The Air Navigation (Environmental Standards For Non-Part 21 Aircraft) Order 2008

Measurement system U.K.

4.—(1) The measurement system must consist of equipment equivalent to the following—

(a) A microphone, amplifier and indicating instrument having frequency response characteristics compatible with the measurement and analysis system accuracy required by sub-paragraph (2).

(b) Tripods or similar microphone mountings that minimise interference with the sound being measured.

(c) (i) Subject to sub-paragraph (ii), recording and reproducing equipment (when used) having frequency response and dynamic range characteristics compatible with the measurement and analysis system accuracy required by sub-paragraph (2).

(ii) The CAA may require that the sound produced by the microlight aeroplane must be recorded in such a way that complete information, including time history, is retained.

(d) (i) Acoustic calibrators using sine wave or broadband noise of known sound pressure level.

(ii) If broadband noise is used, the signal must be described in terms of its average and maximum root-mean-square (rms) value for non-overload signal level.

(e) A graphic level recorder or tape recorder may be used to record the noise time history.

Sensing, Recording and Reproducing Equipment for Aeroplanes

(2) (a) The sound level produced by the aeroplane must be recorded, for which purpose a magnetic tape recorder, graphic level recorder or sound level meter may be used at the option of the CAA.

(b) When a tape recorder is used it must form part of the complete system complying with International Electrotechnical Commission (IEC) Publication No. 1265 M1 or an equivalent standard.

(c) The response of the complete system to a sensibly plane progressive sinusoidal wave of constant amplitude must lie within the tolerance limits specified in Table IV and Table V for Type 1 instruments in IEC Publication No. 60651 or an equivalent standard for weighting curve ‘A’ over the frequency range 40 to 12 500 Hz.

(d) (i) The recorded noise signal must be read, over the frequency range 40 to 12 500 Hz through an ‘A’ weighting network as defined in IEC Publication No. 60651 or an equivalent standard with time weighting designated ‘S’ (SLOW) M2 .

(ii) With the agreement of the CAA, during tests with high flight speeds, the ‘F’ (FAST) time weighting may be applied to obtain the true level.

(e) (i) A windshield must be employed with the microphone during all measurements of microlight aeroplane noise.

(ii) Its characteristics must be such that, when it is used, the complete system, including the windshield, will meet the specifications of sub-paragraph (c).

(iii) Its insertion loss at the frequency of the acoustic calibrator must also be known and included in the provision of an acoustic reference level for the analysis of the measurements.

(f) (i) The overall sensitivity of the measuring system must be checked before and after the measurement of the noise level for a sequence of tests, using an acoustic calibrator generating a known sound pressure level at a known frequency.

(ii) The output of the acoustic calibrator must have been certified by a standardising laboratory M3 within 6 months of the test series.

(iii) Tolerable deviation in output from the manufacturer's stated level must be not more than 0.2dB.

Marginal Citations

M1 International Electrotechnical Commission Publications are available at www.iec.ch/.

M2 F(FAST) time weighting refers to the simulated linear response of the sound level analysers to an actual change in Sound Pressure Level (SPL) readings.{d1}{t1}The normal procedure, designated S(SLOW), takes four half second SPL readings and uses 13% from the initial half second interval, 21% from the second, 27% from the third and 39% from the fourth to calculate an equivalent SPL for a point in time at 1.25 seconds. This method is used in modern day analysis to simulate the performance of the old analogue analysers and maintain a constant data processing methodology.{d1}{t1}The F(FAST) time weighting response uses the same procedure as S(SLOW) but is performed over a short duration and is equivalent to the performance of a digital analyser. This method is sometimes used in tests with high flight speeds in order to obtain a clearer and more accurate noise profile.

M3 A “standardising laboratory” refers to a technical laboratory which has acoustic equipment calibrated against a “gold” national standard and which is licensed to calibrate other external acoustic equipment against this “gold” standard. This is a well known and documented technical term quoted in ICAO Annex 16, Volume 1, Appendix 2, Paragraph 3.5.5.