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Aviation History
1969
1969 - 0098.PDF
80 FLIGHT International, li January 1969 AIR TRANSPORT US Noise Certification Proposals IN LINE WITH the Anglo-French plans for the certification by noise-levels of future jet and other transports, the US Federal Aviation Administration has now published proposed standards and regulations. A deadline of March 12 has been set for comments and a public hearing will be held before final decisions and rulings are made. The rules will apply to all new subsonic transports whatever the form of propulsion, and ail subsonic jet types regardless of category, and including some aircraft now under development. Application of the concept to supersonic transports is under study. The regulations provide for the measurement of noise at three points—approach, sideline and take-off—with limits set on a sliding scale related to weight. The limits are based on units of effective 'perceived noise level (BPNdB). This is com puted by means of a mathematical formula which takes into consideration the effects of strong tones and long duration of noise exposure in addition to noise frequency and noise level. The FAA says that "acoustical research has shown that an aircraft may receive a given noise rating based on moise level and frequency (without correction for duration and tone), but actually generates much more actual annoyance (because of durations and tones) than another aircraft that receives a similar rating, also based on noise level and frequency (with out correction for duration and tone). Thus, the FAA believes that any regulation limited to the concept of PNL [perceived noise level] could permit the continued escalation of subjective annoyance even though prescribed PNL values are fully com plied with. A correction for durations and tones must therefore be included if the objective of meaningful noise reduction at the source is to be achieved." The proposed noise limits on approach will be 102 EPNdB for aircraft weighing no more than 75,0001b. They would range up to 108 EPNdB for aircraft in the 600,0001b-and-over weight class. The measurement of approach noise would be made at a point one nautical mile from the threshold on the extended runway centreline. Sideline noise limits will also range from 102 to 108 EPNdB, with the measurement taken at the point on a line parallel with and 0.25 miles from the extended runway centreline where the noise level after lift-off is greatest. On take-off, the noise limits will be in the 93 to 108 EPNdB range and will be measured at a point 3.5 nautical miles from the start of the take-off roll on the extended runway centreline. By way of comparison, the FAA says, the noise limits prescribed are as much as 10 EPNdB less than those for the noisiest aircraft at present in service. On the logarithmic scale, a reduction of 10 EPNdB represents a halving of perceived noisiness. In addition to setting maximum noise levels., the proposals also prescribe a noise "floor" or "objective" of 80 EPNdB for all new aircraft on approach, take-off, or along the sideline. This objective should toe achieved where, the FAA says, it is "economically reasonable, technologically practicable, and appropriate to the particular type design . . . "It is recognised that this objective will not toe appropriate to many current type designs. However, this objective is important because it makes it clear to all applicants that no increment of noise above 80 EPNdB can be considered accept able, in and of itself, where it can be eliminated practically and reasonably . . . Where this goal can be reached in a given case, and can be justified as economically reasonable, techno logically practical, and appropriate to the particular type design, the FAA does not intend to ignore this potential reduction." Provision is made for "trade-offs" in the maximum noise levels to reflect the fact that total noise exposure is cumulative and that some limited "exceedances" at certain measuring points are therefore acceptable if compensated for by noise reductions at other measuring points. For example, an excess by 2 EPNdB would be allowed on take-off if compensated for by a similar reduction in the approach and/or sideline noise. Any modification, such as the stretching, of an existing air- oraft, which would require an amended type certificate or a supplemental type certificate, will also result in the application of the new noise standards if the modifications increase the noise exposure created. The FAA says that it is studying the application of the con cepts to other aircraft such as small turboprop-powered air craft and piston aircraft, VTOL aircraft (including rotorcraft), STOL aircraft, and supersonic aircraft. Also under study is the relevance of these concepts to aircraft now in service. As these studies proceed, the FAA continues, "further proposals will be issued for public comment." The proposals form the first regulatory action .taken under the recently enacted Public Law, 90-411, which grants the FAA broad authority in die control of noise, including that of with holding certification of aircraft. isiiisiiiiii
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