Old Sky Harbor Flight Paths Had Less Impact, Data Shows

Phoenix is once again throwing its support behind the pre-September 18 departure flight paths out of Sky Harbor Airport. The decision comes after the city Aviation Department modeled multiple alternatives, calculated the noise impact each would have, and proved that the original paths are in fact the least disruptive options.

At a special City Council meeting late last week, Chad Makovsky of the Aviation Department, and an aviation consultant, Tom Cornell, presented the results of their modeling experiment. Through very telling visuals, they explained how the changes the FAA has proposed in recent weeks would result in more noise for residents.

See also: -Phoenix May Sue the FAA After Agency Allegedly Lied in Letter to City -Sound and Fury: Frustrated Phoenix Residents Are Roaring Ever Since the FAA Changed Sky Harbor Flight Paths

Noise is measured in decibels, and a sound of about 75 decibels is said to interfere with normal conversation and pose "a significant impact." The Aviation Department team used information about the projected altitude and speed of planes to create a line around areas that would receive at least 75 decibels of noise for each proposal. They then put that line on top of a population density map, which allowed them to calculate how many people would be disrupted by airplane noise.

If this sounds confusing, consider the example below. It compares the old northwest flight path to the new one.

You are looking at a population density map of Phoenix, in which the darker-blue squares are higher density areas, and the white areas are industrial or otherwise mostly uninhabited areas. The orange oval represents the area of the city that received 75 decibels or more of noise when the old flight path was in place, and the green line represents the areas that get that level of noise from the current flight path. As is noted on the map, the population affected by the new flight path is 68 percent higher than the pre-September 18 path.

Now look at this example, which includes a third line representing the area that would be affected by one of the FAA's proposals--termed NW5 Corridor.

If you consider how much blue is inside of each oval, it becomes clear that this path would affect a lot more people than the old flight path. And in fact, according to the Aviation Department's calculations, it would have 126 percent greater impact.

The Aviation Department also modeled the FAA's proposals for changing the Southwest flight path. Here's the Previous SW Corridor compared to the current one:

It's easy to see how it affects far more people.

And here is a model depicting the old SW path, the current one, and one of the FAA-proposed alternatives:

Again, it's easy to see how this affects more people than the old path.

The takeaway from the presentation at City Council last week was that the old NW and SW flight path corridors resulted in far fewer people affected by airplane noise.

"It was intuitive that the city-proposed models would be the best," Makovsky said, "but this helped us to see it that it would be the case."

The models that the Aviation Department created are based on proposals the FAA designed earlier this month, and gave to the "PBN working group" members on April 7. (The working group is a team comprised of FAA officials, airline representatives, aviation technicians, and three representatives from the city of Phoenix. The FAA suggested forming the group in February to collaborate on finding a solution for the Sky Harbor flight path problem. The group has met three times.)

In the proposal, the FAA outlined 14 alternatives, and provided some data for the two paths it preferred. "They did no modeling for any of the other [12] alternatives, except to say that they didn't meet their safety and efficiency standards," Makovsky tells New Times. "This tells me that they did not take those options very seriously."

The following day, the Aviation Department requested that that FAA consider the other options more carefully and produce models for them as well. The FAA said it would, but on Friday April 10, only delivered what's called "TARGETS data" for some of those other alternatives. (TARGETS, which stands for Terminal Area Route Generation and Traffic Simulation, is a tool that combines all sorts of visual and mathematical data to help those designing flight paths.)

It wasn't what the city had expected or asked for, but it did include information about "where a plane would be at any given time and how high it would fly," Makovsky explains, "which allows you figure out how loud a plane will be at any given point."

The Aviation Department used this data to create the noise models you saw above. But unfortunately, as telling as these models are, Makovsky says, the FAA is unlikely to give them much weight because the agency uses a different sound metric to determine what constitutes a "significant noise impact."

The FAA measures noise by Day-Night average sound level, which, like it appears, is an average of all the noise over a 24-hour period. The Aviation Department used Single Event Sound Equivalent Level, which measures the impact of a single sound, and does a much better job depicting how we as humans actually perceive airplane noise. (We hear individual planes flying over our homes; we don't perceive sound in 24-hour period averages.)

Still, the city plans to give the FAA these models when it sends a response to the damning letter it received last week from the agency. The letter stated that the city has not participated fully in the process of correcting the flight paths, a contention City Councilman Michael Nowakowski called "a lie."

For months, the FAA has said it values the city's input and that it would evaluate its proposals with great consideration in the PBN working group. But last week the city learned that the FAA leadership dictated exactly what adjustments they would approve. Specifically, the agency would not agree to any changes that required a new federal action, meaning anything that requires safety or environmental assessments.

"The working plan that you received was the result of the working group wanting to propose to you what they wanted," said former Congressman Ed Pastor, who represented the city in the PBN group. "It was not a negotiation," he added.

Supported by the information from the noise-measurement models, the City Council unanimously voted to "discontinue engagement in the PBN working group" and "renew its request to the FAA to revert to previous flight paths."

"We think it's now time for the city to take the lead [on fixing the flight paths] rather than waiting for the FAA," Makovsky said.

Editor's Note: A previous version of this story said the FAA provided noise-modeling for two of the 14 alternatives it proposed. It only provided TARGETS data.

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Miriam is a staff writer at Phoenix New Times.
Contact: Miriam Wasser