Glossary

A

ADS-B – Automatic Dependent Surveillance-Broadcast
ADS-B uses ground-based antennas and in-aircraft dis­plays to alert pilots to the position of other aircraft relative to their flight path. ADS-B is a key element of NextGen.

AGL – Above Ground Level
Height measured with respect to the ground.

Air Carrier
A commercial airline with published schedules operating at least five round trips per week.

Air Taxi
An aircraft certificated for commercial service available for hire on demand.

ALP – Airport Layout Plan
The official, FAA approved map of an airport’s facilities.

ALS – Approach Lighting System
Radiating light beams guiding pilots to the extended centerline of the runway on final approach and landing.

Ambient Noise Level
The existing background noise level characteristic of an environment.

Approach Lights
High-intensity lights located along the approach path at the end of an instrument runway. Approach lights aid the pilot as he transitions from instrument flight con­ditions to visual conditions at the end of an instrument ap­proach.

APU – Auxiliary Power Unit
A self-contained generator in an aircraft that produces power for ground operations of the electrical and ventilation systems and for starting the en­gines.

Arrival
The act of landing at an airport.

Arrival Procedure
A series of directions on a published approach plate or from air traffic control personnel, using fix­es and procedures, to guide an aircraft from the en-route en­vironment to an airport for landing.

Arrival Stream
A flow of aircraft that are following similar arrival procedures.

ARTCC – Air Route Traffic Control Center
A facility providing air traffic control to aircraft on an IFR flight plan within controlled airspace and principally during the en-route phase of flight. Also referred​ to as Center.

ATC – Air Traffic Control
The control of aircraft traffic, in the vicinity of airports from control towers, and in the airways between airports from control centers.

ATCT – Air Traffic Control Tower
A central operations tower in the terminal air traffic control system with an associ­ated IFR room if radar-equipped, using air/ground communi­cations and/or radar, visual signaling and other devices to provide safe, expeditious movement of air traffic.

Avionics
Airborne navigation, communications, and data display equipment required for operation under specific air traffic control procedures.

Altitude MSL
Aircraft altitude measured in feet above mean sea level (MSL).

 

B

Backblast
Low frequency noise and high velocity air gener­ated by jet engines on takeoff.

Base Leg
A flight path at right angles to the landing run­way. The base leg normally extends from the downwind leg to the intersection of the extended runway centerline.

 

C

CDA – Continuous Descent Approach
An efficient, reduced power method by which aircraft approach airports for land­ing. It is designed to reduce level off segments during de­scent, reducing fuel consumption and noise. Also known as Optimized Profile Descent (ODP).

Center
A facility providing air traffic control to aircraft on an IFR flight plan within controlled airspace and principally during the en-route​ phase of flight. Also known as Air Route Traffic Control Center (ARTCC).

Cloud Ceiling
The height above the earth’s surface of the lowest layer of clouds that is reported as “broken” or “overcast.” Is reported in feet AGL.

CNEL – Community Noise Equivalent Level
A noise metric required by the California Airport Noise Standards for use by airport proprietors to measure aircraft noise levels. CNEL includes an additional weighting for each event occurring during the evening (7:00pm – 9:59pm) and nighttime (10:00pm – 6:59am) periods to account for increased sensi­tivity to noise during these periods. Evening events are treated as though there were three and nighttime events are treated as though there were ten. This results in a 4.77 and 10 decibel penalty for operations occurring in the evening and nighttime periods, respectively.

CNEL Contour
The “map” of noise exposure around an airport as expressed using the CNEL metric. A CNEL con­tour is computed using the FAA-approved Integrated Noise Model (INM), which calculates the aircraft noise exposure near an airport.

Commuter Airline
Operator of small aircraft (maximum size of 30 seats) performing scheduled (maximum size of 30 seats) performing service between two or more points.

 

D

Decibel (dB)
In sound, decibels measure a scale from the threshold of human hearing, 0 dB, upward towards the threshold of pain, about 120-140 dB. Because decibels are such a small measure, they are computed logarithmically and cannot be added arithmetically. An increase of ten dB is perceived by human ears as a doubling of noise.
Delay Vectors – When ATC assigns an aircraft a heading that takes it off course, before bringing it back on course. Delay vectors may be used for many reasons such as for aircraft traffic or to create spacing between aircraft.

dBA
A-weighted decibels adjust sound pressure towards the frequency range of human hearing.

dBC
C-weighted decibels adjust sound pressure towards the low frequency end of the spectrum. Although less con­sistent with human hearing than A- weighting, dBC can be used to consider the impacts of certain low frequency oper­ations.

Decision Height
The height at which a decision must be made during an instrument approach either to continue the approach or to execute a missed approach.

Departure
The act of an aircraft taking off from an airport.

Departure Procedure
A published IFR departure proce­dure describing specific criteria for climb, routing, and com­munications for a specific runway at an airport.

Displaced Threshold
A threshold that is located at a point on the runway other than the physical beginning. Aircraft can begin departure roll before the threshold, but cannot land before it.

DME – Distance Measuring Equipment
Equipment (airborne and ground) used to measure, in nautical miles, a slant range distance of an aircraft from the DME navigation­al aid.

DNL – Day/Night Average Sound Level
The daily aver­ age noise metric in which that noise occurring between 10:00 p.m. and 7:00 a.m. is penalized by 10 dB. DNL isoften expressed as the annual-average noise level.

DNL Contour
The “map” of noise exposure around an airport as expressed using the DNL metric. A DNL con­tour is computed using the FAA-approved Integrated Noise Model (INM), which calculates the aircraft noise exposure near an airport.

Downwind Leg
A flight path parallel to the landing runway in the direction opposite the landing direction.

Duration
The length of time in seconds that a noise event lasts. Duration is usually measured in time above a specific noise threshold.

 

E

En route
The portion of a flight between departure and arrival terminal areas.

Exceedance
Whenever an aircraft overflight produces a noise level higher than the maximum decibel value estab­lished for a particular monitoring site, the noise threshold is surpassed and a noise exceedance occurs. An exceed- ance may take place during approach, takeoff, or possibly during departure ground roll before lifting off.

 

F

FAA
The Federal Aviation Administration is the agency responsible for aircraft safety, movement and controls. FAA also administers grants for noise mitigation projects and approves certain aviation studies including FAR Part 150 studies, Environmental Assessments, Environmental studies, Environmental Assessments, Environ Impact Statements, and Airport Layout Plans.

FAR – Federal Aviation Regulations
The rules and regulations, which govern the operation of aircraft, airways, and airmen.

FAR Part 36
A Federal Aviation Regulation defining maximum noise emissions for aircraft.

FAR Part 91
A Federal Aviation Regulation governing the phase out of Stage 1 and 2 aircraft as defined under FAR Part 36.

FAR Part 150
A Federal Aviation Regulation governing noise and land use compatibility studies and programs.

FAR Part 161
A Federal Aviation Regulation governing aircraft noise and access restrictions.

Final Approach
The last leg in an aircraft’s approach to landing, when the aircraft is lined up with the runway and is descending for landing.

Fix
A geographical position determined by visual references to the surface, by reference to one or more Navaids, or by other navigational methods.

Fleet Mix
The mix or differing aircraft types operated at a particular airport or by an airline.

Flight Plan
Specific information related to the intended flight of an aircraft. A flight plan is filed with a Flight Service Station or Air Traffic Control facility.

FMS – Flight Management System
A specialized computer system in an aircraft that automates a number of in-flight tasks, which reduces flight crew workload and im­proves the precision of the procedures being flown.

 

G

GA – General Aviation
Civil aviation excluding air carri­ers, commercial operators and military aircraft.

GAP Departure
An aircraft departure via Runways 28 at San Francisco International Airport to the west over San Bruno, South San Francisco, Daly City, and Pacifica.

Glide Slope
Generally a 3-degree angle of approach to a runway established by means of airborne instruments dur­ing instrument approaches, or visual ground aids for the visual portion of an instrument approach and landing.

Go-Around
An aborted landing of an aircraft that is on final approach.

GPS – Global Positioning System
A satellite based radio positioning, navigation, and time-transfer system.

GPU – Ground Power Unit
A source of power, generally from the terminals, for aircraft to use while their engines are off to power the electrical and ventilation systems on the aircraft.

Ground Effect
The excess attenuation attributed to ab­sorption or reflection of noise by manmade or natural fea­tures on the ground surface.

Ground Track
Is the path an aircraft would follow on the ground if its airborne flight path were plotted on the ground the terrain.

 

H

High Speed Exit Taxiway
A taxiway designed and provided with lighting or marking to define the path of air­craft traveling at high speed from the runway center to a point on the center of the taxiway.

 

I

IDP – Instrument Departure Procedure
An aeronautical chart designed to expedite clearance delivery and to facili­tate transition between takeoff and en route operations. IDPs were formerly known as SIDs or Standard Instrument Departure Procedures.

IFP Gateway
Notification method to solicit comments from industry partners and air traffic

IFR – Instrument Flight Rules
Rules and regulations es­tablished by the FAA to govern flight under conditions in which flight by visual reference is not safe.

ILS – Instrument Landing System
A precision instrument approach system which normally consists of a localizer, glide slope, outer marker, middle marker, and approach lights.

IMC – Instrument Meteorological Conditions
Weather conditions expressed in terms of visibility, distance from clouds, and cloud ceilings during which all aircraft are re­quired to operate using instrument flight rules.

Instrument Approach
A series of predetermined maneuvers for the orderly transfer of an aircraft under in­strument flight conditions from the beginning of the initial approach to a landing, or to a point from which a landing may be made visually.

 

K

Knots
A measure of speed used in aerial navigation. One knot is equal to one nautical mile per hour (100 knots = 115 miles per hour).

 

L

Load Factor
The percentage of seats occupied in an aircraft.

Lmax
The peak noise level reached by a single aircraft event.

Localizer
A navigational aid that consists of a directional pattern of radio waves modulated by two signals which, when receding with equal intensity, are displayed by com­patible airborne equipment as an “on-course” indication, and when received in unequal intensity are displayed as an “off-course” indication.

LDA – Localizer Type Directional Aid
A facility of com­parable utility and accuracy to a localizer, but not part of a complete ILS and not aligned with the runway.

 

M

Middle Marker
A beacon that defines a point along the glide slope of an ILS, normally located at or near the point of decision height.

Missed Approach Procedure
A procedure used to redi­rect a landing aircraft back around to attempt another land­ing. This may be due to visual contact not established at authorized minimums or instructions from air traffic control, or for other reasons.

 

N

NAS – National Airspace System
The common net­work of U.S. airspace; air navigation facilities, equipment and services, airports or landing areas; aeronautical charts, information and services; rules, regulations and procedures, technical information, manpower and material.

Nautical Mile
A measure of distance used in air and sea navigation. One nautical mile is equal to the length of one minute of latitude along the earth’s equator. The nauti­cal mile was officially set as 6076.115 feet. (100 nautical miles = 115 statute miles)

Navaid
Navigational Aid.

NCT – Northern California TRACON
The air traffic con­trol facility that guides aircraft into and out of San Francisco Bay Area airspace.

NDB – Non-Directional Beacon
Signal that can be read by pilots of aircraft with direction finding equipment. Used to determine bearing and can “home” in or track to or from the desired point.

NEM – Noise Exposure Map
A FAR Part 150 require­ment prepared by airports to depict noise contours. NEMs also take into account potential land use changes around airports.

NextGen
The Next Generation of the national air trans­portation system. NextGen represents the movement from ground-based navigation aids to satellite-based navigation.

NMS – See RMS

Noise Contour – See CNEL and DNL Contour.

Non-Precision Approach Procedure – A standard instru­ment approach procedure in which no electronic glide slope is provided.

 

O

OAPM – Optimization of Airspace and Procedures in the Metroplex
This is a part of the FAA’s Next Generation of air traffic control plans for 21 areas with multiple airports in the United States.

O.set ILS – Offset Parallel Runways
Staggered runways having centerlines that are parallel.

Operation
A take-off, departure or overflight of an aircraft. Every flight requires at least two operations, a take-off and landing.

Outer Marker
An ILS navigation facility in the terminal area navigation system located four to seven miles from the runways edge on the extended centerline indicating the beginning of final approach.

Overflight
Aircraft whose flights originate or terminate outside the metropolitan area that transit the airspace without landing.

OPD – Optimized Profile Descent
An efficient, reduced power method by which aircraft approach airports for land­ing. It is designed to reduce level off segments during de­scent, reducing fuel consumption and noise.

 

P

PASSUR System – Passive Surveillance Receiver
A sys­tem capable of collecting and plotting radar tracks of individual aircraft in flight by passively receiving transponder signals.

PAPI – Precision Approach Path Indicator
An airport lighting facility in the terminal area used under VFR conditions. It is a single row of two to four lights, radiating high intensity red or white beams to indicate whether the pilot is above or below the required runway approach path.

PBN – Performance Based Navigation
Area navigation based on performance requirements for aircraft operating along an IFR route, on an instrument approach procedure or in a designated airspace.

Preferential Runways
The most desirable runways from a noise abatement perspective to be assigned whenever safety, weather, and operational efficiency permits.

Precision Approach Procedure
A standard instrument approach procedure in which an electronic glide slope is provided, such as an ILS. GPS precision approaches may be provided in the future.

PRM – Precision Runway Monitoring
A system of high-resolution monitors for air traffic controllers to use in landing aircraft on parallel runways separated by less than 4,300’.

 

R

Navigational guidance where air traffic controller issues a compass heading to a pilot.

An airport for general aviation and other aircraft that would otherwise use a larger and busier air car­rier airport.

RMS – Remote Monitoring Site
A microphone placed in a community and recorded at San Francisco International Airport’s Noise Monitoring Center. A network of 29 RMS’s generate data used in preparation of the airport’s Noise Exposure Map.

RNAV – Area Navigation
A method of IFR navigation that allows an aircraft to choose any course within a network of navigation beacons, rather than navigating directly to and from the beacons. This can conserve flight distance, reduce congestion, and allow flights into airports without beacons.

RNP – Required Navigation Performance – A type of performance-based navigation (PBN) that allows an air­craft to fly a specific path between two 3- dimensionally de­fined points in space. RNAV and RNP systems are funda­mentally similar. The key difference between them is the requirement for on- board performance monitoring and alerting. A navigation specification that includes a require­ment for on-board navigation performance monitoring and alerting is referred to as an RNP specification. One not hav­ing such a requirement is referred to as an RNAV specifica­tion.

Run-up – A procedure used to test aircraft engines after maintenance to ensure safe operation prior to returning the aircraft to service. The power settings tested range from idle to full power and may vary in duration.
Run-up Locations – Specified areas on the airfield where scheduled run-ups may occur. These locations are sited, so as to produce minimum noise impact in surrounding neigh­borhoods.

Runway – A long strip of land or water used by aircraft to land on or to take off from.

S

Sequencing Process – Procedure in which air traffic is merged into a single flow, and/or in which adequate separa­tion is maintained between aircraft.
Shoreline Departure – Departure via Runways 28 that uti­lizes a right turn toward San Francisco Bay as soon as fea­sible. The Shoreline Departure is considered a noise abate­ment departure procedure.

SID – Standard Instrument Departure – An aeronautical chart designed to expedite clearance delivery and to facili­tate transition between takeoff and enroute operations.

SENEL – Single Event Noise Exposure Level – The noise exposure level of a single aircraft event measured over the time between the initial and final points when the noise level exceeds a predetermined threshold. It is important to distin­guish single event noise levels from cumulative noise levels such as CNEL. Single event noise level numbers are gener­ally higher than CNEL numbers, because CNEL represents an average noise level over a period of time, usually a year.

Single Event – Noise generated by a single aircraft over­flight.

SOIA – Simultaneous Offset Instrument Approach is an approach system permitting simultaneous Instrument Landing System approaches to airports having staggered but parallel runways. SOIA combines Offset ILS and regular ILS definitions.

STAR – Standard Terminal Arrival Route is a published IFR arrival procedure describing specific criteria for descent, routing, and communications for a specific run­way at an airport.

T

Taxiway – A paved strip that connects runways and terminals providing the ability to move aircraft so they will not interfere with takeoffs or landings.

Terminal Airspace – The air space that is controlled by a TRACON.
Terminal Area – A general term used to describe airspace in which approach control service or airport traffic control service is provided.
Threshold – Specified boundary.

TRACON -Terminal Radar Approach Control – is an FAA air traffic control service to aircraft arriving and de­parting or transiting airspace controlled by the facility. TRA-CONs control IFR and participating VFR flights. TRACONs control the airspace from Center down to the ATCT.

V

Vector – A heading issued to a pilot to provide navigational guidance by radar. Vectors are assigned ver­bally by FAA air traffic controllers.

VFR – Visual Flight Rules are rules governing proce­dures for conducting flight under visual meteorological con­ditions, or weather conditions with a ceiling of 1,000 feet above ground level and visibility of three miles or greater. It is the pilot’s responsibility to maintain visual separation, not the air traffic controller’s, under VFR.

Visual Approach – Wherein an aircraft on an IFR flight plan, operating in VFR conditions under the control of an air traffic facility and having an air traffic control authori­zation, may proceed to destination airport under VFR.

VASI – Visual Approach Slope Indicator – An airport lighting facility in the terminal area navigation system used primarily under VFR conditions. It provides vertical visual guidance to aircraft during approach and landing, by radiat­ing a pattern of high intensity red and white focused light beams, which indicate to the pilot that he/she is above, on, or below the glide path.

VMC – Visual Meteorological Conditions – weather conditions equal to or greater than those specified for air­craft operations under Visual Flight Rules (VFR).

VOR – Very High Frequency Omni-directional Range – A ground based electronic navigation aid transmit­ting navigation signals for 360 degrees oriented from mag­netic north. VOR is the historic basis for navigation in the national airspace system.