Stud­ies into the se­ri­ous ef­fects of noise on health are now be­ing ap­plied to avi­a­tion safety, with con­cern­ing re­sults, writes Michele Tydd.

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The roar of a com­mer­cial jet as it lev­els out af­ter take­off 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.”

Avi­a­tion safety re­searcher Brett Molesworth at Syd­ney’s Bankstown flight sim­u­la­tor sta­tion last week.

MICHELE TYDD is an Illawarrabased free­lance jour­nal­ist.

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