1. What is noise, exactly?

Noise is a phenomenon that is omnipresent in the modern world. It is defined as sounds that are undesirable or disturbing. Generally speaking, the louder a sound, the more disturbing it is. Sensitivity to noise, however, can vary greatly from one person to another and even from one moment to another: two sounds of the same intensity may be perceived in very different ways. Some people enjoy listening to a very loud rock concert even though the sound level can sometimes exceed the hearing-damage threshold. But somebody who doesn’t like rock music or is engaged in an activity demanding concentration will be disturbed if they are near the same concert. 

2. How is noise perceived and measured?

Sound is vibration or waves transmitted through the air that can be perceived by ears. Sound is actually minuscule variations in air pressure, which are picked up by the tympanic membrane (eardrum).

Sound has frequency and intensity.

  • The frequency or pitch of a sound is measured in Hertz (vibrations per second). The higher the frequency, the higher-pitched the sound; the lower the frequency, the lower-pitched the sound.
  • The intensity or level of sound corresponds to acoustic pressure, which is most commonly measured in decibels (dB). Because the human ear’s interpretation of sound intensity varies with the frequency of a sound, sound-level meters use a so-called A-weighting filter, which gives more emphasis to higher-frequency sounds than lower-frequency ones. So ambient noise is measured in A-weighted decibels, or dB(A).

It is important to remember that the decibel scale is a logarithmic scale: 0 dB corresponds to the limit of audibility and 140 dB, to the pain threshold.

Decibels are not additive. Two lawnmowers each generating 60 decibels don’t make a noise of 120 dB, but of 63 dB; similarly, 10 mowers at 60 dB each will generate a total sound level of 70 dB.

An increase of 3 dB (a multiplication of the noise source by 2) is perceptible by our ears. A 10-dB increase in sound level (multiplication of the noise source by 10) is perceived by our ears as double the noise.

3. How do airplanes generate noise?

There are two main sources of airplane noise: engine noise and aerodynamic noise (caused by the flow of air around an aircraft in flight). When a plane takes off, and is using maximum thrust, engine noise is predominant. When a plane lands, the aerodynamic noise that is produced can be as loud as the engine noise.

4. Are there differences from one type of aircraft to another?

Generally speaking, bigger planes make more noise than smaller ones. But size isn’t everything! Engine technology has improved greatly in recent years, so some older, smaller aircraft can be noisier than the latest-generation wide-body jets.

The acoustic performances of each type of air transport aircraft are characterized by three noise-level measurements determined according to procedures defined by the International Civil Aviation Organization (ICAO). These three noise levels are measured on approach, takeoff under full power, and overflight. The standards also consider the mass of the aircraft and the number of engines.

The aerospace industry currently distinguishes between several generations of aircraft, referred to as "chapters." There can be a difference in sound level of up to 8 dB from one generation to another, which is considerable.

  • Chapter 2 aircraft are older planes dating from before 1977, equipped with earlier-generation engines. Apart from exceptions, these aircraft have not been allowed to fly in Canada since 2002.
  • Chapter 3 aircraft correspond to the majority of commercial planes currently in operation. Note that some Chapter 2 aircraft have been fitted with noise-attenuation devices, called “hush kits,” to improve their acoustic certification. These aircraft are marginally compliant with Chapter 3 standards, so they are louder than aircraft that are certified Chapter 3 when manufactured.
  • Chapter 4 is a new noise-certification standard introduced by ICAO in 2002, which all new aircraft built after 2006 must comply with.

Noise Certification - Major Aircraft Operating at Montréal-Trudeau:

Air carriers choose their fleet of aircraft. Airplanes and helicopters must meet international noise certification standards that are adopted by the ICAO Council (International Civil Aviation Organization). These standards take into account the mass of the aircraft and the number of engines. They also establish the method to be used to evaluate noise levels.

Transport Canada issues certifications for the operation of aircraft in Canada. All aircraft must comply with ICAO noise standards that are incorporated in Canadian Aviation Regulations.

When certifying an aircraft, measurements must be made at three certification points corresponding to the approach, take-off and flyover, as shown below (taken from the Aircraft Noise  section of the ICAO site).

Certification - illustation OACI.jpg

Location of certification points for take-off and landing:

• Fly-over (take-off): point located at 6.5 km from the start of rolling (brake-release point), under the take-off flight path

• Approach: point located at 2 km from the runway threshold, under the approach flight path

The levels thus measured are corrected according to the tone of the recorded sounds and their duration. The sound level thus obtained is expressed in EPNdB or effective perceived noise level.  As a result, certification levels can not be compared with those read by sound level meters, which are usually expressed in dB (A).

Certification noise levels in EBNdB (cannot be compared with dB(A) noise levels)

The following aircraft represent 77 % of the fleet that operated in YUL Montréal-Trudeau in 2019.

2019-FAQ-Q4 - Certification-1-A.jpg

2019-FAQ-Q4 - Certification-2-A.jpg

2019-FAQ-Q4 - Certification-3-A.jpg

5. What types of aircraft operate at Montréal-Trudeau?

Virtually all passenger transport aircraft operating out of Montréal–Trudeau are certified Chapter 3 or Chapter 4. There are still some aircraft there were recertified as Chapter 3 because they are equipped with noise mufflers known as "hush kits". These aircraft represent a very small percentage of the fleet operating in Montréal-Trudeau and are used for service to northern destinations. They provide an essential service to these isolated areas.

6. How many runways are found in Montréal-Trudeau and how are they designated?

There is a universal system for naming airport runways. The number of the runway corresponds to its angle vis-à-vis magnetic north. For example, Runway 28 is at a 280-degree angle, and Runway 10 at 100 degrees, with the difference between the two directions on the same runway always being 180 degrees. Additionally, when two runways are parallel, they are differentiated by the letters R and L, depending on whether they are to the right or left of one another. Montréal–Trudeau has six runways for navigation purposes: 10 and 28, 06R and 24L and 06L and 24R. This configuration has remained unchanged since 1958.


7. What determines the use of runways in Montréal-Trudeau?

The use of runways is dictated first and foremost by flight safety considerations, and particularly by weather conditions. Planes notably have to land and take off against the wind. Operating conditions (runway length, aircraft type, air traffic, etc.) are also very important. The temporary closing of a runway, for example for repair work, can also have the effect of concentrating traffic on the airport’s other runways. Finally, there is  a priority runway system in place for night operations.

The table below shows runway use statistics for 2020. Runway use statistics for 2006 to 2019 are available in the Indicators section. 

Runway use statistics - 2020
Runway NO. OF ARRIVALS % no. of departures %
06L (north) 4,950 10% 1,524 3%
06R (south) 8,988 19% 13,159 28%
10 0 0% 0 0%
24L (south) 20,509 43%


24R (north) 12,818 27% 3,682 8%
28 0 0% 0 0%
Total 47,265 100% 47,520 100%



8. Why are there planes over my neighbourhood?

Planes are likely to fly over most of Montréal’s neighbourhoods at any time during the day. The majority of aircraft flying over Montréal take off from or land at Montréal–Trudeau. There are other airports nearby, however, including the one in St. Hubert. Often, planes flying over Lachine, for example, are departing from or arriving at St. Hubert.

After takeoff, jets may bank left or right, depending on their destination, as soon as they reach an altitude of 3,000 feet; propeller planes, meanwhile, must turn as soon as possible after takeoff to clear the way for jets, which fly faster. Aircraft landing at Montréal–Trudeau must follow a very precise trajectory, directly in line with the runway and on a 3° angle of descent. Since there are six runways (three physical runways that can each be used in two directions), there are six approach corridors, which take aircraft over many neighbourhoods.


9. Why are there more planes at certain times of day?

An airport has morning and evening “rush hours." Air transport is not very different from other modes of transportation. On highways, bridges, as well as subway and commuter trains, there is always more traffic when people are travelling to or from work.

The same goes for air transport: many domestic and transborder flights leave early in the morning, carrying businesspeople who return in the evening of the same day.

On transatlantic routes, meanwhile, planes usually arrive in the afternoon and leave in the evening. To enable two daily turnarounds, some planes serving southern destinations leave very early in the morning, return in the afternoon, take off again, and return late at night.

10. Why do I hear planes on certain days but not on others?

It all depends on the wind direction and runway use.

For safety reasons, airplanes always take off and land into the wind. In Montréal, the prevailing winds are southwesterly, so planes most often take off towards Lac St-Louis, mainly from the south runway (24L), and land on the north (24R) and south (24L) runways.


If the winds are from the northeast, planes take off and land in the opposite direction, on the south (06R) and north (06L) runways.


Various factors, such as work on a runway or taxiway, can lead to changes in the normal operating mode.

11. Are takeoffs noisier than landings?

Generally speaking, an aircraft is noisier on takeoff because its engines are operating at full power. However, some manoeuvres used on landing, such as reverse thrust, can result in increased noise.

12. Why do airplanes make more noise in summer?

First of all, people are outside more often in summer and leave their windows open, so they are much more exposed to aircraft noise.

Second, because the air is hotter and less dense in summer, it provides less lift, so planes climb more slowly on takeoff and fly at lower altitudes over areas near the airport.

Atmospheric conditions like humidity, wind and cloud ceiling height can also affect noise propagation and our perception of noise.

13. How is noise disturbance near airports measured?

Like other Canadian airports, ADM mainly uses Noise Exposure Forecast (NEF) contours to measure changes in the soundscape around Montréal–Trudeau airport.

NEF contours are approved by Transport Canada and made available to municipal governments for urban planning purposes. The NEF system measures the total amount of noise created by all types of aircraft operated at an airport, based on real aircraft movements by runway and on time of day or night. The development of NEF contours requires a vast number of computer-assisted mathematical calculations. The higher the NEF level, the greater the noise disturbance.

The higher the NEF level, the greater the noise disturbance. Transport Canada recommends against undertaking new residential construction in sectors where the NEF level surpasses 30. Annoyance caused by aircraft noise may begin as low as NEF 25. It is recommended that developers be made aware of this fact and that they undertake to inform all prospective tenants or purchasers of residential buildings. In addition, it is suggested that no residential construction project proceed until the responsible authorities are satisfied that acoustic insulation features, as required, have been considered in the building design.

For the past few years, Aéroports de Montréal has been using an easier-to-interpret indicator called “total equivalent noise level” (Leq). This cumulative indicator that measures the intensity and frequency of aircraft noise reflects the average noise level during a given time period, expressed in the measurement unit dB(A). More flexible than NEF contours, Leq can also be used to study specific flights during a period of an hour, a week, etc. Real Leq can also be measured using noise sensors installed beneath flight paths around the airport periphery. Unlike NEF contours, Leq is not restricted solely to measuring aircraft noise, and can therefore be used to gauge noise from other sources, including trains and highways.

Q-13 - 2020 LEQ annuels - A.jpg


14. Air traffic is increasing all the time. Doesn’t this mean more aircraft movements (takeoffs and landings)?

In recent years, despite a significant increase in the number of passengers, the number of movements has remained relatively stable. However, this number has dropped drastically since March 2020 due to the international health crisis associated with COVID-19.

The graph below shows the trend in aircraft movements and passenger traffic at Montréal-Trudeau from 2000 to 2020.

Q-14 - Tableau mvts 2000-2020-A.jpg


15. Why was Montréal–Trudeau airport built in the middle of the city?

Montréal–Trudeau airport was built in 1940 on the site of a former horse racetrack. At the time, it was surrounded by farmland. The three photos below, taken in 1940, 1960 and 1990, show how the city gradually grew around the airport. Urban development continues today. There are high-end residential projects under construction or development near the airport, some of them under runway centre lines.




16. Isn’t there a night-flight curfew at Montréal–Trudeau?

There has never been a curfew at Montréal-Trudeau. Like all major airports and other types of transport infrastructures, Montréal-Trudeau airport is open 24 hours a day.

There are restrictions on night flights, specifically for wide-body jets weighing more than 45,000 kg (e.g., Airbus, Boeing):

  • Takeoffs: Midnight to 7 a.m.
  • Landings: 1 a.m. to 7 a.m.

Aéroports de Montréal (ADM) does have the right and the authority to grant exceptions for medical emergencies, delays beyond the carrier’s control and adverse weather conditions.

A strict internal policy applies in such cases. In particular, there are only a small number of exemptions for regular flights, and they must be supported by sound operational reasons. The exemptions are also contingent upon adherence to the noise abatement measures in force.

Note also that especially noisy aircraft cannot be granted exemptions for night flights; these include the Antonov, B727, B737 100 and 200 series, B747, DC9, DC10, Ilyushin, L101, MD 80 and MD-11.

17. Why not cease night flights at Trudeau altogether?

The airport remains open at all times to accommodate emergencies, air ambulances as well as general aviation (small private aircraft, which generally are not very noisy). In commercial aviation, night flights, including departures before 7 a.m., are vital because they provide the following advantages:

  • Return trips can be made in a single day, avoiding overnight hotel stays;
  • Final destinations with connections to other airports in Canada and the U.S. can be reached in a timely manner – for example, the 6:30 a.m. Air Canada flight to Toronto provides access to several destinations that are not served by direct flights out of Montréal–Trudeau;
  • Travellers get the most out of their holidays at sun destinations because flights leave early in the morning and return late at night.
  • Aircraft usage time is maximized, with multiple turnarounds within a 24-hour period;
  • Carriers optimize the use of their networks by co-ordinating connection schedules at their other hubs and those of their partners;
  • Companies can provide competitive rates and flexible schedules to meet passengers’ needs.
  • A competitive airport that provides international-calibre service;
  • A wide range of destinations and flight frequencies;
  • Enhances the reputation and economic growth of the Greater Montréal Region.


Movements of a typical day for Summer 2019 and Winter 2019