Oct 27, 2020

These written comment to the Port of Seattle

Commission are intended to provide the detail and

documentation behind David Goebel’s spoken public

comments on 10/27/20.

The layout of the runways and distribution of the noise

monitors, specifically #11 and #12, are the central

background information:

In Southflow, arrivals land on runways 16 L/C/R. Given

their locations, monitor #11 is optimized for 16R and #12

for 16L. 16R has the large majority of arrivals in

Southflow.

Vashon Island Fair Skies

PO Box 1250

Vashon, WA 98070

http://www.vifs.org

info@vifs.org

(206)682-8638

Dedicated to restoring the pre-NextGen dispersed arrival paths and more optimized

profile descents at Seattle/Tacoma International Airport that had been in place since

the introduction of commercial aviation to the Puget Sound region, many decades ago.

Due to this distribution of arrival runways, monitor #12 correlates many fewer overflight events in Southflow. For example, in

December 2019:

Runway (Southflow)

Site

16L

16C

16R

SEA11

2344

306

31342

SEA12

4750

236

304

The flight correlation data has a variety of anomalies, including not just missed overflights, but single overflight events

registering multiple correlations, and no, not go arounds. In this latter case the spurious correlations are a few seconds apart

and have much lower intensity, combined with being few in number, mean they don’t have a significant impact on the results,

but do complicate the analysis process. In other cases, the wrong flight can be identified when there are parallel arrivals.

These don’t make a net change in LEQ, but again complicate analysis when trying to account for every single arrival.

Picking a random day in December with a small number of anomalies, Thursday December 5

, an analysis of the aggregate

impact of the overflight events intentionally excluded from monitor #12 was undertaken. This day also had zero 16C arrivals,

which are always relatively small in number, but having it zero makes the analysis easier.

On Dec 5

monitor #12 had 77 correlations (74 16L and 3 16R). In addition to the three 16R arrivals that were correlated

there were 532 16R arrivals which were intentionally excluded. Each of these excluded 16R arrivals had much lower

intensity than the 16L ones as measured by monitor #12. In order to approximate the noise level that each of these excluded

16R arrivals would have been on monitor #12, I used the 33 arrivals on December 5

that were correlated by both monitors

11 & 12 to judge what the noise intensity likely would have been. In these joint 16R correlations, the SELs (Sound Exposure

Level) on monitor #12 were approximately 9 dB lower than the same overflight measured by monitor #11.

This is an approximation as I have a day job. A rigorous analysis would use a method called “Floating Threshold” to investigate

every overflight event individually using the raw Time History data from the noise monitor. I would contend the

approximation of using these 74 joint 16R correlations is sufficiently accurate.

Taking into account these 532 excluded 16R arrivals on Dec 5th, the LEQ for monitor #12

on that day goes from ~53.4 dB to ~56.7 dB, which is about a doubling of intensity.

I do recognize that FAA regulation 14 CFR Appendix A to Part 150 - Noise Exposure Maps: Part C - Mathematical Descriptions,

Sec. A150.205(d) regarding the integration envelope for the Sound Exposure Level says:

“The time interval should be sufficiently large that it encompasses all the significant sound of a designated

event. The requisite integral may be approximated with sufficient accuracy by integrating LA(t) over the time

interval during which LA(t) lies within 10 decibels of its maximum value, before and after the maximum

occurs.”

So, you “should” include all significant events but “may” exclude those without a 10dB swing. Even using this standard, as

shown by my earlier produced video, overflight events with > 10dB swings are still excluded. I didn’t study how many events

were incorrectly excluded using the above “may” rule. It’s entirely possible that sticking with the “may” rule and performing a

Floating Threshold analysis would have resulted in a very similar LEQ deficit. I would ask the Commission to please have the

Port’s noise consultant, Vince Mestre, look at and comment on the specific numbers in this note, and not just generally

comment on the nature of noise monitoring in the abstract.

Thank you,

David Goebel

President, Vashon Island Fair Skies