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August/September 1995 (with an updating footnotes added in August 2002, January 2008)

Flight Deck Noise

Dr Tony Goodwin gives a detailed look at a topic that many worry about but to date has had little attention

Abstract

            Very few pilots complain of noise, either on or off the flight deck; even fewer lose their licences because of it. Those who fly noisy turbo-props or helicopters usually wear noise attenuating headsets while those in quieter commercial jets can communicate with only a light-weight earpiece over one ear, though often admitting to turning the volume up high to hear the message above the ambient noise.

            Present 'Noise at Work' regulations do not cover working on an aircraft, nor do the aviation authorities regulate either the ambient or earphone noise. When these are measured it is clear that a proportion of the pilot population is at risk of hearing damage. They should be made aware of this and a much needed debate opened up within the Industry to prevent further damage until prospective legislation to protect pilots' hearing is in place.

Introduction

            The topic of flight deck noise was selected for me by the Medical Studies Group of BALPA. It sounded about as interesting as the previous subject they asked me to write about in their "Log" magazine, which was "Diarrhoea". As few pilots had ever complained to me about noise, or appeared deaf except when asked for the fee for their examination, I asked the Secretariat at BALPA how many complaints they had received. Here are some of your comments from their files, with others interspersed throughout the text.

 

"...Clearly what has happened is that flying the B757 has

caused damage to my hearing."

 

"...I feel that perhaps we have some meaningful scientific data on the

damage the B757 is causing."

 

"...This level of noise damage on the HS748's was clearly recognised and the

pilots were issued with headsets which offered some degree of protection."

 

"...Having suffered the F27 for just over three years I am convinced that that has had

far more impact on my hearing than anything I suffered in the Jaguar."

 

Questionnaire

            I devised a questionnaire to discover how much of a problem pilots perceive noise to be. I asked them what priority they would place on improvements to their environment, mixing noise in with everything from seating to the toilet. Noise was seldom near to the top of the list. I soon abandoned this idea when it became apparent that their replies depended on the type of aircraft flown, that is whether rotary wing, turbo-prop or jet. Even different series of the same aircraft varied enormously, an early 757 flight deck being described as a flight hazard by one pilot in contrast to the relative peace and quiet described on later models.

            But noise, of course, is very subjective. In fact, I found that one of its many definitions as "A subjective response to sound that cannot be measured in physical terms". One pilot would complain that a 737 was noisy when another would say the opposite. This often related to what aircraft they had flown in the past. There is also a wide idiosyncrasy amongst individuals both to the perception of noise and to any damage that it might do to their hearing. Those who thought noise a problem I asked whether they considered its effect to be temporary or permanent. By temporary, I meant causing distraction, lack of concentration, interference with communication, stress, fatigue. A typical reply came from a pilot who complained of exhaustion after a night Athens flight in a 1-11 but who claimed to be "as fresh as a daisy" after the same trip in an MD80 which he attributed to the noise difference.

            Some complained of tinnitus and partial deafness for a short while after the flight as they drove back home in their comatose state around the M25.

 

 

"...I discovered that, on motoring home after my flying, I was unable to tolerate

having the car radio on, that what I needed was absolute silence

and that during that silence I could hear my ears singing to me."

 

            This is the so-called "temporary threshold shift", and was particularly noted at the operations and development airfield at Bedford over ten years ago, when the hearing loss, so common amongst the engineering work force there, had often improved by Monday after a weekend off.

            For those who considered that they had received permanent damage to their hearing, that is "permanent threshold shift", I looked back at their records for confirmation of when the damage was done. Sadly, because most Certifying Authorities have only been concerned with hearing within the normal range of communication, that is up to 3,000Hz, there have been few routine recordings above this level where most noise induced hearing loss would be expected to show. My retrospective study of audiograms was, therefore, disappointing. I also asked them whether it was mostly generated by the engines, the air stream, the cooling vents, the RT or the audio warning signals. Naturally, again, it depended on the type of aircraft. Turbo-prop engines, especially if positioned forward near the cockpit, were much noisier than a couple of jets near the tail. The shape of the aircraft obviously influenced the wind noise, which was made worse on older aircraft whose window seals and panels were no longer a showroom fit. Windscreen joints recently re-sealed with Mastic and covered in tank tape, which inevitably flapped loose, were said to be an incredible source of noise. A Flight Engineer on a 747 Classic demonstrated to me how noisy the escape hatch was on these aircraft by stuffing his seat cushions across it with noticeable benefit.

            The cooling vents came in for much criticism, the more complicated aircraft with larger computers apparently requiring most ventilation. Many ruses were employed by pilots to lessen this problem, the usual one being to switch off one of the ventilation packs. When the perspiring cabin crew got wise to this the engineer would remove the screw securing the control knob to the central pack. It could then be positioned to the on position while in fact turned off.

 Headsets

            But it was the headphone noise which provoked the most comment. Why should business passengers have the benefit of modern satellite communications when the pilots had to struggle with their old steam radio, they asked?

            "...are still to be found using HF equipment so out of date as to be on the verge of being dangerous. I believe the time has come for BALPA to resist the introduction of further in-cabin improvements until we are blessed with satellite communications world-wide."

            Many confessed to switching the volume of either headset or speaker up loud in order to hear the messages, especially for HF in a garbled American tongue or other form of accented English. A female voice was considered more intelligible by many, even though some 5dB quieter than the average male but, alas, the characteristic of using 20 words when two would do irritated some!

 

 

"It's no problem because I know what I'm going to hear."

How many accidents could this cause?

 

             Problems with ATC and communication between pilots have been cited in 80% of CHIRP reports. "It's no problem because I know what I am going to hear" was reported to me on many occasions. This confirms that any perceptual process depends on the experience and expectation of the listener. How many accidents could this cause? And, again, with pilots flying to age 65, perhaps with co-pilots 40 years their junior, difference in hearing acuity will be highlighted. I wonder how much conflict is caused by these disparities between pilots, and how well it is addressed on the CRM courses?

            My enquiries inevitably lead to opinions on types of headsets, and whether they cover both ears with communication via the intercom, or the much more common practice of using headsets with next to no noise attenuation and only covering the outside ear, the inside earpiece pivoted back behind the ear in the cavalier fashion started in the days of BOAC! "The present macho modus operandi", as one pilot called it.

            All the helicopter and most of the turbo-prop operators used the so-called "passive" headsets which are designed to attenuate the noise and can do so by about 24dB. They are really ear defenders with a built-in transducer and comprise an outer shell, a seal and internal damping. The design of these individual components will determine the damping effects at different frequencies. These conventional headsets do a good job in cutting out high and mid-frequency noise, but do not perform well at the low frequencies caused by wind, engine vibration and the beat of propellers. They therefore change the sound of "typical cockpit noise". The quality of the seal is vital as it tends to go hard with age and not fit properly, especially on those who wear spectacles. The final design is a compromise taking account of weight, bulk, acceptability and cost. 

            Most jet operators provide non-attenuating headsets worn over one ear, though the choice seems arbitrary. One airline's Standard Operating Procedures may specify this method, another using the same aircraft will insist on a full headset being worn. On close questioning, many pilots believe they are suffering hearing damage from the one earpiece no noise attenuation procedure, but strangely accept it as part of the job. They give a variety of reasons for preferring it, from comfort and freedom from the intercom to ease in chatting up the cabin staff.

            Of course, the main function of the headset is communication, which takes place against a background of ambient noise. Intelligibility will depend on an adequate signal:noise ratio(SNR). For average speech a signal of 6dB above the ambient noise allows for 80% comprehension, which is quite adequate for effective communication. On the flight deck twice 12dB or more is usually required and auditory warnings have to be between 15-25dB above the threshold noise. Also, the lower the SNR, the slower the response.

            Other attempts at protecting the ear include the "Active Noise Reduction"(ANR) or "Noise Cancelling" headsets. These are useful both in fast military jets where noise levels can peak under the helmet at around 250Hz but also at the frequencies below 1,200Hz that exist in large commercial airliners. We have seen that the normal "passive" headset offers little protection in this range, but the ANR set can, by subtracting the radio signal, inverting the unwanted ambient noise and the re-introducing it into the ear shell. This noise is then neutralised while allowing the radio signal to remain. Reductions of 15-30dB(A) or more are possible across the entire range of frequencies. They must have a fail safe mechanism and a good seal. Disadvantages are that they are heavier, requiring extra power, and needless to say more expensive, but this does not curb their increasing popularity amongst business passengers.

There are no specific standards for headphone noise levels, but intensity of the signal used is limited by what the ear can stand. 90dB can cause damage, 125dB pain, 160dB can rupture the ear drum. It is best to keep speech levels below 100dB; in fact speech intelligibility is best around 85dB for a given signal:noise ratio. If an SNR of 15dB is required, ambient flight deck noise must be below 85dB. If it exceeds this, then attenuation should be provided by a headset. As well as any masking noise in the range of human speech, ambient noise outside this range but within the hearing threshold can interfere with communication by delaying the rate that information can be absorbed. This is a cognitive phenomenon, which can be overcome with training and concentration, but this effort leads to fatigue.

The same principle on a larger scale is applied to the active noise reduction system being tried in the noisy Saab 2000, a high speed 50-seater turbo-prop. Here the system is based on 40 computer controlled speakers and a similar number of microphones mounted inside the cabin, and is designed to reduce the internal noise level to an acceptable 76dB. This figure has yet to be achieved despite moving the speakers and microphones around. Also it is only designed for sitting passengers, standing cabin staff are unprotected and complain of headaches. It is tempting to think that the same principle could be applied just to the flight deck but apparently it only works in a fairly constant ambient pressure and would be distorted every time the door was opened.

Microphone performance is also important for clear communication. The older dynamic and carbon mikes are now giving way to those with a gold leaf diaphragm, and by allowing the background noise to reach both sides it can cancel itself out by up to 75%.

 

The Law

            The legal requirements concerning flight deck noise are far from straightforward. The Health and Safety at Work Act includes "noise at work" regulations which make it an employer's duty to reduce the risk of noise induced hearing loss(NIHL). These regulations recognise two "action levels" at 85dB(A) and 90dB(A) and specify what action the employer must take if either are exceeded. Above the latter level ear protectors must be both supplied and worn.

            This is all fine and good except that, for some reason, aeroplanes, hovercraft and sea-going ships are excluded if moving under their own power! Concern for this extraordinary loophole caused the EC to draw up its "Physical Agents Directive" which could revoke the existing legislation and embrace 'planes and ships at any time.

            Noise up to the point of departure is covered by the present regulations, including the walk around inspection, and it amazes me that very few pilots consider using any form of ear protection at this time. The noise next to the air packs on a 747 added to that of the APUs is well into the 80dB range. A few claim to put fingers in their ears, and some use earplugs which can give primary protection of up to 25dB at low and medium frequencies. Though I am sure that this would not apply to more modern aircraft, a story repeated several times by former 1-11 pilots told of the frequent task of having to stand under the engine while running and fiddle with the constantly sticking isolation and pressure reducing valves and striking another component near the tail with the fire axe to get the thing running properly. It was described as a very noisy experience.

            One would have thought that despite its exclusion from the "Noise at Work Regulations" the Aviation Authorities would have some control over flight deck noise. But no, their regulations provide minimum, not optimum, levels and the relevant JAR 25 just waffles.

 

 

"...Could you please let me know what the industrial noise limits are for our profession?....what steps are being taken by BALPA to try and improve the situation? Are there any negotiations to have an active noise cancelling system retrofitted to current noisy aircraft?"

 

            "...I was surprised to discover recently that flight deck and cabin crews are not covered by the Health and Safety at Work Act at any stage when the aircraft is moving under its own p[ower."

 

Noise Levels

            Despite this present absence of regulation, aircraft manufacturers and airlines themselves have taken their own measurements. I have to tell you that, with a few exceptions, they have not been eager to release the figures. Nor are they mentioned in the Pilot's Operating Hand-books of  private aircraft.

            The figures depend on what stage in the flight and where in the cockpit they are taken, which should be at the pilot's ear and inside any protection worn.

             I have many anecdotal values, one of the highest from an ex-Phantom pilot on the Ark Royal who claimed 109dB inside his headset, though according to an article in last month's Pilot magazine, the average Piper or Cessna single-engined Club machine has an average noise in the cockpit of 101dB(A) in the cruise and 111dB(A) in the climb. They also quoted a Ford Fiesta at 81dB(A) when travelling fast, whatever that might mean!

            Figures kindly provided by Lufthansa appear to indicate that the 747, even the 400 series, would fail to pass the present industrial regulations if they were enforced with a noise level, including ATC dose, of 94dB(A). The A340 Airbus comes nearest at 87dB(A).

            Boeing's own figures are conveniently some 5-6dB lower for both the 747 200 and 400 series, taken at 35,000 ft and 0.85-0.87 Mach. With the addition of a minimum of 6dB for workable speech to noise ratio this just falls within the Noise at Work guidelines, though HF signals would probably put it higher.

            But if the more realistic Lufthansa addition of 13dB for ATCs noise is taken, then Boeing's figures are not acceptable either, even for the "environmentally responsible 747 400" as BA's Sir Colin Marshall calls it. Boeing mentioned that the highest noise was recorded during climb at 15,000 ft but no figure is given.

 

Audiograms

            Audiograms are the easy way to quantify hearing loss. They have in the past acquired an uneasy reputation amongst pilots and are still feared by some. They got a bad name in the RAF in the mid-1960s when some believed that any high tone hearing loss was used as an opportunity to get rid of surplus aircrew and similarly the unions in the past have been anxious lest it be used to filter the work force. Now, of course, with compensation "in the air", their results are much valued and assessment of disability is much easier for lawyers and insurers alike.

 

Loss of licence

            The number of pilots who have lost their licence due to poor hearing is surprisingly small. The CAA claims no more than one a year over the last six years. In fact, the CAA "rarely make a pilot unfit because of deteriorating hearing as they can just turn up their headsets".

            These few either would have asked to retire because of their deafness or complained of additional symptoms.

            The FAA hold a very similar view to the CAA and will allow totally deaf pilots to hold Class III certificates though with various restrictions. In a study of causes for disqualification in USAF pilots and navigators over a 2-year period in the 1980s only three were grounded for deafness.

 

 

"...The 737/200 has a high cockpit noise level...the wearing of a "Pinky" ear piece

in the early days has, I am sure, contributed to my level of deafness."

 

"...I do feel it is unsatisfactory that the turning up of the volume keeps my licence valid

regardless of the long term consequences."

 

 

            How can these levels of noise affect the pilot during his working life? Here is the case of a 52 year old captain who, after eight years on a 747 Classic had to retire through tinnitus, hyperacusis and noise induced hearing loss. Hyperacusis causes pain at certain frequencies from sound pressures as low as 85dB(A) which we have seen is around the noise level of the 747's flight deck. This pain can last for fifteen hours after a flight. The hearing loss in the left ear of a captain prevents safe ATC comprehension and the tinnitus brings fatigue.

            He considers the ATC noise in a single headphone over his left ear on top of high environmental noise to be the cause of his difficulties and believes his employer to have been negligent in failing to take heed of developing knowledge on the subject of flight deck noise and not taking the necessary precautions. He calculates that at least 10% of the over fifties on his fleet should be suffering significant Noise Induced Hearing Loss and suggests that changes in procedures and minor improvements to equipment, together with dissemination of information to its workforce, would save the hearing of that percentage of its pilots and thus the waste of expensively trained personnel who should legitimately receive compensation.

 

Conclusions

            What then can be done to protect the future generation of pilots and prevent further damage to those already flying?

            It would be handy if those with an idiosyncracy to noise could be weeded out at initial selection.

            Perhaps frequent monitoring of hearing in the early months of their training would help, for there is a theory that the temporary hearing loss from one day's exposure equates to the permanent loss that is seen ten years later after the same abuse. And pilots towards the end of their careers, which can now be extended to age 65and give a possible 45 years of exposure to flight deck noise, might also benefit from more regular monitoring, especially senior captains who tend to bid for the more lucrative longer flights. I have not asked, but wonder whether the various Pilots' Associations would now be so resistant to such a policy? Should the pilot with deteriorating hearing be encouraged to continue flying by turning up the radio sound, or should he be protected from himself and grounded?

            Aircraft manufacturers should reduce the noise on the flight decks from their present levels. If the acoustic characteristics of a concert hall can be predicted by computer, so can a flight deck. There will always be increasing pressure from environmentalists for quieter engines, and this can only benefit the flight crew as well.

 

 

Should the pilot with deteriorating hearing
 be encouraged to continue flying by turning up the sound,

or should he be protected from himself and grounded?

 

 

            Airbus Industrie responded to complaints of high flight deck noise on the A310 and we now have a nice quiet A340 where the first class passengers can hear what the crew in the galley are saying about them. Boeing at last have apparently taken heed of changing knowledge and requirements and incorporated them into the new 777. Moving the engines further away from the cockpit can also help the crew, though possibly not the tail end passengers! Modern materials which are both light and yet effective sound insulators could be used to make retrospective hush kits for older aircraft.

            Attention to external fittings such as windows and hatches could always be improved to reduce the wind noise. We will all have noticed how much quieter a modern car is compared with ten years ago, and this is travelling at a fraction of the aircraft's speed. Air conditioning fans and vents could be better designed and insulated, and though more computers seem to be finding their way onto the flight deck, the better chips now available should require less cooling with its attendant noise.

 

"...information on the levels in B737 aircraft...so that BALPA members

can be supplied with the ammunition needed to take on their employers

and be issued with the appropriate protective headsets."

 

           

           With a less noisy flight deck, both audio warnings and RT will not have to be so loud, but where the ambient noise level is still too high, then proper headsets providing passive or active attenuation should be insisted upon despite some pilot's protestations. This should include the walk around. Meanwhile it is high time that the quality of radio transmission was improved as the technology is readily available. Replacement of HF by satellite VHF and provision of data link should now be in common usage. Sooner or later the pressure being put on manufacturers and operators to limit external aircraft noise will be imposed by legislation to include the flight deck. This will not only impose massive costs on the airlines to hurriedly update their equipment, but also make them liable to an avalanche of claims from pilots whose hearing has been damaged in the past.

            Perhaps what is required most of all at this time is a change of attitude towards noise, a change of attitude by pilots themselves to protect their own hearing more than they do now and to challenge their present SOPs if they consider them inadequate.

            Finally, the airlines themselves hopefully will take heed and open up a much needed debate on the subject before further damage is done, needless expense and suffering involved, and safety jeopardised. Certainly a willingness to educate and disseminate information at this time would be encouraging but the responsibility should be shared by employer and employee.

             I realise that there appear more pressing topics, such as flight time limitations, to be discussed at present, but on the flight deck a time-bomb is ticking for those who can hear it!

PS

            I should also add that the views I have expressed are my own and not necessarily shared by BALPA.

*********

            This article is adapted from a presentation I made at the Royal Aeronautical Society in April 1995. All readers must have some opinions on the subject, so please put pen to paper(or fax I suppose these days) and let me have them.

            My thanks for help and information from:

                        Dr Ken Edgington and his crew(CAA Medical Division)

                        Dr Michael Bagshaw(British Airways)

                        Dr John Merritt(Cathay Pacific)

Dr Lutz Bergau(Lufthansa)

Air Commodore Peter King(formerly ENT Consultant to the RAF)

Dr Flindell(Institute of Sound and Vibration, Southampton University)

Len Beirne(Health and Safety Executive)

Mark Pauton and Mitch Barnes(Headset Services, Haywards Heath)

Keith Perrin(CAA Flight Test Department)

Also

            Pilot, New Scientist, Flight International, Aviation Space and Environmental Medicine journals, and over five hundred pilots who hoped they were getting a discount on their medicals by telling me what it was all about.

Update August 2002

Several changes have taken place since that presentation seven years ago. 

Firstly several airlines, most notably BA, have tried to introduce ANR headsets with varying degrees of acceptance.  The most common problem has been that a combined active and passive headset has been provided which is not only heavy and uncomfortable but requires communication through the intercom.  Pilots have objected to this for a variety of reasons from not being able to hear the engines or signals to not realising when the cabin staff have come onto the flight deck with their next course of dinner.  A few have also mentioned a feeling of pressure on the eardrums.

A result of this has been a hotch-potch of SOPs which usually forbid the pilot to use the ANR sets when the flight deck is noisy, particularly in the climb, when the old one ear on, one ear off practice renders them useless for hearing protection.

The answer would seem to lie in providing the lighter sets with no passive noise reduction shell but just a foam pad fitting over each ear.  These cut down the low frequency rumble from engines, cooling packs, etc., which is responsible for the noise induced hearing loss, yet allow conversation and signals to be heard without the need to use the intercom.

The second change is that at last a European Directive will be passed sometime this year which will not only bring the 'action levels' in the Noise at Work Regulations down to 80/85 dB(A) but will also include moving aircraft and ships.  BA found that the noise from the standard issue 'open ear' style headset exceeded 80dB(A) on 80% of flights and 85dB(A) on 30-40%.  Once passed, legislation in each country must be introduced within three years.  At that time it is probable that there will still be many aircraft flying which exceed the limits.  It is not yet known how the Directive will be implimented, but probably guidelines will be produced by the HSE/DTLR with the CAA to audit the airlines compliance.

We have not heard the last of Flight Deck Noise!

Dr S A Goodwin

Update January 2008
 
The Control of Noise at Work Regulations 2005 came into force on the 6th April 2006. The new regulations implement the European Union's Physical Agents (Noise) Directive within Great Britain. That Directive was dated 2002 and each state had three years to implement it. 

The new regulations bring significant changes to the actions that were required by employers and employees under the previous Noise at Work Regulations 1989.  Employers now have extra responsibilities, and noise exposures and level limits are lower. The Regulations cover not only the obviously noisy industrial premises and construction sites, but virtually all workplaces with few exceptions. Work onboard aircraft is now covered and every airline should have conducted a risk assessment and taken appropriate action if a problem was found. In the case of flight deck crew this would usually be by the provision of Active Noise Reduction(ANR) headsets together with appropriate standard operating procedures(SOPs) for their use.. If in doubt about hearing protection, you could approach your employer and ask how the noise risk assessment was conducted(see the article above plus the Regulations) and ask for the results.

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Airport Medical Services Limited
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