If you live very close to the airport you may hear noise from aircraft on the ground. Unlike the noise limits that apply to departing aircraft, there are no limits on other sources of noise that originate from the airport. However, as it is important that a balance is struck between the interests of the local community and the needs of airport users, various controls have been adopted by Heathrow. This page explains the causes of ground noise and what we do about it.
What are the causes?
There are several causes of aircraft noise on the ground at airports. The main factors are:
- Aircraft using reverse thrust to increase their braking after they land
- Aircraft travelling between the runway and stands (where they park)
- Aircraft sitting on their stands with their power units running
- Engine testing
Reverse thrust
Reverse thrust is a way of slowing down aircraft once they have landed. Sometimes, for example, on a wet runway, reverse thrust must be used for safety reasons. However, to reduce disturbance in areas close to Heathrow, pilots are asked not to use reverse thrust after landing between 23:00 and 06:00 hours local, unless they need to for safety reasons. As reverse thrust may be used as part of an aircraft's landing, noise created by it is technically referred to as air noise (as opposed to ground noise) and is included in the annual air noise contours.
Taxiing to and from stands
Aircraft need to taxi to and from the runway and at a large airfield like Heathrow, this may be a fair distance. Although aircraft will taxi with the minimum power possible (it is good for noise and also saves them fuel and emissions), it can still cause disturbance close to the airport. It is for this reason that we work with Air Traffic Control to cut down the amount of time that aircraft are waiting to take off, or are taxiing on the ground, so that their engines are not running for so long.
We also work with the people responsible for allocating stands to arriving aircraft so that the distance aircraft have to taxi is reduced, enabling them to park and shut down their engines sooner.
Running power units on the ground
Auxiliary Power Units (APUs) are small engines and generators in the tail of an aircraft that are used to deliver electrical power and cabin conditioning while on the ground. In order to reduce noise, we specify conditions for APU usage in airport procedures to limit their use and supply alternative systems for them to use whilst on the ground including Fixed Electrical Ground Power (FEGP) and Pre Conditioned Air (PCA). This is essentially plugging aircraft into the mains electrical supply while they are parked. This directly leads to a reduction in ground noise.
Engine testing
To ensure that an aircraft is working safely, it is sometimes necessary to run one or more engines while the aircraft is on the ground. These engine tests can either be low power runs or high power runs. Both types are limited to how long the engines can run for to complete the check.
Low power runs can take place while an aircraft is parked on a stand by the terminals. There are some restrictions on what time these can occur, depending on the location of the stand, to limit noise to the community. High power runs must take place at one of a limited number of safe designated areas on the airfield, or in a dedicated acoustic pen located to the east of the airfield. During the night, high power runs must take place in an acoustic pen. All testing requires permission from the airport authority prior to the engine run taking place.
