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# Noise calculations supporting the Seasonal Relief QT Incentive for Grand Canyon National Park

February 24, 2015

On November 10 th , 2014 the Federal Aviation Administration ( FAA ) and the National Park Service ( NPS ) published a Federal Register Notice (FR 79(217): 66763) proposing a Quiet Aircraft Technology (QT) incentive for commercial air tour operators at Grand Canyon National Park (GRCA) to meet the requirements of the Moving Ahead for Progress in the 21 st Century Act (MAP

- 21 , P.L 112

- 141)

, consistent with section 804(c) of the National Parks Air Tour Management Act of 2000 (NPATMA. P.L.
106

- 181)

. To meet the statutory conditions in MAP

- 21 and NPATMA , the FAA and the NPS must ensure th at the cumulative impact of QT operations relieved from allocations in accordance with the seasonal relief QT incentive does not increase noise at the park

. For the proposed seasonal relief incentive, the annual noise from both QT and non

- QT commercial ai r tour flights conducted in the Dragon and Zuni Point corridors must not exceed the annual noise level of commercial air tour flights in these corridors under the current allocation system. The FAA and the NPS have modeled the annual noise of commercial a ir tour allocation s in the Dragon and Zuni Point corridors as flown with the 2012 commercial air tour fleet mix and route structure

— resulting in a noise baseline of LEQ 12 58.1 decibels (dB)

. 1 Noise will be determined to increase if the annual modeled Leq 12 of commercial air tour operations conduc t ed in the Dragon and Zuni Point corridors exceeds LEQ 12 58.1 dB in the park. This document provides an expanded technical description of th e methodology and calculations that resulted in the LEQ 12 58.1 dB refer ence criterion.

The FAA and NPS agreed that the cumulative noise impact sh ould be evaluated in terms of the sum of commercial air tour noise energy 2 occurring inside park boundaries over an entire year. This summation is intended to produce a reference c riterion for judging changes to the noise environment based on the cumulative impact of operations. This reference criterion is not intended to represent a value which may be experienced by visitors to GRCA on any particular day

. 3

To calculate commercial air tour noise energy occurring inside park boundaries, the FAA and NPS used a grid of 1224 points with 2 km spacing across the park. The agencies d etermined that the best way to ensure that the seasonal relief incentive for QT operations in the Dragon an d Zuni Corridors (DZ) does
not increase noise in the park is to compute noise at all grid points at the park, not just at grid points in the DZ. Technical experts from both agencies conferred on a methodology to work with computed noise values at 1224 grid points across the park to determine whether the cumulative impact increase s noise. T he y determined that a single number would provide the most straightforward means of measuring whether there is an increase in noise

. This number is calculated by sum ming the noise energy calculated for each year’s air tour data at each of the individual grid points and averaging it over

1 LEQ 12 stands for Equivalent Sound Level for 12 hours, which is a cumulative measure of the noise exposure of A

weighted sound levels over a 12

- hour period. LEQ 12 is one of several metrics used to evaluate air tour noise in GRCA and other national parks. A 12

- hour LEQ is used since air tour operations occur during the day, rather than
over a 24

- hour period. ANSI standard symbols would be L A,12h or L Aeq,12h (ANSI Standard S1.1

- 1994, Acoustical Terminology, section 4.14).

2 In this document, “noise energy” refer s to sums of squared, A

- weighted sound pressure values divided by the square of the reference sound pressure level of 20 μPa.

3 Cumulative noise impact is not the same criterion as the substantial restoration of natural quiet (SR NQ ). SRNQ is calculated and determined on the peak day of air tour operations using the percent time audible metric.Page 2 of 3

the whole park. Th is number , calculated annually and averaged over the park, results in a single LEQ 12 value.

The Integrated Noise Model Version 6.2 (INM 6.2) 4 w as used to quantify the amount of noise energy produced by a single flight of each type of aircraft on each air tour route used in 2012

. A program written in the R statistical environment 5 was used to multiply the INM model r esults by the amount of annual traffic allocated on each aircraft

- route combinatio n, to sum up the noise energy from DZ operations across the entire park. The spatial summation was based on noise levels modeled on a grid of the 1224 locations with 2 km spacing throughout the park. The 44,901 annual DZ allocat ions 6 were apportioned to the DZ corridor according to the reported 2012 fleet mix and route distribution by operator

. In other words, the allocated numbers were used for each of the operators u sing the 2012 reported fleet mix to distribute across the routes. 7

The first step in calculating the LEQ 12 was to sum the noise energy from all annual DZ aircraft operations spatially, across points throughout the park. This energy sum was converted to decibels (taking the base
1 0 logarithm of summed noise energy and multiplying by 10)

, resulting in a sound exposure level (L AE ) that compressed all the noise in the entire park from a year of DZ air tours into one second of exposure. For DZ allocations, this L AE equaled 135.4 dB.

Th is spatial summation of the cumulative energy produced by the total annual DZ allocation s was converted to the LEQ 12 by subtracting two values to produce an average noise value acro ss a 12 hour day. The first value divide d the noise spatially across all 1224 modeled points in the park: 10*log10(1224) = 30.9 dB

. The second value average d the noise across a 12 hour day : 10*log10(12*3600) = 46.4 dB

. The resulting final LEQ 12 value wa s 135.4

- 30.9

- 4 6 .4 = 58.1 dB

. T his LEQ 12 value is the average noise level across the entire park if a year’s worth of DZ flight allocations took place in twelve hours on a single day

. 8

In order to accurately and reliably ensure compliance with the statutory mandate that the cumulative impact o f operations under this QT incentive not increase noise at the park , the same calculation described above will be applied to each year’s air tour data. T he technical choice of a particular set of scaling fact ors does not affect the outcome since a ll future annual calculations will be conducted with the same procedures used to generate the LEQ 12 value to compare with the reference criterion of 58.1
dB

. NPATMA also provides that QT incentives must not diminish achievement of substantial restoration of natural quiet (SRNQ). In addition to the calculation and determination regarding noise increase

4 In February 2005, the Federal Interagency Committee on Aviation Noise (FICAN) recommended INM 6.2 as the best practice modeling methodology currently available t o evaluate aircraft noise in national parks. FICAN members includ e FAA, NPS, NASA, DOD. INM is used to evaluate aircraft noise in GRCA and other national parks.

5 R Development Core Team (2012). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3

- 900051

- 07

- 0, URL http://www.R

- project.org/.

6 An air tour operator may conduct the number of air tours annually that equate to the number of annual allocations held by the operator. The pro posed QT incentive would allow certain specified seasonal relief from
annual allocations.

7 Note that 40,971 of the 44,901 DZ allocations were flown in 2012, so this calculation resulted in a noise level that was 10*log10(44901/44971) = 0.4 dB greater than was generated by commercial air tours flown in DZ in 2012

. 8 This LEQ 12 value is not an average day noise level

. To produce a noise level representing a n average day at an average location in the park, th e LEQ 12 58.1 dB value would be further reduced acc or ding to the number of days in
the year . Since 2012 was a leap year, the calculation would be : 10*log10(366) = 25.6 dB

, yield ing an LEQ 12 average day of 581.

– 25.6 = 32.5 dB.Page 3 of 3

described in this document, the NPS and the FAA will ensure that SRNQ is not diminished in conformance with the defin ition of SRNQ as modified by MAP

- 21, based on the peak day of air tour operations and using the percent time audible metric.