AC 120-28D Appendix 1 07/13/99 Extended Final Approach Segment (EFAS) That segment of an approach, co-linear with the Final Approach Segment, but which extends beyond the Glidepath Intercept Waypoint (GPIWP) or Approach Intercept Waypoint (APIWP).
External Visual Reference Information the pilot derives from visual observation of real world cues outside the cockpit.
Extremely Improbable A probability of occurrence on the order of 1 x 10 -9 or less per hour of flight, or per event (e.g., takeoff, landing).
Extremely Remote A probability of occurrence between the orders of 1 x 10 -9 and 1 x 10-7 per hour of flight, or per event (e.g., takeoff, landing).
Fail Operational System A system capable of completing the specified phases of an operation following the failure of any single system component after passing a point designated by the applicable safety analysis (e.g., Alert Height).
Fail Passive System A system which, in the event of a failure, causes no significant deviation of aircraft flight path or attitude.
Field of View As applied to a Head Up Display - the angular extent of the display that can be seen from within the design eye box.
Frequent Occurring more often than 1 in 1000 events or 1000 flight hours.
Final Approach Course (FAC) The final bearing/radial/track of an instrument approach leading to a runway, without regard to distance. For certain previously designed approach procedures that are not aligned with a runway, the FAC bearing/radial/track of an instrument approach may lead to the extended runway centerline, rather than to alignment with the runway.
Final Approach Fix (FAF) The fix from which the final approach to an airport is executed. For standard procedures that do not involve multiple approaches segments intercepting the runway centerline near the runway, the FAF typically identifies the beginning of the straight-in final approach segment.
Final Approach Point (FAP) The point applicable to instrument approaches other than ILS, MLS or GLS, with no depicted FAF (e.g., only applies to approaches such as an on-airport VOR or NDB), where the aircraft is established inbound on the final approach course from a procedure turn, and where descent to the next procedurally specified altitude, or to minimum altitude, may be commenced.
Final Approach Segment (FAS) The segment of an approach extending from the Glidepath Intercept Waypoint (GPIWP) or Approach Intercept Waypoint (APIWP), whichever occurs later, to the Glidepath Intercept Reference Point (GIRP).
Flight Guidance System The means available to the flightcrew to maneuver the aircraft in a specific manner either manually or automatically. It may include a number of components such as the autopilot, flight directors, relevant display and annunciation elements and it typically accepts inputs from the airborne navigation system.
AC 120-28D 07/13/99 Appendix 1 Flight Path Alignment Point (FPAP) The FPAP is a point, usually at or near the stop end of a runway, used in conjunction with the RDP and a vector normal to the 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 Control Point (FPCP) The Flight Path Control Point (FPCP) is a calculated point located directly above the Runway Datum Point. The FPCP is used to relate the vertical descent of the final approach flight path to the landing runway.
Flight Technical Error (FTE) The accuracy with which the aircraft is controlled as measured by the indicated aircraft position with respect to the indicated command or desired position. Note: FTE does not include human performance conceptual errors, typically which 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).
Glide Path Angle [GPA] The glide path angle is an angle, defined at the FPCP, that establishes 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 Intercept Waypoint (GPIWP) The point at which the established glide slope intercept altitude (MSL) meets the Final Approach Segment (FAS), on a standard day, using a standard altimeter setting (1013.2 HPa or 29.92 in).
Glidepath Intercept Reference Point [GIRP] The Glidepath Intercept Reference Point is the point at which the extension of the final approach path intercepts the runway.
GNSS Landing System (GLS) A differential GNSS (e.g., GPS) based landing system providing both vertical and lateral position fixing capability. Note: Term may be applied to any GNSS based differentially corrected landing system 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.
Global Positioning System [GPS] The NAVSTAR Global Positioning System operated by the United States Department of Defense. It is a satellite -based radio navigation system composed of space, control and user segments. 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 receiver-processors that derive time and compute a position and velocity from the data transmitted from the satellites.
Global Navigation Satellite System [GNSS] A world wide position, velocity and time determination system that uses one or more satellite constellations.
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.
AC 120-28D Appendix 1 07/13/99 Go-around A transition from an approach to a stabilized climb.
Hazardous Failure Condition Failure Conditions which would reduce the capability of the airplane or the ability of the crew to cope with adverse operating conditions to the extent that there would be:
(i) A large reduction in safety margins or functional capabilities;
(ii) Physical distress or higher workload such that the flightcrew cannot be relied upon to perform their tasks accurately or completely; or
(iii) Serious or fatal injury to a relatively small number of the occupants.
Head Up Display System An aircraft system which provides head-up guidance to the pilot during flight.
It includes the display element, sensors, computers and power supplies, indications and controls. It may receive inputs from an airborne navigation system or flight guidance system.
Hybrid System A combination of two, or more, systems of dissimilar design used to perform a particular operation.
Improbable A probability of occurrence greater than 1 x 10 -9 but less than or equal to 1 x 10-5 per hour of flight, or per event (e.g., takeoff, landing).
Independent Systems A system that is not adversely influenced by the operation, 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.
Initial Missed Approach (IMAWP) Waypoint used to define the Missed Approach Point (MAP).
Initial Missed Approach Segment That segment of an approach from the Glide Path Intercept Waypoint (GPIWP) to the Initial Missed Approach Waypoint (IMAWP).
Instantaneous Field of View The angular extent of a HUD display which can be seen from either eye 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 will begin at 100 ft., the DH or the AH to the first contact of the wheels with the runway.
Landing rollout For the purpose of this AC, rollout starts from the first contact of the wheels with the runway and finishes when the airplane has slowed to a safe taxi speed (in the order of 30 knots).
Major Failure Condition Failure Condition which would reduce the capability of the airplane or the ability of the crew to cope with adverse operating conditions to the extent
AC 120-28D 07/13/99 Appendix 1 that there would be, for example, a significant reduction in safety margins or functional capabilities, a significant increase in crew workload or in conditions impairing crew efficiency, or discomfort to occupants, possibly including injuries.
Minimum Descent Altitude(Height) [MDA(H)] See individual definitions below for MDA and MDH.
Minimum Descent Altitude (MDA) A specified altitude in a non-precision approach or circling approach below which descent must not be made without the required visual reference.
Minimum Descent Altitude (MDA) is referenced to mean sea level.
(ICAO - IS&RP Annex 6).
Minimum Descent Height (MDH) A specified height in a non-precision approach or circling approach below which descent must not be made without the required visual reference.
Minimum Descent Height (MDH) is referenced to aerodrome elevation or to the threshold if that is more than 7 ft. (2m) below the aerodrome elevation.
A MDH for a circling approach is referenced to the aerodrome elevation.
(ICAO - IS&RP Annex 6).
FAA Note - The United States does not use Minimum Descent Heights.
Minimum Use Height (MUH) A height specified during airworthiness demonstration or review above which, under standard or specified conditions, a probable failures of a system is not likely to cause a significant path displacement unacceptably reducing flight path clearance from specified reference surfaces (e.g., airport elevation) or specified obstacle clearance surfaces.
Minor Failure Condition Failure Condition which would not significantly reduce airplane safety and which involve crew actions that are well within their capabilities. Minor Failure Conditions may include, for example, a slight reduction in safety margins or functional capabilities, a slight increase in crew workload, such as routine flight plan changes, or some inconvenience to occupants.
Missed Approach The flight path followed by an aircraft after discontinuation of an approach procedure and initiation of a go-around. Typically a “missed approach” follows a published missed approach segment of an instrument approach procedure, or follows radar vectors to a missed approach point, return to landing, or diversion to an alternate.
Monitored HUD A HUD which has internal or external capability to reliably detect erroneous sensor inputs or guidance outputs, to assure that a pilot does not receive incorrect or misleading guidance, failure, or status information.
Non-Normal Means of Navigation A means of navigation which does not satisfy one or more of the necessary levels of accuracy, integrity, and availability for a particular area, route, procedure or operation, and which may require use of a pilot's "emergency authority" to continue navigation.
NOTAM Notice to Airmen - A notice distributed by means of telecommunication containing information concerning the establishment, condition or change in
AC 120-28D Appendix 1 07/13/99 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 Flight Technical Error (FTE).
Primary Means of Navigation A means of navigation which satisfies the necessary levels of accuracy and integrity for a particular area, route, procedure or operation. The failure of a "Primary Means" of navigation may result in, or require reversion to a "nonnormal" means of navigation, or an alternate level of RNP.
NOTE: Qualification as a "primary means" of navigation typically requires that ANP/EPU be less than RNP for 99.99% of the time.
Redundant The presence of more than one independent means for accomplishing a given function or flight operation. Each means need not necessarily be identical.
Rejected Landing A discontinued landing attempt. A rejected landing typically is initiated at low altitude, but prior to touchdown. If from or following an instrument approach it typically is considered to be initiated below DA(H) or MDA(H).
A rejected landing may be initiated in either VMC or 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 sometime referred to as a "Balked Landing." The term "rejected landing is used to be consistent with regulatory references such as found in FAR121 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 Navigation Performance (RNP) A statement of the navigation performance necessary for operation within a defined airspace (Adapted from ICAO - IS&RP Annex 6).
NOTE: Required Navigation Performance is specified in terms of accuracy, integrity, and availability of navigation signals and equipment for a particular airspace, route, procedure or operation.
Required Navigation Performance Containment (RNP Containment) RNP Containment represents a bound of the rare-normal performance and specified non-normal performance of a system, typically expressed as 2*RNP(X).
When RNP represents Gaussian statistical performance at a level of two sigma (2 x standard deviation), then containment represents a nominal performance bound specified at the level of four sigma (4 x standard deviation). Note: RNP containment use may vary with intended operational applications.
Required Navigation Performance Level or Type (RNP Level or RNP Type) A value typically expressed as a distance in nautical miles from the intended position within which an aircraft would be for at least 95 percent of the total flying time (Adapted from ICAO - IS&RP Annex 6).
AC 120-28D 07/13/99 Appendix 1 NOTE: Applications of RNP to terminal area and other operations may also include a vertical and/or longitudinal component. ICAO may use the term RNP Type, while certain other States, aircraft manuals, procedures, and operators may use the term RNP Level.
Example - RNP 4 represents a navigation lateral accuracy of plus or minus 4 nm (7.4 km) on a 95% basis. RNP is typically defined in terms of its lateral accuracy, and has an associated lateral containment boundary.
Required Visual Reference That section of the visual aids or of the approach area which should have been in view for sufficient time for the pilots to have made an 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 decision height, the required visual reference is that specified for the particular procedure and operations (ICAO - IS&RP Annex 6 - Decision Height definition - Note 2).
Runway Datum Point (RDP) The RDP is used in conjunction with the FPAP and a vector normal to the WGS-84 ellipsoid at the RDP to define the geodesic 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 necessarily be coincident with the designated runway threshold Runway Segment (RWS) That segment of an approach from the glidepath intercept reference point (GIRP) to Flight Path Alignment Point (FPAP).
Situation Information Information that directly informs the pilot about the status of the aircraft system operation or specific flight parameters including flight path.
Standard Landing Aid (SLA) In the context of this section of this AC, is a navigation service provided by a State which meets internationally accepted performance standards (e.g., ICAO Standards and Recommended Practices (SARP’s) or equivalent State standards).
Supplementary Means of Navigation A means of navigation which satisfies one or more of the necessary levels of accuracy, integrity, or availability for a particular area, route, procedure or operation. The failure of a "Supplementary Means" of navigation may result in, or require reversion to another alternate "normal" means of navigation for the intended route, procedure or operation.
NOTE: Qualification as a "supplementary means" of navigation typically requires that ANP/EPU be less than RNP for 99% of the time.
Synthetic Reference Information provided to the crew by instrumentation or electronic displays.May be either command or situation information.
Synthetic Vision System A system used to create a synthetic image representing the environment external to the airplane.
Take off Guidance System A system which provides directional command guidance to the pilot during a takeoff, or takeoff and aborted takeoff. It includes sensors, computers and power supplies, indications and controls.
AC 120-28D Appendix 1 07/13/99 Total Field of View The maximum angular extent of the display that can be seen with either eye, allowing head motion within the design eye box.
Touch Down Zone (TDZ) The first 3000 ft. of usable runway for landing, unless otherwise specified by the FAA, or other applicable ICAO or State authority (e.g., for STOL aircraft, or in accordance with an SFAR).
Visual Guidance Visual information the pilot derives from the observation of real world cues, outside the cockpit and uses as the primary reference for aircraft control or flight path assessment.
AC 120-28D 07/13/99 Appendix 1 Acronyms.
ACRONYM EXPANSION ABAS Aircraft Based Augmentation System AC Advisory Circular ACI Adjacent Channel Interface ADF Automatic Direction Finder ADI Attitude Director Indicator ADS Automatic Dependent Surveillance AFCS Autopilot Flight Control System AFDS Autopilot Flight Director System AFGS Automatic Flight Guidance System AFM Airplane Flight Manual AH Alert Height AHI All-Weather Harmonization Items AIP Aeronautical Information Publication ALS Approach Light System ANP Actual Navigation Performance APIWP Approach Intercept Waypoint APM Aircrew Program Manager APU Auxiliary Power Unit AQP Advanced Qualification Program ARA Airborne Radar Approach ASR Airport Surveillance Radar ATC Air Traffic Control ATIS Automatic Terminal Information Service ATOGW Allowable Takeoff Gross Weight ATPC Airline Transport Pilot Certificate ATS Air Traffic Service AWO All Weather Operations BARO [Abbreviation for "Barometric"] BC Back Course (e.g., ILS Back Course) BITE Built-In Test Equipment CAA Civil Aviation Authority CDL Configuration Deviation List CFR Code of Federal Regulations CFR Crash Fire Rescue
AC 120-28D Appendix 1 07/13/99 CHDO Certificate Holding District Office CMO [FAA] Certificate Management Office CMU [FAA] Certificate Management Unit CL Centerline Lights CNS Communication, Navigation and Surveillance CRM Collision Risk Model CRM Cockpit Resource Management CVR Cockpit Voice Recorder DA Decision Altitude DA(H) Decision Altitude(Height) DCH Datum Crossing Height DD DME-DME updating DDM Difference of Depth Modulation DEP Design Eye Position DGNSS Differential Global Navigation Satellite System DH Decision Height DME Distance Measuring Equipment DOD [U.S.] Department of Defense DOT [U.S.] Department of Transportation DP Departure Procedure EADI Electronic Attitude Director Indicator ECEF Earth Centered Earth Fixed EFAS Extended Final Approach Segment EGPWS Enhanced Ground Proximity Warning System EHSI Electronic Horizontal Situation Indicator EPE Estimated Position Error EPU Estimated Position Uncertainty EROPS Extended Range Operations (any number of engines) ET Elapsed Time ET Error Term [FMS use] ETOPS Extended Range Operations with Two-Engine Airplanes EVS Enhanced Vision System FAF Final Approach Fix FAP Final Approach Point FAR Federal Aviation Regulation FAS Final Approach Segment
AC 120-28D 07/13/99 Appendix 1 FBS Fixed Base Simulator FBW Fly-by-wire FCOM Flight Crew Operating Manual FDR Flight Data Recorder FGS Flight Guidance System FHA Functional Hazard Assessment FLIR Forward Looking Infrared Sensor FM Frequency Modulation FM Fan Marker FMC Flight Management Computer FMS Flight Management System FPAP Flight Path Alignment Point FPA Flight Path Angle FPCP Flight Path Control Point FSB Flight Standardization Board FSDO [FAA] Flight Standards District Office FSS [FAA] Flight Service Station FTE Flight Technical Error GA Go-Around GBAS Ground Based Augmentation System GCA Ground Controlled Approach GIRP Glidepath Intercept Reference Point GLS GPS (or GNSS) Landing System GNSS Global Navigation Satellite System GPA Glide Path Angle GPIWP Glide Path Intercept Waypoint GPWS Ground Proximity Warning System GPS Global Positioning System HAA Height Above Airport HAT Height above Touchdown HDG Heading HQRS Handling Quality Rating System (see AC 25-7A, as amended) HUD Head Up Display IAP Instrument Approach Procedure IAW In Accordance With ICAO International Civil Aviation Organization
AC 120-28D Appendix 1 07/13/99 IFR Instrument Flight Rules IM Inner Marker IMAS Initial Missed Approach Segment IMAWP Initial Missed Approach Waypoint IMC Instrument Meteorological Conditions ILS Instrument Landing System INAS International Airspace System IOE Initial Operating Experience IRS Inertial Reference System IRU Inertial Reference Unit JAA Joint Aviation Authority JAR AWO Joint Aviation Regulations – All Weather Operations KRM [Type of Landing system used in certain foreign States] LAAS Local Area Augmentation System LAD Local Area Differential LAHSO Land And Hold Short Operation LDA Localizer Descent Aid [approach type] LLM Lower Landing Minima LMM Compass Locator Middle Marker LLTV Low Light Level TV LNAV Lateral Navigation LOC [ILS] Localizer LOE Line operational evaluation LOFT Line oriented flight training LOM Compass Locator Outer Marker LOS Line oriented simulation MAP Mode Annunciator Panel MAP Missed Approach Point MASPS Minimum Aviation System Performance Standards MB Marker Beacon MCP Mode Control Panel MDA Minimum Descent Altitude MDA(H) Minimum Descent Altitude(Height) MDH Minimum Descent Height - NOTE: MDH is not used for U.S. Operations MEH Minimum Engage Height MEL Minimum Equipment List
AC 120-28D 07/13/99 Appendix 1 METAR ICAO Routine Aviation Weather Report MLS Microwave Landing System MM Middle Marker MMEL Master Minimum Equipment List MMR Multi-mode Receiver MOT Ministry of Transport MRB Maintenance Review Board MSL Mean Sea Level [altitude reference datum] MUH Minimum Use Height MVA Minimum Vectoring Altitude NA Not Authorized or Not Applicable NAS National Airspace System NAVAID Navigational Aid ND Navigation Display NDB Navigation Data Base NDB Non-directional Beacon NOTAM Notice to Airman NRS National Resource Specialist OCA Obstacle Clearance Altitude OCH Obstacle Clearance Height OCL Obstacle Clearance Limit OIS Obstacle Identification Surface OM Outer Marker OSAP Offshore Standard Approach Procedure PAI Principal Avionics Inspector PAR Precision Approach Radar PC/PT Proficiency Check/Proficiency Training PF Pilot Flying PFC Porous Friction Coarse [runway surface] PIC Pilot in Command PIREP Pilot Weather Report PNF Pilot Not Flying POC Proof of Concept POI Principal Operations Inspector PMI Principal Maintenance Inspector PRD Progressive Re-Dispatch