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.
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).
Emplacement des points de mesure au décollage et à l’atterrissage :
• 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).