Glossary Flashcards
1
Q
Advisory Route
A
A designated route along which Air Traffic Advisory Service is available. (EU 923/2012)
2
Q
Aerodrome
A
A defined area (including any buildings, installations and equipment) on land or water or on a fixed, off-shore or floating structure intended to be used either wholly or in part for the arrival, departure and surface movement of aircraft.
3
Q
Aerodrome Control Service
A
Air Traffic Control service for aerodrome traffic.
4
Q
Aerodrome Control Tower
A
A unit established to provide air traffic control services to aerodrome traffic.
5
Q
Aerodrome Traffic
A
All traffic on the manoeuvring area of an aerodrome and all aircraft flying in the vicinity of an aerodrome. An aircraft operating in the vicinity of an aerodrome includes but is not limited to aircraft entering or leaving an aerodrome traffic circuit.
6
Q
Aerodrome Traffic Circuit
A
The specific path to be flown by aircraft operating in the vicinity of an aerodrome.
7
Q
Aerodrome Traffic Zone
A
Airspace of defined dimensions established around an aerodrome for the protection of aerodrome traffic.
8
Q
Aircraft
A
Any machine that can derive support in the atmosphere from the reactions of the air other than the reactions of the air against the earths surface.
9
Q
Aircraft Identification
A
A group of letters, figures or a combination thereof which is either identical to, or the coded equivalent of, the aircraft call sign to be used in air-ground communications, and which is used to identify the aircraft in ground-ground air traffic services communications.
10
Q
Air-Ground Communication
A
Two way communication between aircraft and stations or locations on the surface of the earth.
11
Q
Air Navigation Service Provider
A
An organisation having applied for a certificate to provide such services.
12
Q
Air-Taxiing
A
The movement of a helicopter/VTOL above the surface of an aerodrome, normally in ground effect and at a ground speed normally less than 37 kph.
13
Q
Air Traffic
A
All aircraft in flight or operating on the manoeuvring area of an aerodrome.
14
Q
Air Traffic Advisory Service
A
A service provided within advisory airspace to ensure separation, in so far as is practical, between aircraft which are operating on IFR flight plans.
15
Q
Air Traffic Control Clearance
A
Authorisation for an aircraft to proceed under conditions specified by an Air Traffic Control unit.
16
Q
Air Traffic Control Instruction
A
Directives issued by air traffic control for the purpose of requiring a pilot to take specific action.
17
Q
Air Traffic Control Service
A
A service provided for the purpose of preventing collisions between aircraft, and on the manoeuvring area between aircraft and obstructions; and expediting and maintaining an orderly flow of traffic.
18
Q
Air Traffic Control Unit
A
A generic term meaning variously, area control centre, approach control unit or aerodrome tower.
19
Q
Air Traffic Flow Management
A
A service established with the objective of contributing to a safe, orderly and expeditious flow of air traffic by ensuring that ATC capacity is utilised to the maximum extent possible, and that the traffic volume is compatible with the capacities declared by the appropriate ATS authority.
20
Q
Air Traffic Management
A
The aggregation of the airborne and ground based functions (air traffic services, airspace management and air traffic flow management) required to ensure the safe and efficient movement of aircraft during all phases of operations.
21
Q
Air Traffic Service
A
A generic term meaning variously, flight information service, alerting service, air traffic advisory service, air traffic control service (area control service, approach control service or aerodrome control service).
22
Q
Airway
A
A control area or portion thereof established in the form of a corridor.
23
Q
Alerting Service
A
A service provided to notify appropriate organisations regarding aircraft in need of search and rescue aid, and assist such organisations as required.
24
Q
Alternate Aerodrome
A
An aerodrome to which an aircraft may proceed when it becomes either impossible or inadvisable to proceed to or land at the aerodrome of intended landing.
25
Altitude
The vertical distance of a level, a point or an object considered as a point, measured from Mean Sea Level.
26
Approach Control Service
Air traffic control service for arriving or departing controlled flight.
27
Approach Control Unit
A unit established to provide air traffic control service to controlled flights arriving at, or departing from, one or more aerodromes.
28
Approach Procedure
An instrument procedure which utilises lateral and vertical guidance but does not meet the requirements for precision approach and landing operations.
29
Approach Sequence
The order in which two or more aircraft are cleared to approach to land at the aerodrome.
30
Approval Request
A request for clearance made by an ACC when an aircraft will be entering the controlled or advisory airspace of an adjacent ACC in less than 15 minutes, and the first designated reporting point is in the adjacent area.
31
Approved Departure Time
An allocated take off time calculated from the elapsed flight time between the aerodrome of departure and the point at which the regulated flow is effective.
32
Apron
A defined area, intended to accommodate aircraft for the purpose of loading or unloading passengers, mail or cargo, fuelling, parking or maintenance.
33
Area Control Centre
An Air Traffic Control unit established to provide an air traffic control service to controlled flights in control areas under its jurisdiction.
34
Area Control Service
An Air Traffic Control service for controlled flights in controlled areas.
35
Area Navigation (RNAV)
A method of navigating which permits aircraft operations 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.
36
Arrival Routes
Routes identified in an instrument approach procedure by which aircraft may proceed from the en route phase of flight to an initial approach fix.
37
ATC Unit Terrain Safe Level
The applicable level as published in ATC unit procedures, that ensures IFR terrain clearance requirements.
38
ATS Route
A specified route designed for channeling the flow of traffic as necessary for the provision of air traffic services.
39
ATS Surveillance Service
Term used to indicate a service provided directly by means of an ATS surveillance system.
40
ATS Surveillance System
A generic term meaning variously, ADS-B, PSR, SSR or any comparable ground based system that enables the identification of aircraft. A comparable ground based system is one that has demonstrated, by comparative assessment or other methodology, to have a level of safety and performance equal to or better than mono pulse SSR.
41
Automatic Dependant Surveillance
A means by which aircraft, aerodrome vehicles and other objects can automatically transmit and/or receive data such as identification, position and additional data, as appropriate, in a broadcast via a data link.
42
Automatic Terminal Information Service (ATIS)
The automatic provision of current, routine information to arriving and departing aircraft throughout 24 hours or a specified portion thereof. (Note: either via data link or repetitive voice broadcasts).
43
Base Turn
A turn executed by an aircraft during the initial approach between the end of the outbound track and the beginning of the intermediate or final approach track. These tracks are not reciprocal.
44
Ceiling
The height above ground or water of the base of the lowest layer of cloud below 20,000ft covering more than half the sky.
45
Clearance Limit
The point to which an aircraft is granted air traffic control clearance.
46
Clearway
An area at the end of the take-off run available, selected or prepared as a suitable area over which an aircraft may make a portion of its climb to a specified height.
47
Contact Point
The position, time or level at which an arriving aircraft is to establish communication with approach control.
48
Control Area
Controlled airspace extending upwards from a specified limit above the earth.
49
Control Zone
Controlled airspace extending upwards from the surface of the earth to a specified upper limit.
50
Controlled airspace
Airspace of defined dimensions within which air traffic control service is provided in accordance with the airspace classification.
51
Controlled Flight
Any flight which is subject to an air traffic control clearance.
52
Controller
A generic term encompassing: civil and MOD air traffic controllers, ASACS weapons controllers, and any other military personnel who are trained, authorised and certified to provide some or all of the suite of services that compromise UK FIS.
53
Controller Overload
An ATC situation during which a controller considers he experienced excessive workload to a point where the safety of aircraft under his control was, or could have been, compromised.
54
Controller-Pilot Data Link Communications
A means of communication between controller and pilot, using data link for ATC communications.
55
Co-ordination
The act of negotiation between two or more parties each vested with the authority to make executive decisions appropriate to the task being discharged.
56
Cruising Level
A level maintained during a significant portion of a flight.
57
Current Flight Plan
The flight plan, including changes, if any, brought about by subsequent clearances.
58
Decision Height
In relation to the operation of an aircraft at an aerodrome means the height in a precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been established.
59
Declared Capacity
A measure of the ability of the ATC system or any of its subsystems or operating positions to provide service to aircraft during normal activities. It is expressed as the number of aircraft entering a specified portion of airspace in a given period of time, taking due account of weather, ATC unit configuration, staff and equipment available, and any other factors which may affect the workload of the controller responsible for the airspace.
60
Deconfliction Advice
Advice issued by a controller to pilots, aimed at achieving notified deconfliction minima from other traffic in Class F/G airspace.
61
Deconfliction Instruction
Instruction issued by a controller to pilots in receipt of a Procedural Service, which if complied with shall achieve deconfliction minima against other aircraft participating in the Procedural Service.
62
Deconfliction Minima
The defined vertical, lateral or time minima relevant to the provision of UK Flight Information Services.
63
Elevation
The vertical distance of a point or level on, or affixed to, the surface of the earth measured from Mean Sea Level.
64
En-Route Operations
Operations conducted on published ATS routes, direct point-to-point operations between defined waypoints, or along great circle routes which are other than take off, landing, departure, arrival or terminal operations.
65
Entry Point
The first airways/advisory airspace reporting point over which a flight passes on entering an FIR.
66
Exit Point
The last airways/advisory airspace reporting point over which a flight passes before leaving an FIR.
67
Expected Approach Time
The time at which an ATC expects that an arriving aircraft, following a delay, will leave the holding fix to complete its approach for landing. The actual time of leaving the holding fix will depend upon the approach clearance.
68
Estimated of Block Time
The estimated time at which the aircraft will commence movement associated with departure.
69
Estimated Time of Arrival
For IFR flights, the time at which it is estimated that the aircraft will arrive over that designated point, defined by reference to navigation aids, from which it is intended that an instrument approach procedure will be commenced, or, if no navigation aid is associated with the aerodrome, the time at which the aircraft will arrive over the aerodrome. For VFR flights, the time at which it is estimated that the aircraft will arrive over the aerodrome.
70
Final Approach
That part of an instrument approach which commences at the specified final approach fix or point.
71
Flight Information Service
A service provided for the purpose of giving advice and information useful for the safe and efficient conduct of flights.
72
Flight Level
A surface of constant atmospheric pressure, which is related to a specific pressure datum, 1013.25 hPa, and is separated from other such surfaces by specific pressure intervals.
73
Flight Path Monitoring
The use of ATS surveillance systems for the purpose of providing aircraft with information and advice relative to significant deviations from nominal flight path, including deviations from the terms of their ATC clearance.
74
Flight Plan
Specified information provided to air traffic service units relative to an intended flight or portion of a flight of an aircraft.
75
Flight Visibility
The visibility forward from the cockpit of an aircraft in flight.
76
General Air Traffic Flights
Conducted in accordance with the Regulations and Procedures for flight promulgated by the State Civil Aviation Authorities and operating under the control or authority of the Civil ATS organisation.
77
Ground Visibility
The visibility at an aerodrome, as reported by an accredited observer or by automatic systems.
78
Heading
The direction in which the longitudinal axis of an aircraft is pointed, usually expressed in degrees from North (true, magnetic or compass).
79
Height
The vertical distance of a level, a point or an object considered as a point, measured from a specified datum.
80
Holding Point
Either:
- a specified location, identified by visual or other means, in the vicinity of which the position of an aircraft in flight is maintained in accordance with air traffic control clearances.
- a speech abbreviation used in radiotelephony phraseology having the same meaning as Runway Holding Position or Intermediate Holding Position as defined in CAP 168 Licensing of Aerodromes.
81
Holding Procedure
A predetermined manoeuvre which keeps an aircraft within a specified airspace whilst awaiting further clearance.
82
Hot Spot
A location on an aerodrome movement area with a history or potential risk of collision or runway incursion, and where heightened attention by pilots/drivers is necessary.
83
Identification
The situation which exists when the position indication of a particular aircraft is seen on a situation display and positively identified.
84
IFR Flight
A flight conducted in accordance with the instrument flight rules.
85
Initial Approach Segment
The part of an instrument approach procedure between the initial approach fix and the intermediate approach fix or, where applicable, the final approach fix or point.
86
Instrument Approach Procedure
A series of predetermined manoeuvres by reference to flight instruments with specified protection from obstacles from the initial approach fix, or where applicable, from the beginning of a defined arrival route to a point from which a landing can be completed and thereafter, if a landing is not completed, to a position at which holding or en route obstacle clearance criteria apply.
- NPA (Non Precision Approach) procedure means an instrument approach procedure which utilises lateral guidance but does not utilise vertical guidance.
- (APV) Approach Procedure with Vertical guidance means an instrument procedure which utilises lateral and vertical guidance but does not meet the requirements established for precision approach and landing operations.
- PA (Precision Approach) procedure means an instrument approach procedure using precision lateral and vertical guidance with minima as determined by the category of the operation.
87
Instrument Meteorological Conditions
Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling, less than the minima specified for Visual Meteorological Conditions.
88
Intermediate Approach
That part of an instrument approach procedure between the intermediate approach fix and the final approach fix or point, or between the end of a reversal, racetrack or dead reckoning track procedure and the final approach fix or point, as appropriate.
89
Intermediate Holding Position
A designated position intended for traffic control at which taxiing aircraft and vehicles shall stop and hold until further cleared to proceed, when so instructed by the aerodrome control tower.
90
Known Traffic
Traffic, the current flight details and intentions of which are known to the controller concerned through direct communication or co-ordination.
91
Level
A generic term relating to the vertical position of an aircraft in flight and meaning variously height, altitude or flight level.
92
Manoeuvring Area
That part of an aerodrome to be used for the take-off, landing and taxiing of aircraft, excluding aprons.
93
Minimum Descent Height
In relation to the operation of an aircraft at an aerodrome means the height in a non-precision approach below which descent may not be made without the required visual reference.
94
Minimum Fuel
The term used to describe a situation in which an aircrafts fuel supply has reached a state where little or no delay can be accepted.
95
Minimum Sector Altitude
The lowest safe altitude for instrument flight within sectors of an aid, facility or aerodrome which is published in the appropriate approach chart.
96
Missed Approach Point
The point in an instrument approach procedure at or before which the prescribed missed approach procedure must be initiated in order to ensure that the minimum obstacle clearance is not infringed.
97
Missed Approach Procedure
The procedure to be followed if the approach cannot be continued.
98
Movement Area
That part of an aerodrome to be used for the take-off, landing and taxiing of aircraft, consisting of the manoeuvring area and the apron(s).
99
Night
The time between half an hour after sunset and half an hour before sunrise (inclusive), sunset and sunrise being determined at surface level.
100
Non-Deviating Status
A flight category which entails priority handling for certain flights within specified classes of controlled airspace by prior arrangement with controlling authorities.
101
Non-Precision Approach
An instrument approach using non-visual AIDS for guidance in azimuth or elevation but which is not a precision approach.
102
Obstacle Clearance Height
The lowest height above the elevation of the relevant runway threshold or above the aerodrome elevation as applicable used in establishing compliance with the appropriate obstacle clearance criteria.
103
Omnidirectional Departure
A procedure designed on the basis that an aircraft maintains runway direction until it reaches such a height that it can make a turn in any direction and maintain the prescribed obstacle clearance.
104
Operational Air Traffic
Flights conducted under the control of authority of the military ATS organisation.
105
Position Indication
The visual indication, in non-symbolic and/or symbolic form, on a situation display, of the position of an aircraft, aerodrome vehicle or other object.
106
Position Symbol
The visual indication in symbolic form, on a situation display, of the position of an aircraft, aerodrome vehicle or other object obtained after automatic processing of positional data derived from any source.
107
Precision Approach
An instrument approach using an ILS, MLS or Precision Approach Radar for guidance in both azimuth and elevation.
108
Precision Approach Radar
Primary radar equipment used to determine the position of an aircraft during final approach, in terms of lateral and vertical deviations relative to a nominal approach path, and in range relative to touchdown.
109
Prevailing Visibility
The visibility value that is reached or exceeded within at least half the horizon circle or within at least half of the surface of the aerodrome. These areas could compromise contiguous or non-contiguous sectors.
110
Primary Surveillance Radar
A surveillance radar system which uses reflected radio signals.
111
Procedural Control
Term used to indicate that information derived from an ATS surveillance system is not required for the provision of an ATC service.
112
Procedural Separation
The separation used when providing procedural control.
113
Procedure Turn
A manoeuvre in which a turn is made away from a designated track followed by a turn in the opposite direction to permit the aircraft to intercept and proceed along the reciprocal of the designated track.
114
PSR Blip
The visual indication, in non-symbolic form, on a situation display of the position of an aircraft obtained by primary radar.
115
Advisory Airspace
An airspace of defined dimensions, or designated route, within which Air Traffic Advisory Service is available (EU 923/2012)
116
Racetrack Procedure
A procedure designed to enable the aircraft to reduce altitude during the initial approach segment and/or establish the aircraft inbound when the entry into a reversal procedure is not practical.
117
Radar Approach
An approach, in which the final approach phase is executed, under the direction of a controller using radar.
118
Radar Clutter
The visual indication on a situation display of unwanted signals.
119
Radar Contact
The situation which exists when the radar position of a particular aircraft is seen and identified on a situation display.
120
Radar Control
Term used to indicate that radar-derived information is employed directly in the provision of air traffic control service.
121
Radar Handover
Transfer of responsibility for the control of an aircraft between two controllers using radar, following identification of the aircraft by both controllers.
122
Radar Separation
The separation used when aircraft position information is derived from radar sources.
123
Radar Service
Term used to indicate a service provided directly by means of radar.
124
Radial
A magnetic bearing extending form a VOR/VORTAC/TACAN.
125
Radio Mandatory Zone
Airspace of defined dimensions wherein the carriage and operation of suitable/appropriate radio equipment is mandatory.
126
Radiotelephony
A form of radio communication primarily intended for the exchange of information in the form of speech.
127
Reduced Vertical Separation
Minimum airspace between FL290 and FL410 inclusive designated by the relevant competent authority as being airspace within which a vertical separation minimum of 1000 feet or 300 metres shall be applied.
128
Release Point
The position, time or level at which an arriving aircraft comes under the jurisdiction of an approach control unit.
129
Reporting Point
A specified geographical location in relation to which the position of an aircraft can be reported.
130
Reversal Procedure
A procedure designed to enable an aircraft to reverse direction during the initial approach segment of an instrument approach procedure. The sequence may include procedure turns or base turns.
131
Runway
A defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft.
132
Runway Holding Position
A designated position intended to protect a runway, an obstacle limitation surface, or an ILS/MLS critical/sensitive area at which taxiing aircraft and vehicles shall stop and hold, unless otherwise authorised by the aerodrome control tower.
133
Runway Incursion
Any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of surface designated for the landing and taking off of aircraft.
134
Runway Visual Range
The range over which the pilot of an aircraft on the centre line of a runway can see the runway surface markings or the lights delineating the runway or identifying its centreline.
135
SAFETYCOM
A common frequency (135.475MHz) made available for use at aerodromes where no other frequency is allocated, to enable pilots to broadcast their intentions to other aircraft that may be operating on, or in the vicinity of, the aerodrome.
136
Secondary Surveillance Radar
A surveillance radar system which uses transmitters/receivers (interrogators) and transponders.
137
Semi-circular Cruising Level
Specified cruising levels determined in relation to magnetic track within hemispheres of the compass.
138
SIGMET Information
Information issued by a meteorological watch office concerning the occurrence or expected occurrence of specified en route weather phenomena which may affect the safety of aircraft operations.
139
Significant Point
A specified geographical location used in defining an ATS route or the flight path of an aircraft and for other navigation and ATS purposes.
140
Silent Handover
A transfer of control without a radar handover, made in accordance with local conditions.
141
Situation Display
An electronic display depicting the position and movement of aircraft and other information as required.
142
Special VFR Flight
A VFR flight cleared by air traffic control to operate within a control zone in meteorological conditions below VMC
143
SSR Response
The visual indication in non-symbolic form, on a situation display, of a response from an SSR transponder in reply to an interrogation.
144
Standard Instrument Arrival
A designated IFR arrival route linking a significant point, normally on an ATS route, with a point from which a published instrument approach procedure can be commenced.
145
Standard Instrument Departure
A designated IFR departure route linking rah aerodrome or specified runway of an aerodrome with a specified significant point, normally on a designated ATS route, at which the en route phase of a flight commences.
146
Stepdown Fix
A defined point on the instrument approach track indicating that a critical obstacle has been safely overflown and descent to the next specified level may commence.
147
Stopway
A defined rectangular area at the end of the take-off run available, prepared and designated as a suitable area in which an aircraft can be stopped in the case of a discontinued take-off.
148
Strayed Aircraft
An aircraft which has deviated significantly from its intended track or which reports that it is lost.
149
Surface Visibility
The horizontal visibility as measured at a height of 2 metres above the ground.
150
Surveillance Minimum Altitude Area
Defined area in the vicinity of an aerodrome, depicted on a Surveillance Minimum Altitude Chart, in which the minimum safe levels allocated by a controller vectoring IFR flights with Primary and/or Secondary Radar equipment have been predetermined.
151
Surveillance Radar
Radar equipment used to determine the position of an aircraft in range and azimuth.
152
Taxiing
Movement of an aircraft on the surface of an aerodrome or an operating site under its own power, excluding take-off or landing.
153
Taxiway
A defined path on a land aerodrome established for the taxiing of aircraft and intended to provide a link between one part of an aerodrome and another.
154
Taxiway Holding Position
A designated position at which taxiing aircraft and vehicles may be required to hold in order to provide adequate clearance from a taxiway.
155
Terminal Control Area
A control area normally established at the confluence of ATS routes in the vicinity of one or more major aerodromes.
156
Threshold
The beginning of that portion of the runway useable for landing.
157
Touchdown
The point of intersection of the glide path with the runway.
158
Track
The projection on the earths surface of the path of an aircraft, the direction of which path at any point is usually expressed in degrees from North (true, magnetic or grid).
159
Traffic Avoidance Advance
Advice provided by an air traffic control unit specifying manoeuvres to assist a pilot to avoid collision.
160
Traffic Information
Information issued by an air traffic services unit controller to alert a pilot or controller to other known or observed air traffic which may be in proximity to the position or intended route of flight and to help the pilot.
161
Transfer of Control Point
A defined point located along the flight path of an aircraft, at which the responsibility for providing air traffic control service to the aircraft is transferred from one control unit or control position to the next.
162
Transition Altitude
The altitude at or below which the vertical position of an aircraft is controlled by reference to altitudes. (Note: when QFE is used the vertical position will be with reference to height).
163
Transition Level
The lowest flight level available for use above the transition altitude.
164
Transponder
A receiver/transmitter which will generate a reply signal upon interrogation.
165
Transponder Mandatory Zone
Airspace of defined dimensions within which aircraft are required to operate a transponder in accordance with promulgated procedures.
166
Unidentified Aircraft
An aircraft which has been observed or reported to be operating in a given area but whose identity has not been established.
167
Unknown Traffic
Traffic, the flight details and intentions of which are not known to the controller/FISO.
168
Vectoring
Provision of navigational guidance to aircraft in the form of specific heading, based on the use of an ATS surveillance system.
169
VFR Flight
A flight conducted in accordance with the the visual flight rules.
170
Visibility
Visibility for aeronautical purposes is the greater of:
- the greatest distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognised when observed against a bright background.
- the greatest distance at which lights in the vicinity of 1000 candelas can be seen and identified against an unlit background.
171
Visual Approach
An approach by an IFR flight when part or all of an instrument approach procedure is not completed and the approach is executed with visual reference to terrain.
172
Visual Meteorological Conditions
Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling, equal to or better than specified minima.
173
With the Surface in Sight
Means with the the flight crew being able to see sufficient surface features or surface illumination to enable the flight crew to maintain the aircraft in a desired attitude without reference to any flight instrument and 'when the surface is not in sight' shall be construed accordingly.
174
QFE
Atmospheric pressure corrected to a specific elevation (eg official aerodrome elevation, runway threshold elevation).
175
QNH
Atmospheric pressure corrected to mean sea level, assuming International Standard Atmosphere conditions across the height difference.
176
Regional Pressure Settings
The lowest forecast QNH value for an Altimeter Setting Region, in whole hPa.
(Used for terrain clearance and to establish minimum Flight Levels).
177
Proximity
Aircraft shall not be operated in such proximity to other aircraft as to create a collision hazard.
178
Congested Area
In relation to a city, town or settlement, means any area which is substantially used for residential, industrial, commercial or recreational purposes.
179
QNE
The reading, in feet, on an altimeter with the sub scale set to 1013.25 hPa when the aircraft is at an aerodrome or touchdown elevation.
