Why do Airplanes Make so much Noise

It’s a bird! It’s a plane! No, really, it’s a plane. From the ground, the major airliners look like birds in cruise control, riding the thermal winds with the greatest of ease. However, the truth could not be further from the illusion. Birds are quiet and stealthy. Picture the bald eagle, descending over 2,000 feet to catch a wild rabbit, making almost no noise at all. An airplane, simply coming in to approach a runway, makes over 100 Decibels of noise. So, why do airplanes make so much noise?

Airplanes, when at cruising speed and altitude, are actually quite quiet, with the majority of the noise being made by the passing of air through the engine’s turbines into little nozzles that are pointed to the rear of the aircraft. This thrusting of air onto smaller output ports causes the aircraft’s frame to make considerable noise as well, due to the vibrations caused by the airflow, and turbulence from the prevailing winds and turbulence.

Surprisingly, the loudest portion of a flight is the landing, or approach, which is normally about 10% louder than when a flight is taking off. The approach is louder than the takeoff mainly because of the use of the turbines for reverse thrust, which drastically reduces the airplanes air-speed, while keeping it aloft and horizontal. The reverse thrust has a jarring effect on the aircraft’s structure, causing more airframe noise than at any other point of the plane’s travels. A 727 makes approximately 100 Decibels of noise while taking off, or about what a Grateful Dead concert used to produce in the 1970s, and about 110 to 115 Decibels while approaching, or landing.

For an airplane that weighs tonnes to lift off from a runway of less than 1 Kilometre in distance is quite the engineering feat. The engines that power the aircraft provide the thrust, or forward operating power, in order to allow the aircraft to attain the proper takeoff speed for it’s weight. Gravity has quite the hold on objects that are on the ground, and aircraft have to overpower this 32 feet per square inch of gravity in order to climb into the skies.

Flaps, small rudder-like pieces of the aircraft attached to the wings’ tips, also effect the plane’s ability to climb or descend, and in combination with the thrusters, the airframe noise is much greater than at any point in the flight, as air is being used as a stop-helper, which also causes more stress on the airplane’s frame, causing more noise. Also an integral part of landing an airplane, the opening and locking of the landing gear makes significant noise.

When you have the one jet landing at an airport, the noise is equivalent to a hard rock concert, near the front of the stage. When you have hundreds of planes on approach, and planes landing two per minute (as they are prone to do at the larger international airports, the noise factor is intensified and magnified as per the number of aircraft in the air.

Having grown up in the Royal Canadian Air Force (as it was known when I was a young boy), I can attest that you do get used to the noise of the aircraft, after a while. Living by an international airport, however, would be much louder, as the aircraft are generally much larger and thus require much heavier, faster, powerful engines. And, the engines are where the majority of airplane noise comes from.