A Term D efinition
• ICAO Type An instrument approach operation to a DH below 75m (250 ft) Type B Instrument B instrument approach operations are further categorized as Category Approach I, II, and III defined above.
• Improbable -9 A probability of occurrence greater than 1 x 10 but less than or -5 equal to 1 x 10 per hour of flig ht, or per event (e.g., takeoff, landing).
• Independent A system that is not adversely influenced by the operation, Systems computation, or failure of some other identical, related, or separate system (e.g., two separate ILS receivers).
• Infrequent Occurring less often than 1 in 1000 events or 1000 flight hours.
• Instantaneous The angular extent of a HUD display that can be seen from either eye Field of View from a fixed position of the head.
• Integrity A measure of the acceptability of a system, or system element, to contribute to the required safety of an operation.
• Landing For the purpose of this AC, landing begins at 100 ft., the DH or the AH and ends at the first contact of the wheels for fixed wing aircraft with the runway.
• Landing For the purpose of this AC, rollout starts from the first contact of the rollout wheels with the runway and finishes when the aircraft has slowed to a safe taxi speed (in the order of 30 knots).
• Missed The flight path followed by an aircraft after discontinuation of an Approach approach procedure and initiation of a go-around. Typically, a “missed approach” follows a published missed approach segment of an IAP, or follows radar vectors to a MAP, return to landing, or diversion to an alternate.
A-11
AC 20-191 Appendix A Term De finition
• Monitored A HUD that has internal or external capability to reliably detect HUD erroneous sensor inputs or guidance outputs, to assure that a pilot does not receive incorrect or misleading guidance, failure, or status information.
• Non-Normal Conditions or configurations of the aircraft that would not normally Conditions be experienced during routine flight operations usually due to failures
(e.g., engine failure, electrical failure, autothrottle/autothrust failure, etc.).
• NOTAM Notice to Airmen - A notice distributed by means of telecommunication containing information concerning the establishment, condition, or change in any aeronautical facility, service, procedure or hazard, the timely knowledge of which is essential to personnel concerned with flight operations. (ICAO - IS&RP Annex 6).
• Performance A measure of the accuracy with which an aircraft, a system, or an element of a system operates compared against specified parameters.
Performance demonstration(s) typically include the component of FTE.
• Rare Normal A condition which must be expected to normally occur, but does so Conditions only very infrequently (e.g., unusually strong winds, significant wind gradients, significant turbulence, significant in-flight icing, significant mountain wave activity).
• Redundant The presence of more than one independent means for accomplishing a given function or flight operation. Each means need not necessarily be identical.
A-12
AC 20-191 Appendix A Term D efinition
• Rejected A discontinued landing attempt. A rejected landing is typically Landing initiated at low altitude, but prior to touchdown. If from or following an instrument approach, a rejected landing typically is considered to be initiated below DA(H) or MDA(H). A rejected landing may be initiated in either Visual Meteorological Conditions (VMC) or Instrument Meteorological Conditions (IMC). A rejected landing typically leads to or results in a go-around and if following an instrument approach, a “Missed Approach.” If related to consideration of aircraft configuration(s) or performance, it is sometimes referred to as a “Balked Landing.” The term “rejected landing” is used to be consistent with regulatory references such as found in 14 CFR 121, appendix E, and policy references as in FAA Order 8400.10.
• Remote A probability of occurrence greater than 1 x 10-7 but less than or equal to 1 x 10-5 per hour of flight, or per event (e.g., takeoff, landing).
• Required That section of the visual aids or of the approach area that should Visual have been in view for sufficient time for the pilot to make an Reference assessment of the aircraft’s position and rate of change of position, in relation to the desired flight path. In Category III operations with a DH, the required visual reference is that specified for the particular procedure and operations (ICAO - IS&RP Annex 6 - DH definition - Note 2).
• Runway The RDP is used in conjunction with the FPAP and a vector normal Datum Point to the WGS-84 ellipsoid at the RDP. The RDP defines the geodesic (RDP) plane of a final approach flight path to the runway for touchdown and rollout. It is a point at the designated lateral center of the landing runway defined by latitude, longitude, and ellipsoidal height. The RDP is typically a surveyed reference point used to connect the approach flight path with the runway. The RDP may or may not The RDP may or may not necessarily be coincident with the designated runway necessarily be coincident with the designated runway threshold.
A-13
AC 20-191 Appendix A Term D efinition
• Runway That segment of an approach from the glidepath intercept reference Segment point (GIRP) to Flight Path Alignment Point (FPAP).
(RWS)
• Safe An approach that does not penetrate the Obstacle Limitation Surfaces Approach for Precision Approach Category II or III as defined by ICAO SARPs Annex 14 Section 4.2.15 and Table 4-1.
• Safe Landing Landing in the touchdown landing box which includes longitudinally between 200 ft and 3000 ft. or the end of the touchdown zone, and laterally from with the outbound landing gear within 70 ft. from the runway centerline.
• Safe Taxi The speed at which the pilot can safely leave the runway or bring the Speed aircraft to a safe stop.
• Standard In the context of this section of this AC, is a navigation service Landing Aid provided by a State that meets internationally accepted performance (SLA) standards (e.g., ICAO Standards and Recommended Practices (SARP’s) or equivalent State standards).
• Synthetic Information provided to the flight crew by instrumentation or Reference electronic displays. May be either command or situation information.
• Synthetic A guidance system which integrates a synthetic vision system scene Vision depiction with additional functionality that includes a flight path Guidance vector and flight path angle reference cue, and display elements that System include runway of intended landing to support operations below (SVGS) standard precision approach operating minima.
• Takeoff Takeoff guidance system includes position sensors, displays, Guidance indicators and controls as a minimum. The takeoff guidance system System provides directional command guidance to the pilot during a takeoff, or takeoff and rejected takeoff phase of flight.
A-14