FAQ

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.

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.

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.

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 as noisy as 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. With a few 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.

Virtually all passenger transport aircraft operating out of Montréal–Trudeau are certified Chapter 3 or Chapter 4. Where general aviation is concerned, there are still a few small Chapter 2 aircraft, but they are exceptions. Chapter 2 aircraft equipped with noise mufflers known as "hush kits" represent a very small percentage of the fleet operating in Montréal-Trudeau.

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. Note that this configuration has remained unchanged since 1958.

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 exists a priority runway system for night operations.

The tables and graphics below show the frequency of use of the various runways at Montréal–Trudeau from 2006 to 2017:

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 915 metres (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.

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.

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 from Runways 24L and 28, and land on 24L and 24R.

If the winds are from the northeast, planes take off and land in the opposite direction, on Runways 06R and 06L.

Runway 10 is used when there are strong crosswinds, or as an auxiliary runway.

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

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.

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.

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, if 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.

Increasing passenger traffic does not necessarily equate to more aircraft movements: airlines can use larger aircraft, or increase their passenger occupancy rates.

The graph below shows the trend in aircraft movements at Montréal-Trudeau since 2005.

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.

There has never been a curfew at Montréal-Trudeau. Like all major airports and other types of airport infrastructures, Montréal-Trudeau airport is open 24 hours a day. However, there are certain restrictions on night flights, specifically on flights by wide-body jets weighing more than 45,000 kg (e.g., Airbus A320, Boeing 737).

Takeoffs: Midnight to 7 a.m.


Landings: 1 a.m. to 7 a.m.

Aéroports de Montréal (ADM) does, however, have the right and the authority to make 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 (four departures per day on average), 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.

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:

FOR PASSENGERS

• 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 32 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.

FOR CARRIERS

• 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.

FOR THE MONTRÉAL COMMUNITY

• We have a competitive airport that provides international-calibre service;
• Montrealers can enjoy a wide range of destinations and flight frequencies;
• Round-the-clock use enhances the reputation and economic growth of the Greater Montréal Region.

Today's traffic

The vast majority of aircraft movements takes place during the day.