Testing in practice
Every aircraft flown on a club field should be tested before it is allowed to fly. Furthermore, any change in silencing system or propeller, let alone engine, should be tested before flying is allowed to commence, Given time, this routine changes from a source of irritation to one of considerable interest !
It is also necessary to test any aircraft that sounds noisy in the air, even if it has previously been measured as acceptable on the ground. It is only by continuous testing of all aircraft that noisy aircraft can be brought under control. Occasional bouts of noise testing do not work; although aircraft may end up quiet at the end of a purge, the situation rapidely deteriorates to pre-purge noise levels. It is only when all pilots expect their aircraft to be tested at any time that real and lasting improvements in noise emission occur.
Qualitative assessment
There are some aircraft / engine combinations that have the capacity to cause offence despite meeting the prescribed noise limit. This may be because of the way in which they are flown, because of high RPM in the air, or because of the character of the exhaust emission. These cases pose a problem as they can still lead to noise complaints despite complying with noise limits.
Such cases illustrate that we should not idolise the noise meter. The bottom line is that they could lead to noise complaints regardless of the noise meter reading, thus an alternative method of assessment may be needed.
One method is to take three independent observers (e.g. three committee members) and ask them to assess the noise emitted in flight during, say, a full throttle flypast. Each person ranks the noise as very quiet, quiet, acceptable or unacceptable. With practice, good interobserver agreement is possible, and only if the noise is ranked as unacceptable will the aircraft be grounded. Such observations should be recorded in the same way as decibel measurements.
Culture
Culture underpins many of the points discussed above. Many pilots view noise reduction as an irritating inconvenience that stops them from getting on with flying. Some will argue that noise reduction limits the performance of their aircraft, costs too much, or is a waste of time because there is no noise problem. It is necessary for the club committee to take a lead in such instances, and it is only be promoting a culture of noise reduction that attitudes are changed.
This usually takes some time, some patience, and often a little diplomacy. It is necessary if clubs are to avoid noise complaints and hence loss of flying fields. Each committee has to find its own ways of changing the culture within a club, but a few suggestions are:
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