• The most recent noise exposure map (29 Apr 02) and impact statistics

• Revised committee print, "Areas and Residences Impacted North of the Airfield"

• Study Group memorandum, 17 Jun 02, "Recommended Noise Abatement Program"

• Study Group memorandum, 10 Jul 02, "Recommended Noise Mitigation Program"

Discussion focused on new statistics on noise impacts north of each of the two parallel runways. The new figures from the most recent modeling, especially those on housing, give the most direct and relevant account yet of the balance achieved by the proposed abatement program. The committee’s graphic depicting these results with the noise contours was commended for use in the study report.

One abatement measure for which analysis is still in progress was referred to the committee for further consideration, and was the main topic of the meeting. This was the issue of what noise abatement departure procedures should be recommended for use by air carriers in Louisville. The question was complex, because:

• Different procedures focusing on close-in or distant noise abatement for runway ends with different demographics are part of the current Part 150 program.

• Consultants had recommended these procedures be continued; but their application, and even their approval, had been called into question by airport staff.

• Carriers expressed a desire to apply a single procedure for all runways, to reduce operational complications.

The committee reviewed the results of research to clarify these elements, noting the following findings:

• Two separate noise abatement measures were put forward in the previous 150 program, because there were two separate governing publications for business and commercial traffic.

• Both measures called for "close-in" procedures to be used north, east and west of the airfield, and "distant" procedures to the south, based on population.

• Prescribed implementing steps included endorsement by airport management, publication/distribution of the procedures, and installation of signage at runway ends.

• The measure for business traffic was approved for immediate implementation.

• Because the governing FAA circular for commercial traffic was revised at about the same time the Louisville program was being acted upon by the FAA, the second measure was returned for further review and reapplication by the airport.

• Apparently no action was ever taken to implement the first measure, nor to review and reapply the second. Consequently, no formal measure is actually in force here.

• In a recent survey of procedures, nearly all responding carriers indicated they are using "distant" procedures for departures from Louisville on all runways.

• Other efforts to simplify pilot tasks have been undertaken by the committee before, recommending uniform turning points for departures, at specified navigational fixes rather than at given altitudes to the north or line crossings to the south.

Additional analysis from the study consultants arrived just before the meeting, including an expanded narrative discussing the current implications of "close-in" and "distant" noise abatement departure procedures, and an example of the simulated effect of these procedures on single-event noise contours for an MD-80 aircraft in Houston. The committee spent most of its remaining time working to apply this new information to the Louisville case, and develop a sound recommendation.

The consultant narrative helped emphasize that the effects of both "close-in" and "distant" procedures occur within a few miles of the airfield. This was an important insight, apparently not well understood in the course of the last study (perhaps because of the relative newness, and ongoing refinement, of the procedures). The committee thereafter concentrated its comparison on potential impact in the areas within about five miles.

The analysis included decision tables weighted to account for runway use, day and night, and for the range of noise contours, and giving a resulting score to each noise-abatement alternative: "close-in," "distant," or "standard" (no abatement). The committee found these tables less useful, since they didn’t account for the

• decreasing levels of noise emitted at increasing distances from runway ends

• number of households affected along various departure paths

• areas already mitigated, especially south of the airfield

An amended Houston graphic therefore gave the most explicit illustration of the relative effects of the procedures considered, though limited to a single aircraft type, at a different airport, and with a very peculiar "U-turn" departure path. The chair added a curved scale of approximate distance along this departure path to help deal with the latter problem.

This graphic indicated a very slight narrowing of the "close-in" event noise exposure contour in about the first two miles – a profile that might have some marginal effect north of the east runway, but not the west, and no effect in the south.

The "distant" procedure, on the other hand, exhibited a prominent gap in high noise exposure in the three-to-five-mile range, which would affect neighborhoods north of both runways, and could even provide some relief for neighborhoods south of the airport that, for one reason or another, have not accepted mitigation.

A "standard," or no-abatement, procedure predictably generates somewhat less noise at greater distances, where overall levels are lower to begin with. Indeed, shifting noise from higher-impact to lower-impact areas is exactly the design of the abatement procedures. The committee also recalled its earlier efforts to develop recommended flight paths that would minimize overflight of populated areas in these ranges.

Members noted further that "close-in" procedures have been cited as adding considerable wear and tear to aircraft engines because of their high initial thrust profile. Others inferred that higher levels of pollutant emissions would result from this high-thrust procedure in areas near the airport as well.

A brief teleconference with the consultant project manager served to clarify remaining points of uncertainty:

• both "close-in" and "distant" procedures involve thrust and flap settings that are different from a "standard," or no-abatement, procedure.

• the Houston example, while odd in shape, is a reasonable case for illustration, because the model used to generate it is not very sensitive to the thrust differences associated with turning along a curved path

• the model producing noise contours for the study uses a "standard" departure procedure, and would be very difficult to program otherwise

As a consequence of all this, the committee reached a comfortable consensus that the "distant" procedure is an appropriate choice for uniform application in Louisville. While "voluntary" in the sense that it must be applied by individual users, such a procedure could achieve a benefit in the three-to-five-mile range beyond that depicted in existing noise contours, without appreciable impact elsewhere.

The chair agreed to prepare recommendations for the Study Group to this effect, for presentation at the next meeting. Looking ahead to that meeting, the committee ended by considering a Meeting #7 outline of necessary presentation items, based on some twenty scope tasks still to be completed. All agreed the meeting would have to be a very busy one.

The meeting adjourned at 9:20 PM.

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