Skip to Content
Saved Flights
Your Saved Flights

No Saved Flights

  • Glossary

    At-a-glance guide to help you understand the terms used in articles and discussions about aircraft noise.


    Arrivals Code of Practice.


    Aeronautical Information Publication.

    Airbus A320

    Small two-engine aircraft, predominantly used for short-haul domestic and European flights. Typically carries 120-130 passengers.

    Airbus A380

    Large four-engine aircraft, used for long-haul and intercontinental travel. The largest passenger aircraft in service, known as a ‘superjumbo’. Typically carries more than 500 passengers.

    Airports Commission

    Set up by the Government in 2012 to determine the future of airport capacity in the South East of England. The Commission was tasked with discovering if capacity is needed, and if it is needed, where that capacity should go. The Commission was made up of seven members, chaired by Sir Howard Davies.


    Attitudes to Noise from Aviation Sources in England.


    Aircraft Noise Monitoring Advisory Committee. The committee is chaired by the Department for Transport and comprises, among others, representatives of the airlines, Heathrow, Gatwick and Stansted airports and airport consultative committees.


    Auxiliary power unit. A power unit located on the aircraft.


    Air traffic control.


    British Airports Authority.

    Balanced approach

    An approach to airport noise agreed by governments globally that takes into account the needs and requirements of residents as well as the interests of the aviation industry.

    Boeing 747

    Large four-engine aircraft, used for long-haul and intercontinental travel, nicknamed the ‘jumbo jet’. Typically carries between 300-400 passengers.

    Boeing 777

    Large two-engine aircraft, used for long-haul and intercontinental travel. Typically carries 300-400 passengers.

    Boeing 787

    The Boeing 787 Dreamliner is the newest aircraft operating at Heathrow. Medium-sized two-engine aircraft, which is 60% quieter than the aircraft that it replaces. A very long-range aircraft, it carries around 250 passengers.


    Civil Aviation Authority.


    Continuous descent approach.

    Cranford Agreement

    A verbal agreement made in the 1950s to avoid use of the northern runway for take-offs in an easterly direction over the village of Cranford.


    A unit of sound pressure level, adjusted in accordance with the A-weighting scale, which takes into account the increased sensitivity of the human ear at some frequencies.

    Decibel (dB)

    The decibel is a logarithmic unit of measurement that expresses the magnitude of a physical quantity relative to a specified or implied reference level. Its logarithmic nature allows very large or very small ratios to be represented by a convenient number. Being a ratio, it is a dimensionless unit. Decibels are used for a wide variety of measurements including acoustics, and for audible sound A-weighted decibels (dBA) are commonly used.


    Department for Environment, Food and Rural Affairs (UK government).


    The Department for Transport is the UK government department responsible for civil aviation including night quotas and environmental standards. The DfT has direct control of noise at Heathrow.


    Prevailing winds blowing from the east.

    Easterly operations

    When easterly operations are in effect, planes approach Heathrow over Windsor to the west, and take off towards London. Heathrow switches to easterly operations when the wind is blowing from the east – which it does about 30% of the time.


    European Civil Aviation Conference.

    Engine bypass ratio

    The ratio of the amount of air that passes around the outside of the combustion chambers of an aircraft gas turbine to that passing through them.


    Environmental Research and Consultancy Department of the Civil Aviation Authority.


    Fixed electrical ground power.


    Flight Evaluation Unit.


    Flight Operations Performance Committee.

    Fly Quiet and Green programme

    The Fly Quiet and Green programme aims to further encourage airlines to use quieter aircraft and to fly them in the quietest possible way. The programme includes the UK's first ever league table that ranks airlines according to their noise performance.


    Ground power unit.


    Heathrow Association for the Control of Aircraft Noise. A campaigning organisation that represents people living under Heathrow flight paths, highlighting concerns about issues such as noise and pollution.

    Heathrow Community Engagement Board

    The Heathrow Community Engagement Board (HCEB) acts as a focal point for engagement between Heathrow airport, local authorities, community groups, passengers and other airport users. The creation of a community engagement board was one of the measures recommended by the Airports Commission to help ensure that all local communities can contribute effectively to the planning process for the proposed expansion of the airport.

    Heathrow Communities Fund

    Each year Heathrow donates £750,000 to local community projects through the Heathrow Communities Fund. The fund makes grants to local charitable initiatives that support young people, help protect the environment or encourage sustainable development and eco-education, as well as smaller community-focused projects.

    Heathrow Community Noise Forum

    The Heathrow Community Noise Forum (HCNF) was set up in 2015 and is made up of representatives from local authorities around Heathrow, NATS, BA, DfT, CAA and Heathrow. Heathrow set up the forum in response to local concerns regarding future changes to airspace as a result of the Government’s airspace modernisation strategy.

    Hub airport

    A hub airport is an airport where local passengers combine with transfer passengers to allow airlines to operate flights to destinations that could not be supported by local demand alone.


    The International Air Transport Association is a trade association representing 240 of the world’s airlines or 84% of total air traffic. IATA supports many areas of aviation activity and help formulate industry policy on critical aviation issues.


    International Civil Aviation Organization.


    The Instrument Landing System (ILS) is a precision runway approach aid employing two radio beams to provide pilots with vertical and horizontal guidance during the final approach to landing.

    Landing interval

    The amount of separation between aircraft on approach.


    The A-weighted average sound level over the 12 hour day period of 07:00 – 19:00.


    The day, evening, night level. Lden is a logarithmic composite of the Lday, Levening, and Lnight levels but with 5 dB(A) being added to the Levening value and 10 dB(A) being added to the Lnight value.


    Equivalent sound level of aircraft noise in dBA, often called equivalent continuous sound level. For conventional historical contours this is based on the daily average movements that take place in the 16 hour period (07:00 – 23:00 LT) during the 92-day period 16 June to 15 September inclusive.


    The A-weighted average sound level over the four-hour evening period of 19:00 – 23:00.


    The A-weighted average sound level over the eight-hour night period of 23:00 – 07:00.


    Formerly known as National Air Traffic Services Ltd, NATS is licensed to provide en-route air traffic control for the UK and the Eastern part of the North Atlantic, and also provides air traffic control services at several major UK airports including Heathrow, Gatwick and Stansted.

    Noise Action Plan

    We are required by EU law to produce a five-year plan setting out proposals for how we will tackle noise.

    Noise exposure contour

    A noise contour is a line on a map that represents equal levels of noise exposure. Aircraft noise maps, which show lines joining points of equal noise, are a powerful tool for illustrating the impact of aircraft noise around airports. The Environmental Research and Consultancy Department (ERCD) of the Civil Aviation Authority developed the UK civil aircraft noise contour model, ANCON, which calculates the contours from data describing aircraft movements, routes, noise generation and sound propagation. The number of annual flights, aircraft types and flight tracks are critical inputs to the contour model.

    Noise mitigation

    A set of strategies to reduce noise pollution or to reduce the impact of noise.


    Noise preferential route.


    Noise and Track Keeping monitoring system. The NTK system associates radar data from air traffic control with related data from both fixed (permanent) and mobile noise monitors at prescribed positions on the ground.

    Performance Based Navigation (PBN)

    A broad range of technologies that are moving aviation away from a ground-based navigation towards relying more on the performance and capabilities of equipment on board the aircraft.


    Perceived noise level is measured in PNdB. Its measurement involves analyses of the frequency spectra of noise events as well as the maximum level.


    Planning Policy Guidance.


    Quota Count – the basis of the London airports night restrictions regime.

    Runway alternation

    At Heathrow during periods of westerly operations, one runway is used by landing aircraft between 6am and 3pm and the other for departures. Arrivals and departures then switch to the other runway from 3pm to the last departure. The pattern alternates on a weekly basis. For example, one week flights will land on the southern runway in the morning and the northern runway in the afternoon. The following week, flights will land on the northern runway in the morning and the southern runway in the afternoon. There is also a runway alternation pattern for flights during the night.


    Sound exposure level. The level generated by a single aircraft at the monitoring point. This is normalised to a one-second burst of sound and takes account of the duration of the sound as well as its intensity.


    Standard Instrument Departure route.


    Start-of-roll: The position on a runway where aircraft commence their take-off runs.


    Secretary of State.

    Summer Leq

    Equivalent sound level of aircraft noise in dB(A), often called equivalent continuous sound level. For conventional historical contours this is based on the daily average movements that take place in the 16-hour period (from 7am to 11pm local time) during the 92 day period from 16 June to 15 September inclusive.

    Sustainable Aviation

    A UK aviation industry initiative aiming to set out a long-term strategy for the industry to address sustainability issues.


    Route used by aircraft moving to and from the runway to their allocated parking stand.


    Tactically Enhanced Arrivals Mode refers to using both runways simultaneously for arrivals to clear major backlogs of flights waiting to land.


    Heathrow Airport Terminal 5.

    Variable landing charges

    Heathrow’s landing charges are varied according to how noisy aircraft are. This is to encourage airlines to use their quietest aircraft. For example, the noisiest type of aircraft operating at Heathrow pays ten time more than the quietest aircraft.

    Vortex strike

    A vortex is a circulating current of air generated by planes. It can sometimes strike and damage the roofs of houses located under a flight path. Pitched roofs with loose-laid tiles are prone to vortex damage.


    A map-based tool that allows people to track specific flights on specific days in relation to where they live.

    Webtrak My Neighbourhood

    A map-based tool that gives a general overview of where planes fly and how the distribution of flights changes over time.


    Prevailing winds blowing from the west.

    Westerly operations

    Around Heathrow the wind usually blows from the west. Because aircraft must land into the wind, the majority of aircraft arrive from the east (over London) and take off towards the west (over Berkshire/Surrey). This is known as westerly operations.

    Westerly preference

    Aircraft usually land and take-off into the wind. A westerly preference is operated at Heathrow, which means that during periods of light easterly winds (up to 5 knots), aircraft will often continue to land in a westerly direction making their final approach over London. The westerly preference was introduced in the 1960s to reduce numbers of aircraft taking off in an easterly direction over London, i.e. over the most heavily populated side of the airport.


    A map-based tool that allows people to find out which aircraft flew over them, when and how often.