• Preliminary noise contour maps for each alternative, shaded for comparison with the 2005 base case

• Table of forecast daily aircraft operations by aircraft type, stage, and time of day (from Interim Report #2, Jan 2000)

• Graphics depicting runway use preferences under each alternative (from draft modeling assumptions memo, Apr 2000)

• Tables listing operations observed in ARTS data for each runway use, day and night; and tables redistributing these data to represent changed runway uses under each noise abatement strategy (new)

• Report on model excursions examining daytime-only and nighttime-only noise exposure, with accompanying contour maps (memo, Jun 16, 2000)

• Extract of ARTS data identifying selected flights opposing contraflow (originally compiled Jan 2000)

• Various notes and sketches discussing specifications for the offset approach to runway 17R

• Maps depicting flight tracks for modeling (from draft modeling assumptions memo, Aug 2000 – with offset approach added)

The committees recalled that the Study Group strategies represent varying preferences for use of the two main runways in operations north of the airport, and varying divergences of operations south of the airport. Contours estimating the impacts of these strategies clearly showed the nonlinear effects of the noise scale. Changing operations from one runway to the other can have disproportionate effects if the runway uses are not roughly the same. If the portion of operations changed in a given place is small relative to the total operations, then the effect will be disproportionately small. Conversely, if the operations changed are a relatively large portion of the total, the effect will be disproportionately large. In the preliminary runs discussed, these effects had strong implications on both ends of the runways treated by the three alternative strategies:

• In the north, a large number of operations had to be removed from the east runway to generate significant effects. Conversely, adding a small number of operations on the west runway had large initial effects, but further increasing those numbers had less and less additional effect.

• In the south, the proportion of operations available to apply different divergence options was small enough that the effects of those options were small. In particular, noise exposure to the south is heavily influenced by contraflow operations, and these operations typically demand use of both runways, where divergence is not an option but a requirement. Consequently, exercising different divergence patterns on the remaining flights didn’t have much impact on the contours.

While absorbing these observations and contemplating adjustments and refinements, a couple of immediate points arose for adjusting model inputs in succeeding runs:

• The category of operations characterized as "exceptions to contraflow" needs to be treated the same as all other operations in depicting noise abatement strategies. This presentation gave the first specific layout of such operations compiled for modeling, and, perhaps because of the informal label "exceptions", they were not shifted between runways under the different strategies along with all the rest.

• Using a fifteen-degree offset, approach and departure tracks should be aligned as nearly as possible, to minimize the ‘spread’ of noise exposure through the narrow unpopulated area northwest of the airport. This will in practice require departing aircraft to diverge at a point about a mile from the airport, rather than at an altitude of 400 feet as at present. Attendees agreed this is a reasonable procedure, and if guided by specific navigational fixes could even increase safety over the current use of only radar headings.

• The offset approach path should be checked for accuracy, in that the contours presented seem to extend further along the centerline of the west runway than they should.

The chairs undertook to accept an electronic update of the three cases to implement the above changes, and to convene another meeting to study the results. A written update from the Study Group chair to the entire Study Group was put in abeyance pending these results. The meeting adjourned at 9:40 PM.

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