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Aviation History
1960
1960 - 1462.PDF
302 FLIGHT,26 August 1960 Ministry of Aviation technicians monitoring jet noise in Windsor Great Park JET NOISE and Society ... their affliction, the jet airports. It can do the latter only byclosing the airports, which would be absurd. The best that the Minister can do is to attempt to keep the noise within reasonablelimits, having first defined what is "reasonable" by technical research. Technical research into aircraft noise, and humanreaction to it, is the prerequisite—and there is no doubt that British work in this field is considerable. It has been morethorough than is generally supposed; indeed, the widely held belief that the Ministry has based its noise policy wholly onAmerican (Bolt Beranek and Newman) work is not correct, as will be shown. The Ministry must accept much of the responsibility for theundoubted lack of public confidence in its efforts to regulate jet noise. The problem is not only technical: it is also one of publicrelations. Once the technical basis of a noise-regulation policy is established, good public relations can be a most effective means ofputting across that policy. It is this point that the Ministry appears to have so far overlooked. Examples of Some Misunderstandings (1) Until June 1, when the PNdb measure of noise was intro-duced, it appeared that the Ministry considered the db a satis- factory measure—notwithstanding the fact that New York hadrejected it in favour of the PNdb more than 18 months previously. This impression was given by the Minister's statement—vehem-ently contested by the residents—that a 97db limit for jets was less noisy than that of piston-engined airliners that operate at night. What the Minister did not say until much later was that he wasbasing his estimate on a 105db piston-engine level, which in PNdb terms is perfectly reasonable—except that the conditions ofthe 105db measurement have not been specified (two miles from start of take-off roll? Three miles? Four miles? Fully loadedSuper Connie or lightly loaded DC-6?). The consequent misunderstandings, in particular the belief thatthe Minister was sponsoring the misleading decibel, need not have arisen had full information been available. (2) Noise tests of BEA's Comet 4B, and of the SAS-SwissairCaravelle, were indeed carried out. But public suspicion that the Minister was merely going through the motions (an inevitablesuspicion in view of the fact that the operators concerned were already advertising and taking bookings for night jet flights) washeightened by the Ministry's refusal to publish details of the tests. What were the db measurements? Which runways? What powersettings? What weights? Suppression of this information, which is essential to a proper assessment of the validity of the tests,suggests either that something is being concealed, or that the tests were lacking in thoroughness. We have the Ministry's assurancethat neither of these doubts is warranted: one is therefore left with the impression that here is another avoidable communicationsfailure. (3) The Ministry's adoption of the PNdb, an invention of USacoustical research, was warmly welcomed as a great leap forward. What the Ministry has failed to put across is the work donechecking US work—and carrying it further—by its engineers in the National Gas Turbine Establishment in co-operation with theNational Physical Laboratory. Flight readers may recall an account of the NGTE's fascinating subjective tests into humanreactions to jet noise. The establishment had a display at the last SBAC show at which 1,600 volunteers participated in a large-scaleexperiment on the subjective effects of aircraft noise. The subjects, ranging in age from under 10 to over 70, responded to theexperiment in a way which subsequent analysis showed that the US [Bolt Beranek and Newman] "empirical method for assessingthe perceived noise level is adequate for comparison of existing types of fixed-wing aircraft." This quotation comes from theJanuary 1960 issue of the Royal Aeronautical Society's Journal* * "A Controlled Experiment on the Subjective Effects of Jet Engine Noise," by W. C. T. Copland (NPL), L. M. Davidson (NGTE), T. J. Hargest (NGTE), and D. W. Robinson (NPL). This was a paper that deserved circulation wider than amongsubscribers to a professional journal. A simplified summary would have scotched much of the public scepticism that has existedabout the technical basis of the Ministry's noise policy. (4) In adopting PNdbs, why not Ns (noys)? The N is thearithmetical analogue of the logarithmic PNdb, and as such it is much more comprehensible to non-technical people—who com-prise 99.9 per cent of the public whose interests the Ministry is, in the final analysis, protecting. If the PNdb is scientifically accept-able, ipso facto should N be acceptable. Ordinary people find 2X2 = 4 a much easier sum than 10sw X 10 301 = 10-60:i. Of course, two people might dispute that a given noise of 200Nwas twice as noisy as one of 100N. But if the empirically derived PNdb is scientifically viable, the N must be too. The point isthis: to talk in terms of 200N and 100N is better public relations than to talk in the analogous, but much more obscure, terms116 PNdb and 106 PNdb. (5) Though the Ministry has set 110 PNdb as the limit by dayit has not published the noise limit applied during sleeping hours, when a noise of 110 PNdb—or any noise—is much more disturb-ing than it is by day. For the time being, jet operations are limited Noise is recorded in the field (see map, page 301) by broadcast-quality tape-recorders (right). After processing by octave-band filte\ ampli- fier and time-recorder (top to bottom), PNdb figures are then calcu- lated. Each jet take-off takes 20 minutes to process in this way in the MoA laboratory; about 90 per cent are monitored, i.e., iflOO-plus per • j month in the summer to a small number of European operators, and the Ministryhas indicated that the night limit is less than 110 PNdb. But why cannot the actual figure be published? What is there tohide? These are a few examples of the misunderstandings that haveexacerbated an already difficult enough problem. The case for fuller public information is a strong one. The familiar phrase"public interest" often defies definition, particularly when the publication of information concerning national security is in-volved. A Minister can often evade an awkward question by saying that publication of the required information would "not bein the public interest"—and he is then exempt from further public accountability. But he can hardly say that fuller informationabout jet noise would not be in the public interest. There i: no doubt about the meaning of the phrase "public interest" in thiscontext: the public wants to know what is being done to protect family life from disruption by the greatest noise that our com-mercial civilization has ever produced, and to which society jnay not become tolerant, in the medical sense, as it did to the productsof the Industrial Revolution.
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