Noise and aviation safety
The roar of a commercial jet as it levels out after take-off is usually the signal to kick back and catch a movie. Studies, however, reveal it has a deeper and more disturbing significance.
University of New South Wales researchers examining the impact of noise on aircraft occupants have found that broadband engine noise of about 80 decibels at cruise altitude can cause significant pilot impairment in key areas.
It not only diminishes pilots’ recall of information from air traffic control but can also intensify fatigue, according to Dr Brett Molesworth, a senior lecturer and aviation safety researcher at the university’s School of Aviation.
“Pilots rely on information supplied by traffic controllers and others to fly the plane safely but we found that study participants did not recall between 10 and 20 per cent of messages when subjected to simulated levels of cruise noise,” says Molesworth.
“That is comparable to the recall of somebody with a .01 blood alcohol concentration and even higher – .05 – for a non-native-English-speaking pilot.”
Perceiving sound of various frequencies and decibels is unavoidable in everyday life and these latest findings are part of a growing body of evidence that noise – sound that is considered distracting and irritating – has health implications beyond hearing impairment.
Molesworth says that up until now the aviation industry has focused on noise that affects auditory health, choosing to ignore several other areas of consideration.
His team’s most recent study looks at fatigue and if it is intensified by the type of noise that is common during cruise altitude.
“Most of us are awake at 6am and as we progress through the day fatigue increases and therefore affects our performance,” says Molesworth. “We measured whether or not noise intensifies that fatigue for pilots and came up with some interesting results.”
It involved three groups of participants and two separate tests over a two-hour stretch: one group was subjected to 80 decibels of noise without any hearing protection, another to the same noise with noise-attenuating headsets, and one group was not subjected to any noise.
The memory performance in the second test of those subjected to no noise improved 20 per cent and those with the headsets improved by 11 per cent. The performance of those with noise and no protection dropped by 5 per cent.
The first test was the baseline and under quiet conditions participants should and did improve by the second round of questions because they had learnt the method of working out the answers (known in psychology as the learning effect). Molesworth says the results, however, show that noise as time went on intensified fatigue among the other two groups.
The team’s sound specialist, Marion Burgess, also identifies a problem with noise-attenuation headsets: they are only mandatory for pilots in circumstances where noise exceeds 85 decibels and are usually used haphazardly.
The fatigue study is under review and is yet to be published.
Molesworth says regulators and aircraft manufacturers could take stronger measures to reduce engine noise for all occupants, including passengers who in a separate study were found to miss about 10 per cent of the safety spiel during the aircraft’s taxiing phase, which is only about 65 decibels.
“Regulators often raise the argument that no air crash has ever been linked specifically to noise,” he says, “but that’s only because it’s not even on a crash investigator’s radar.”
However, fatigue is considered by crash investigators but not directly linked with noise. Australia’s Civil Aviation Safety Authority has guidelines to help pilots manage fatigue but they focus mainly on sleep, duty time restrictions and nutrition.
International commercial pilot Peter, who does not wish to be identified, says constant engine din figures high on his list of professional aggravations.
“We fly at about 900km/h so there’s a fair bit of air noise mainly coming around the flight deck at the front of the plane which is the first point of entry with the outside airflow,” he says. “So, yeah, there’s a lot of noise that tends to accost us.
“I can’t comment on recall but I do know that when you use headsets you find you don’t have to ask the air traffic control to repeat messages as much.”
On the issue of fatigue Peter says he finds noise wearing, particularly after long-haul flights.
Like most other pilots who use headsets for noise, he uses them only on one ear so he can hear his copilot. This means he is never totally free of engine noise.
“The noise in the cockpit tends to be more high pitched than in the cabin and you need to elevate your voice to speak to other pilots. So even that after a while becomes tiring.”
Peter says the industry could help by making noise-attenuating headsets mandatory at lower thresholds and investing in improved aircraft insulation. However, he holds little hope of change.
“Aviation is one of those price-sensitive industries. Introducing change costs money and airlines won’t add an extra $5 to a ticket to cover those costs because they know it will send people looking elsewhere,” he says.
“The industry needs to realise we work in a hostile environment. The outside air temperature at cruising altitude is usually around minus 50 degrees, we’re in the same uncomfortable clothes for up to 15 hours and, on top of that, we’ve got air noise rushing past at nearly 1000km/h, so I’d welcome anything that makes work more comfortable.”
Noise is a challenging area of health research because of its complexity. Crashing ocean waves, for example, can send many people off to sleep whereas the barely audible drip from a tap two rooms away can become intolerable.
Psychological profiling has found that introverts tend to be more affected by noise than extroverts.
For dramatic evidence of noise as a stressor, one only need to look at police reports of the violence that erupts among neighbours over barking dogs or noisy parties.
“Most people consider noise as unpleasant but are not aware of the more serious effects,” says Dr Wolfgang Babisch, who is considered one of the world’s most prominent noise epidemiologists and helped establish strong links between noise and cardiovascular disease.
In 2015, when he was senior research officer for the German Federal Environment Agency, he delivered a paper in Pittsburgh to the Acoustical Society of America that in part read:
“The evidence is increasing that ambient noise levels below hearing-damaging intensities are associated with the occurrence of metabolic disorders (type 2 diabetes), high blood pressure ... coronary heart diseases ... and stroke.
“Short-term laboratory studies carried out on humans have shown that the exposure to noise affects the autonomous nervous system and the endocrine system. Heart rate, blood pressure, cardiac output, blood flow in peripheral blood vessels and stress hormones ... are affected ...
“The long-term effects of chronic noise exposure have been studied in animals at high noise levels showing manifest vascular changes (thickening of vascular walls) and alterations in the heart muscle (increases of connective tissue) that indicate an increased ageing of the heart and a higher risk of cardiovascular mortality.”
The recently retired Babisch, when asked by The Saturday Paper if we still have much to learn about noise and its effects on the human body, says: “My short answer is, ‘Yes.’ One cannot say which exposed individuals will develop an adverse health effect.
“However, on a statistical level exposed people are at a higher risk on average. This means that relatively more events are seen in exposed than in unexposed populations after correction for other established risk factors.”
This article was first published in the print edition of The Saturday Paper on Aug 11, 2017 as "Tiring on all cylinders". Subscribe here.