Aircraft noise is usually noted as a problem for people living or working near airports, but it also has a significant impact on pilots while they are flying. Aircraft noise has been cited as a causal factor in a number of aircraft accidents, usually because of the communication difficulties it creates in the cockpit. However, the effects of aircraft noise can also impact aviation safety in many other ways. Exposure to a noisy environment can increase fatigue and stress levels and has been proven to cause cardiovascular reactions and long-term hearing impairment, all of which can impair a pilot’s performance.
Aircraft noise can come from many different sources including propeller and rotor blades, engine exhaust, air intakes, aerodynamic flow, warning devices and vibrating components and panels. Each source has its own unique pitch and frequency, and each of these may cause different reactions, or have a different effect on a pilot. Depending on the noise source, working memory, decision-making capability, arousal and the ability to perform tasks may all be impacted to the point where safety is compromised.
The constant drone of a turbo-prop sits in the frequency range that stimulates sleep and fatigue. While this may be advantageous for passengers, it has serious implications for pilots, especially if it lulls them into a sleepy state. When arousal levels are low they slow down the processing of sensory information. For a pilot this is likely to have an effect on their ability pay attention to routine tasks such as scanning flight deck instruments or the external environment for other aircraft or stationary objects such as mountains, trees or power lines.
At the other end of the spectrum of frequency and pitch is the scream of a jet engine’s inlet duct, compressors and exiting exhaust gases. This type of noise is generally perceived as having a constant irritating effect which leads to an increase in stress level. The increased stress causes an increase in arousal which typically leads to a corresponding decrease in overall performance. The decrease in performance can be attributed to overloaded working memory functionality which significantly reduces decision-making capability and increases the tendency for errors to be made. Often this is because an overloaded working memory restricts its focus to what it perceives to be the most important information, and it fails to process secondary inputs. This is often the cause of controlled-flight-into-terrain accidents where the pilot is distracted by an anomaly (such as a landing gear that will not deploy to the down and locked position) and fails to maintain situational awareness and flies the aircraft into the ground.
Regular exposure to a noisy aircraft can be cumulative and has been linked to cardiovascular reactions, permanent hearing loss, and a reduction in the ability to cope with other environmental stressors in the cockpit such as heat, vibration and low humidity.