Clark County Department of Aviation 

Appendix D. Helicopter Noise Analysis 

D.1 General Characteristics of Helicopter Noise 

Helicopter noise originates from three components of the helicopter: the rotors, engine, and 

transmission. 

Generally speaking helicopters are equipped with two rotors. The main rotor is located on the top of 

the cabin and is used to generate lift. The other rotor (tail rotor) is located in the tail and is used to 

produce a sideways force that prevents the body of the helicopter from rotating and is also used to 

steer the helicopter. Two types of helicopters – the AS350 and EC130 are used by Grand Canyon 

tour operators based in Clark County. Almost all helicopters are equipped with one of two types of 

tail rotors: a conventional tail rotor or a Fenestron tail rotor. By nature of its construction, the 

Fenestron tail rotor is quieter than the conventional tail rotor. The AS350 is equipped with a 

conventional tail rotor and the EC130 is equipped with the Fenestron tail rotor. 

Power is transferred to the rotors from the engine via a main gearbox. The engine’s revolutions per 

minute (RPMs) are reduced from thousands to hundreds by increasing the torque and slowing the 

rotation to an acceptable level for the rotors. Noise generated by the engine depends on the 

type/model of engine powering the helicopter. The transmission drives the mast, which provides 

direct rotation to the rotors. Noise generated by the transmission depends on the type/model of 

engine and transmission powering the helicopter. 

D.2 Definition of Noise 

Loudness, measured in decibels (dB), is the most commonly used characteristic to describe noise. 

The A-weighted decibel (dBA) is used in aircraft1

 noise analyses because it incorporates a 

frequency-dependent rating scale that more closely associates sounds and sound frequencies with the 

sensitivity of the human ear. Some common sounds on the dBA scale, relative to ordinary 

conversation, are listed in Table D-1. As shown in the table, the relative perceived loudness of a 

sound doubles for each increase of 10 dBA, although a 10-dBA change corresponds to a factor of 10 

in relative sound energy. Generally, sounds with differences of 2 dBA or less are not perceived to be 

noticeably different by most listeners. A noise event produced by a helicopter flyover is usually 

characterized by a buildup to a maximum noise level as the helicopter approaches, and then a 

decrease in the noise level through a series of lesser peaks or pulses after the aircraft passes and the 

noise recedes. 

As used in report, “aircraft” includes helicopters. 

Final EA for a Southern Nevada Regional Heliport D-1 December 2008 

Appendix D 

1 
Clark County Department of Aviation 

Table D-1 

Common Sounds on the A-Weighted Decibel Scale 

Sound Level Relative Loudness Relative Sound 

Sound (dBA) (approximate) Energy 

Rock music, with amplifier 120 64 1,000,000 

Thunder, snowmobile (operator) 110 32 100,000 

Boiler shop, power mower 100 16 10,000 

Orchestral crescendo at 25 feet, noisy 90 8 1,000 

kitchen 

Busy street 80 4 100 

Interior of department store 70 2 10 

Ordinary conversation, 3 feet away 60 1 1 

Quiet automobiles at low speed 50 1⁄2 0.1 

Average office 40 1⁄4 0.01 

City residence 30 1/8 0.001 

Quiet country residence 20 1/16 0.0001 

Rustle of leaves 10 1/32 0.00001 

Threshold of hearing 0 1/64 0.000001 

Source: U.S. Department of Housing and Urban Development, Aircraft Noise Impact—Planning Guidelines for Local Agencies, 1972. 

Prepared by: Ricondo & Associates, Inc., April 2008 

D.3 Noise Analysis Methodology 

The methodology used for this helicopter noise analysis included the: (1) use of noise descriptors 

developed for helicopter noise analyses, (2) application of a computer model that provides estimates 

of helicopter noise levels, and (3) development of basic data and assumptions as input to the 

computer model. 

D.3.1 Noise Descriptors 

Noise is measured using a variety of scientific metrics. As a result of extensive research into the 

characteristics of aircraft noise and human response to that noise, a standard system of descriptors 

has been developed for use in aircraft noise exposure analyses. These descriptors, as used for this 

helicopter noise analysis, are described in the following subsections. 

D.3.1.1 A-Weighted Sound Pressure Level 

The decibel is used to describe sound pressure level. A-weighting approximates the human ear’s 

sensitivity to sounds of different frequencies. Without this filtering, calculated and measured sound 

levels would include sounds that the human ear cannot hear, such as dog whistles (high frequency) 

and sounds made by large buildings with changes in temperature and wind (low frequency). 

D.3.1.2 Maximum A-Weighted Sound Level 

The maximum A-weighted sound level (Lmax) is the loudest part of a noise event, measured in 

decibels. As an aircraft overhead passes an observer, the noise increases to a maximum level and 

then decreases as the aircraft passes. Some sound level meters measure the maximum, or Lmax, level. 

Final EA for a Southern Nevada Regional Heliport D-2 December 2008 

Appendix D 
Source: Ricondo & Associates, Inc. 


Prepared by: Ricondo & Associates, Inc., April 2008 


Clark County Department of Aviation 

D.3.1.3 Equivalent Sound Level (Leq) 

Leq is a standard measure of sound energy averaged over a specified time period. This metric 

indicates the constant sound level in decibels which is equivalent to the amount of sound energy 

produced by a series of events having fluctuating sound levels during the specified time period. 

D.3.1.4 Sound Exposure Level 

Sound exposure level (SEL) is a time-integrated measure, expressed in decibels, of the sound energy 

of a single noise event at a reference duration of one second. The sound level is integrated over the 

period that it exceeds a threshold. Therefore, SEL accounts for both the maximum sound level and 

the duration of the sound. The SEL for a particular aircraft noise event is a numerically higher value 

than the (Lmax) for the same event. This is because the SEL consolidates the energy of the entire 

noise event into a reference duration of one second. The SEL is not “heard”, but is a derived value 

used for calculation of cumulative aircraft noise exposure as defined by the DNL. SELs for aircraft 

noise events depend on the location of the aircraft relative to the noise receptor, the type of operation 

(landing, takeoff, or overflight), and the type of aircraft. The SEL concept is depicted on 

Exhibit D-1. 

Exhibit D-1 

Sound Exposure Level Concept 

Final EA for a Southern Nevada Regional Heliport D-3 December 2008 

Appendix D 
Clark County Department of Aviation 

D.3.1.5 Background Sound Level (L90) 

L90 describes the noise level exceeded 90 percent of the time during the sample period. L90 is useful 

for describing the background (or residual) noise level in the absence of any easily defined noise 

events, such as those caused by occasional traffic, barking dogs, or aircraft overflights. 

D.3.1.6 Day-Night Average Sound Level 

Day-night average sound level (DNL) is a method used to describe the existing and predicted 

cumulative noise exposure from aircraft operations in the vicinity of an airport or a heliport. The 

DNL is expressed in dBA and represents the time-weighted average noise level over a 24-hour 

period. The DNL is used to estimate the effects of specific noise levels on land uses. The 

U.S. Environmental Protection Agency (EPA) introduced the DNL metric in 1976 as a single number 

measurement of community noise exposure. The Federal Aviation Administration (FAA) adopted 

DNL as the noise metric for measuring cumulative aircraft noise under Title 14, Code of Federal 

Regulations, Part 150 (14 CFR Part 150), Airport Noise Compatibility Planning. DNL has also been 

adopted for measuring cumulative noise exposure by several other government agencies, including the 

Department of Housing and Urban Development, the Veterans Administration, the Department of 

Defense, the Coast Guard, and the Federal Transit Administration. DNL is widely accepted as the best 

available method to describe aircraft noise exposure and is the noise descriptor required for use in 

aircraft noise exposure analyses, land use compatibility planning, environmental assessments, and 

environmental impact statements for airport/heliport improvement projects. Although additional 

noise metrics may be used to characterize aircraft noise and environmental impacts, neither Clark 

County nor the State of Nevada mandates the use of metrics other than DNL. 

In calculating DNL, for each hour during the nighttime period (10:00 p.m. to 6:59 a.m.), sound levels 

are increased by a 10-decibel-weighting penalty before the 24-hour value is computed. The 

weighting penalty accounts for the more intrusive nature of noise during nighttime hours. 

DNL is expressed as an average noise level on the basis of annual aircraft operations for a calendar 

year, not on the average noise levels associated with different aircraft operations. To calculate the 

DNL at a specific location, the SELs at that location associated with each aircraft operation (landing 

or takeoff) are determined. Using the SEL for each noise event and applying the 10-decibel penalty 

for nighttime operations as appropriate, a partial DNL is then calculated for each aircraft operation. 

The partial DNLs for each aircraft operation are added logarithmically to determine the total DNL. 

The logarithmic addition process, whereby the partial DNLs are combined, can be approximated by 

the following guidelines: 

Adding the noise from a relatively quiet event (60 dBA) to a relatively noisy event (70 dBA) results 

in a value of 70 dBA because the quieter event has only one-tenth the sound energy of the noisier 

Final EA for a Southern Nevada Regional Heliport D-4 December 2008 

Appendix D 
Clark County Department of Aviation 

event. As a result, the quieter noise event is “drowned out” by the noisier one, and there is no 

increase in the overall noise level as perceived by the human ear. 

DNL is used to describe existing and predicted noise exposure in communities in an airport/heliport 

vicinity based on the average number of daily operations over the year and the average annual 

operational conditions at the airport/heliport. Therefore, at a specific location near an 

airport/heliport, the noise exposure on a particular day is likely to be higher or lower than the annual 

average noise exposure, depending on the specific operations at the airport/heliport that day. 

D.3.2 Integrated Noise Model 

The Integrated Noise Model (INM) was developed by the FAA, and is the computer model required 

for use in developing aircraft/helicopter noise exposure maps. The INM contains aircraft operational 

and noise data in a database that reflects average aircraft operating conditions. The INM was 

originally designed for modeling noise from fixed-wing aircraft. However, with the introduction of 

Version 7.02

 of the INM, the FAA incorporated the noise modeling capabilities of its Helicopter 

Noise Model (HNM). INM Version 7.0 is the latest accepted state-of-the-art tool for determining the 

total effect of aircraft noise at and around airports and heliports, and is the model that was used to 

determine potential helicopter noise impacts for this analysis 

Because the DNL is fundamentally based on the noise levels produced by individual aircraft 

operations, selection of appropriate aircraft-type designations from the INM database is of critical 

importance. The INM Version 7.0 database contains both of the helicopter types that are used by 

Grand Canyon tour operators based in Clark County. Those helicopter types are designated within 

the INM database as the SA350D (AS350) and the EC130. The SA350D and EC130 helicopter types 

were used without modification to model helicopter noise levels for this analysis. 

D.3.2.1 DNL and Noise Exposure Ranges 

A noise exposure value of DNL 65 was used as the criterion level for the noise analysis. Two 

specific ranges of noise exposure were estimated: (1) DNL 65 and higher and (2) DNL 60 to 65. 

DNL 65 and higher is the FAA’s standard threshold for land use compatibility planning purposes in 

areas surrounding a heliport or airport. Although the FAA considers aircraft noise exposure lower 

than DNL 65 to be compatible with residential land uses, persons residing outside the DNL 65 noise 

exposure area may still be annoyed by aircraft noise. However, Clark County agencies use 

information regarding noise exposure between DNL 60 and DNL 65 for local planning purposes and 

therefore DNL 60 noise contours are depicted on exhibits in this EA. 

D.3.2.2 The DNL Descriptor 

The validity and accuracy of DNL calculations depend on the basic information used in the 

calculations. For future heliport activities, the reliability of DNL calculations is affected by a number 

of variables: 

x Future aviation activity—the number of helicopter operations, the types of helicopters in the 

fleet mix, the times of operations (daytime and nighttime), and helicopter flight tracks—are 

estimates or forecasts, the achievement of which cannot be assured. 

x Although new helicopter types may be introduced in the future, current models were used as 

input to the INM to estimate future activity. 

Final EA for a Southern Nevada Regional Heliport D-5 December 2008 

Appendix D 
Clark County Department of Aviation 

x The noise descriptors used as the basis for calculating DNL represent typical human response 

(and reaction) to aircraft/helicopter noise. Because people vary in their responses to noise 

and because the physical measure of noise accounts for only a portion of an individual’s 

reaction to that noise, DNL can be used only to obtain an average response to aircraft noise 

that might be expected in a community. 

x Single flight tracks used in computer modeling represent a wider band of actual flight tracks. 

These uncertainties aside, DNL mapping was developed as a tool to assist in land use planning 

around airports/heliports. Mapping is best used for comparative purposes rather than to provide 

absolute values. DNL calculations provide valid comparisons between different potential conditions, 

so long as consistent assumptions and data are used for all calculations. 

Thus, sets of DNL calculations can show anticipated changes in aircraft/helicopter noise exposure 

over time, or can indicate which of a series of simulated situations would be better, and generally 

how much better, from the standpoint of noise exposure. However, a line drawn on a map is not 

meant to imply that a particular noise condition exists on one side of that line and not on the other. 

DNL calculations are a means for comparing noise effects, not for precisely defining them relative to 

specific parcels of land. 

Nevertheless, DNL contours can be used to (1) highlight an existing or potential aircraft noise 

problem that requires attention, (2) assist in the preparation of noise compatibility programs, and 

(3) provide guidance in developing land use controls, such as zoning ordinances, subdivision 

regulations, and building codes. DNL has been, and is still, considered to be the best methodology 

available for depicting aircraft/helicopter noise exposure. 

D.3.2.3 Graphic Representation of DNL 

Contours are lines on a map that connect points of equal DNLs, much like topographic contour lines 

are drawn on a map to indicate ground elevations. For example, a contour is drawn to connect all 

points exposed to DNL 65; another may be drawn to connect all points exposed to DNL 70; and so 

forth. Generally, noise contours are plotted at 5-DNL intervals. Noise contours were developed for 

this analysis in conformance with FAA guidelines included in FAA Orders 5050.4B and 1050.1E and 

14 CFR Part 150. For this analysis, the INM was used to produce DNL 65 and DNL 60 helicopter 

noise exposure contours. 

D.3.3 Basic Data and Assumptions for Developing Noise Exposure Maps 

The primary data required to develop helicopter noise exposure maps using INM Version 7.0 are: 

x The existing and forecast number of helicopter operations, by helicopter type, and with 

daytime or nighttime flight characteristics. 

x Operational information, including use of the runways or touchdown and liftoff areas, 

location and use of flight tracks (the paths that pilots fly to arrive at and depart from the 

airport or heliport), departure profiles, and existing noise abatement procedures. 

Final EA for a Southern Nevada Regional Heliport D-6 December 2008 

Appendix D 
Clark County Department of Aviation 

D.3.3.1 Helicopter Operations 

To determine existing and projected noise exposure, helicopter operations associated with the 

average day of the year are used in the INM. Helicopter operations data for an average day in 2004 

were used to represent existing conditions in this environmental assessment. The 2004 average 

annual day condition is based on actual helicopter operations data collected by AirScene2

. Forecasts 

of operations for the average day in 2011 and 2017 were derived from the annual forecasts presented 

in Chapter III of this EA. 

Existing and forecast levels of helicopter operations under the Proposed Action are presented in 

Table D-2. Existing and forecast levels of helicopter operations under the No Action alternative are 

presented in Table D-3. As shown in Table D-2, the number of Grand Canyon tour departures at the 

Heliport site under the Proposed Action is projected to be 29,500 in 2011 and 37,300 in 2017. It was 

assumed that the operators of Las Vegas Strip tours would not relocate to the proposed Heliport site 

from McCarran. Las Vegas Strip tours would continue to be accommodated at McCarran under the 

Proposed Action – 8,400 annual tour departures in 2011 and 9,100 annual tour departures in 2017. 

Under the Proposed Action there would be 9,800 Grand Canyon tour departures at McCarran in 2011 

and 12,400 annual Grand Canyon tour departures in 2017. Under the Proposed Action it is 

anticipated that some helicopter operations, both Grand Canyon tours and Las Vegas Strip tours, 

would be accommodated at other locations in the region (11,100 annual tour departures in 2011 and 

15,600 annual tour departures in 2017). These helicopter movements were not assessed or evaluated 

in this environmental assessment. 

As shown in Table D-3, the number of Grand Canyon tour departures at McCarran under the 

No Action alternative is projected to be 29,500 in 2011 and 37,300 in 2017. Las Vegas Strip tours 

would continue to be accommodated at McCarran under the No Action alternative – 8,400 annual 

tour departures in 2011 and 9,100 annual tour departures in 2017. It is anticipated that some 

helicopter operations, both Grand Canyon tours and Las Vegas Strip tours, would be accommodated 

at other locations in the region under the No Action alternative (20,900 annual tour departures in 

2011 and 28,000 annual tour departures in 2017). 

AirScene is a proprietary software package developed and licensed by Rannoch Corporation that provides data 

to the CCDOA regarding aircraft and helicopter operations at McCarran. The CCDOA has used the software 

package since July 2000. 

Final EA for a Southern Nevada Regional Heliport D-7 December 2008 

Appendix D 

2 
Clark County Department of Aviation 

Table D-2 

Helicopter Air Tour Departures – Proposed Action 

Year 

McCarran 

International Airport 

Annual Grand 

Canyon Tour 

Departures 

Annual Las 

Vegas Strip 

Tour 

Departures 

Heliport Site 1/ 

Annual Grand 

Canyon Tour 

Departures 

Annual Las 

Vegas Strip 

Tour 

Departures 

Other Facility 2/ 

Annual Grand 

Canyon Tour 

Departures 

Annual Las 

Vegas Strip 

Tour 

Departures 

Total 

Annual Grand 

Canyon Tour 

Departures 

Annual Las 

Vegas Strip 

Tour 

Departures 

Historical 

2004 33,190 11,501 - - - - 33,190 11,501 

2005 37,595 12,775 - - - - 37,595 12,775 

2006 36,865 12,045 - - - - 36,865 12,045 

Forecast 

2011 9,800 8,500 29,500 - 4,400 6,700 43,700 15,200 

2012 10,200 8,600 30,700 - 4,500 7,200 45,400 15,800 

2013 10,600 8,700 31,900 - 4,700 7,700 47,200 16,400 

2014 11,000 8,800 33,200 - 4,900 8,300 49,100 17,100 

2015 11,500 8,900 34,500 - 5,100 8,900 51,100 17,800 

2016 11,900 9,000 35,900 - 5,300 9,500 53,100 18,500 

2017 12,400 9,100 37,300 - 5,500 10,100 55,200 19,200 

Notes:


1/ It was assumed that Las Vegas Strip tours would not be accommodated at the proposed Heliport site.


2/ Not evaluated in the environmental assessment. 


Sources: Clark County Department of Aviation using data from AirScene (2004 departures); Ricondo & Associates, Inc. 

Prepared by: Ricondo & Associates, Inc., April 2008 

Table D-3 

Helicopter Air Tour Departures – No Action Alternative 

McCarran International Airport Other Facility 1/ Total 

Annual Grand Annual Las Annual Grand Annual Las Annual Grand Annual Las 

Canyon Tour Vegas Strip Canyon Tour Vegas Strip Canyon Tour Vegas Strip 

Year Departures Tour Departures Departures Tour Departures Departures Tour Departures 

Historical 

2004 33,190 11,501 - - 33,190 11,501 

2005 37,595 12,775 - - 37,595 12,775 

2006 36,865 12,045 - - 36,865 12,045 

Forecast 

2011 29,500 8,500 14,200 6,700 43,700 15,200 

2012 30,600 8,600 14,800 7,200 45,400 15,800 

2013 31,900 8,700 15,300 7,700 47,200 16,400 

2014 33,100 8,800 16,000 8,300 49,100 17,100 

2015 34,500 8,900 16,600 8,900 51,100 17,800 

2016 35,800 9,000 17,300 9,500 53,100 18,500 

2017 37,300 9,100 17,900 10,100 55,200 19,200 

Note:


1/ Not evaluated in the environmental assessment. 


Sources: Clark County Department of Aviation using data from AirScene (2004 departures); Ricondo & Associates, Inc. 

Prepared by: Ricondo & Associates, Inc., April 2008 

Final EA for a Southern Nevada Regional Heliport D-8 December 2008 

Appendix D 
Clark County Department of Aviation 

Helicopter Fleet Mix 

The helicopter fleet mix consists of two helicopter types – the AS350 and the EC130. The 

percentages of departures by helicopter type and year are shown in Table D-4. These fleet mix 

percentages were applied to the operations data used in the INM analysis for the Proposed Action 

and No Action alternative. 

Table D-4 

Percentage of Departures by Helicopter Type 

Helicopter Type 

Year AS350 EC130 

2004 80.0% 20.0% 

2011 53.2% 46.8% 

2017 42.9% 57.1% 

Source: Ricondo & Associates, Inc., based on helicopter air tour operator surveys. 

Prepared by: Ricondo & Associates, Inc., April 2008 

Time of Day 

AirScene data were used to determine the number of helicopter operations at McCarran International 

Airport during the daytime hours (7:00 a.m. to 9:59 p.m.) and nighttime hours (10:00 p.m. to 

6:59 a.m.) in 2004. These data indicated that 1 percent of helicopter operations occurred during 

nighttime hours. As mentioned earlier, the calculation of DNL includes a 10-decibel weighting 

penalty for those operations occurring during the nighttime hours. It was assumed that the split 

between daytime and nighttime operations for each helicopter type would be the same in 2011 and 

2017 as that recorded in 2004. 

D.3.3.2 Heliport Operational Information 

The assumed future uses of the flight tracks to and from the airport or heliport are important in 

determining where helicopters are flying and, consequently, the noise levels generated on the ground. 

Helipad Use and Design Criteria 

Helipad use was determined based on several factors, including: historical wind analysis, 

conversations with helicopter operators at McCarran International Airport, air traffic control 

procedures in the vicinity of McCarran, Federal Aviation Regulations pertaining to helicopter 

operations, FAA Advisory Circulars pertaining to heliports and air traffic patterns, and observations 

of helicopter activities in the Las Vegas region. 

Specific criteria that were applied to the airspace analysis around the sites were referenced from FAA 

Advisory Circular 150/5390-2A, Heliport Design, 14 CFR Part 77 Objects Effecting Navigable 

Airspace, FAA Order 8260.42A Helicopter Global Positioning System (GPS) Non-Precision 

Approach Criteria, and data acquired from the Las Vegas TRACON and the FAA Digital 

Obstruction File. 

The wind analysis for the Heliport site utilized historical weather data from January 1992 to 

January 2001 collected at the McCarran International Airport weather station. Helipad use was 

calculated by assuming that helicopters would use helipads aligned with prevailing winds when 

Final EA for a Southern Nevada Regional Heliport D-9 December 2008 

Appendix D 
Clark County Department of Aviation 

winds are above three knots and would use the helipads providing the most direct route during calm 

winds. 

According to FAA criteria, the design of helicopter approach paths should be based on prevailing 

wind direction, crosswind component (150 degrees minimum), and clear approach and transitional 

surfaces at the heliport site. The Heliport Approach Surface for each landing area at a heliport is 

defined in 14 CFR Part 77 as the area beginning at the end of the take off and landing area with the 

same width, extending outward and upward for a horizontal distance of 4,000 feet, where its width is 

500 feet. The slope of the approach surface rises at a ratio of 8 to 1 eight feet horizontal to one foot 

vertical). The Heliport Transitional Surface is defined in 14 CFR Part 77 as that area that extends 

outwards and upward from the lateral boundaries of the heliport landing and takeoff area and from 

the Heliport Approach Surfaces for a distance of 250 feet from the centerline of the approach surface. 

The slope of this surface is 2 to 1. 

Design of the heliport landing areas was based on Visual Flight Rules (VFR) operations. However, 

intermediate and final missed approach design criteria as specified in FAA Order 8260.42A, 

Helicopter Global Positioning System Non Precision Approach Criteria, were considered in the 

design of the approach lighting area orientation in the event that an Instrument Flight Rules (IFR) 

approach is desired in the future. The optimum design for an instrument approach includes a 

three-mile intermediate segment, a 3-mile final approach segment, and a clear missed approach area. 

Planning data for the proposed Heliport is presented on Exhibit D-2. 

Generalized Aircraft Flight Tracks 

Flight track information is another important input to the INM. However, inputting the individual 

tracks for each aircraft operation is not practical and the FAA suggests that flight tracks be 

consolidated into a set of generalized flight tracks that are representative of all flight tracks into and 

out of the airport/heliport. Deviations from the generalized flight tracks occur because of weather 

conditions, pilot technique, air traffic control procedures, and aircraft weight. However, the 

generalized flight tracks do provide representative tracks for arrivals and departures at the 

airport/heliport. 

The potential flight corridors and the local routes for the Heliport site are shown on Exhibits D-3 

through D-5. The local routes represent generalized flight paths for transitioning between the site 

and the flight corridor. Each exhibit depicts the noise model inputs for each flight track scenario 

within the Proposed Action, including the flight corridors, the percentage of traffic on each corridor, 

and each local route. 

Exhibit D-3, Flight Corridors for Heliport site – Scenario A (Henderson), shows the Henderson 

departure flight corridor being used 100 percent of the time. Arrivals are split, with 80 percent 

arriving via the Henderson flight corridor and 20 percent arriving via the Charleston and Strip 

Railroad flight corridors. Exhibit D-4, Flight Corridors for Heliport Site – Scenario B (McCullough), 

shows the McCullough departure flight corridor being used 100 percent of the time. Arrivals are 

split, with 80 percent arriving via the McCullough flight corridor and 20 percent arriving via the 

Charleston and Strip Railroad flight corridors. Exhibit D-5, Flight Corridors for the Heliport site – 

Scenario C (Jean), shows the Jean flight corridor being used 100 percent of the time. Arrivals are 

split, with 80 percent arriving via the Jean flight corridor and 20 percent arriving via the Charleston 

and Strip Railroad flight corridors. 

Final EA for a Southern Nevada Regional Heliport D-10 December 2008 

Appendix D 

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Clark County Department of Aviation 

D.4 Ambient Noise Level Monitoring 

The ambient noise environment in the vicinity of McCarran International Airport and the Heliport 

site and in the vicinity of potential helicopter flight corridors associated with each site was evaluated 

through a noise-monitoring program. Continuous noise monitoring for a minimum of 24 hours was 

conducted at 10 locations3

 as shown on Exhibit III-5 in Chapter III. Two of the noise-monitoring 

sites represent alternative heliport sites, noted as McCarran International Airport and South of 

Sloan (Proposed Action), and eight of the noise monitoring sites are located underneath or near 

existing or potential helicopter flight corridors, noted as R1 through R8. Exhibits D-6 through D-15 

summarize the hourly Lmax, Leq, and L90 noise levels measured at each site, along with the measured 

DNL for the 24-hour noise-monitoring period. A photograph of each noise monitoring site and the 

noise monitoring equipment set up at each site is included with each exhibit. The exhibits 

demonstrate that noise levels vary during the day and night, with the lowest noise levels generally 

occurring during the late night and early morning hours. 

Ambient noise level measurements were recorded during July and October 2004. Noise monitoring 

equipment consisted of Larson-Davis Laboratories (LDL) Model 820 sound level analyzers equipped 

with Bruel & Kjaer (B&K) Type 4176 0.5-inch microphones. The instrumentation was calibrated 

prior to use with a B&K Type 4230 acoustic calibrator, and complies with applicable requirements of 

the American National Standards Institute (ANSI) for Type 1 (precision) sound level meters. 

The LDL Model 820 sound level analyzers run continuously with a sampling rate of 32 per second. 

The analyzers calculate various statistical descriptors of noise and DNLs for each 24-hour noise 

measurement period. As discussed previously, DNL is the average sound pressure level in 

A-weighted decibels for an average day of the year. DNL is calculated using the sound energy 

generated by individual aircraft operations (arrivals or departures), the number of operations 

occurring during a theoretical average 24-hour period, and the time of day the operations occur. A 

10-dB weighting penalty is added for aircraft or helicopter operations occurring between 10:00 p.m. 

and 6:59 a.m. 

In addition to the 10 sites noted above, ambient noise monitoring data from two locations beneath the 

Overflight Area, from an unrelated project conducted by the Federal Aviation Administration4

, was 

also evaluated. These two noise monitoring sites, noted as L05 and L07, are also shown on 

Exhibit II-5 in Chapter III. Exhibits D-16 through D-17 summarize the average hourly Leq and L90 

noise levels measured by the FAA at each site, along with the estimated DNL for the 

noise-monitoring period. DNL values were estimated based upon average hourly Leq data from the 

above-referenced FAA study since measured DNL values were not reported in that document. A 

photograph of FAA sites L05 and L07 and the noise monitoring equipment setup at each of those 

sites is included with the exhibits. The exhibits demonstrate that noise levels vary during the day and 

night, with the lowest noise levels generally occurring during the late night and early morning hours. 

3 	 Noise monitoring sites were selected by Brown-Buntin Associates, Inc. with input from the CCDOA and the 

Bureau of Land Management. 

4 	 FAA, Baseline Ambient Sound Levels in Lake Mead National Recreation Area (DOT-VNTSC-FAA-06-13, 

April 2006. 

Final EA for a Southern Nevada Regional Heliport D-15 December 2008 

Appendix D 
South of Sloan Site 

Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

July 01, 2004 

dB(A)

 Lmax

 Leq 

L(90) 

DNL=69.2 
McCarran International Airport 

Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

August 03, 2004 

dB(A)

Lmax

 Leq 

L(90) 

DNL=62.2 
Site R1 

Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

October 13, 2004 

dB(A)

 Lmax

 Leq 

L(90) 

DNL=50.6 
Site R2 

Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

October 13, 2004 

dB(A)

 Lmax

 Leq 

L(90) 

DNL=59.7 
Site R3 

Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

October 13, 2004 

dB(A)

 Lmax

 Leq 

L(90) 

DNL=55.1 
Site R4 

Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

October 28, 2004 

dB(A)

 Lmax

 Leq 

L(90) 

DNL=56.2 
Site R5

 Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

October 28, 2004 

dB(A)

 Lmax

 Leq 

L(90) 

DNL=50.2 
Site R6 

Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

October 28, 2004 

dB(A)

 Lmax

 Leq 

L(90) 

DNL=49.4 
Site R7 

Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

October 28, 2004 

dB(A)

 Lmax

 Leq 

L(90) 

DNL=46.8 
Site R8 

Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

Ocotber 28, 2004 

dB(A)

 Lmax

 Leq 

L(90) 

DNL=45.1 
Site L05 (LMNRA) 

Average Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

May 6- 22, 2004 

dB(A)

Leq 

L90 

DNL=41.8 
Site L07 (LMNRA) 

Average Hourly Noise Levels 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

0:002:004:006:008:00

10:0012:0014:0016:0018:0020:0022:00 

May 5-21, 2004 

dB(A)

Leq 

L90 

DNL=55.1 
Clark County Department of Aviation 

D.5 Noise Grid Analysis for Locations of Interest (LOIs) 

Cumulative noise exposure near existing and potential helicopter flight corridors was evaluated for 

the ten noise monitoring locations described in Section D.4, including FAA sites L05 and L07, and at 

seven supplemental locations representing noise-sensitive locations in the region, such as residential 

areas, schools, recreation areas, and potential animal habitats. These locations, referred to as grid 

points, are shown on Exhibit IV-5 in Chapter IV. Table D-5 indicates the land use or receptor 

represented by the grid points, and summarizes the ranges of predicted helicopter noise exposure for 

each grid point. These ranges in noise exposure were determined using the INM, and represent 

helicopter activity levels that would occur under the Proposed Action or No Action alternative. 

Helicopter noise levels are reported in terms of cumulative (DNL) and single-event (Lmax) exposure. 

The Lmax is considered a supplementary noise metric, and Lmax values are reported for informational 

purposes. 

Noise exposure underneath or near the existing and potential helicopter flight corridors is dependent 

partly on the altitude at which the helicopters would be flown. For the purposes of the noise analysis, 

the lowest altitude analyzed for helicopter flight corridors was 300 feet AGL. This is the minimum 

altitude above the ground required by 14 CFR Part 135, Operating Requirements: Commuter and On 

Demand Operations and Rules Governing Persons on Board Such Aircraft. 

According to the air tour operators, the minimum expected vertical distance between the helicopters 

and the terrain along the routes during Grand Canyon helicopter air tours would be 500 feet when 

feasible. This would be a voluntary action on the part of the air tour operators. 5 

Helicopter DNL values were calculated at the reference grid points using Version 7.0 of the INM. 

The calculation procedure consisted of using the INM to determine SEL values for individual 

overflights by the AS350 and EC130 helicopter types and then combining predicted SEL values with 

the forecast number of helicopter operations on the closest helicopter flight corridors to the grid 

points. Calculations were conducted for both the 2011 and 2017 helicopter activity levels. The DNL 

values reported in Table D-5 represent potential helicopter flight altitudes ranging from 300 to 

1500 feet AGL. Typically, for receptors located directly beneath a flight corridor, the highest DNL 

values would occur when the helicopters are at the lowest potential altitude. However, for receptors 

located farther away from flight corridors, the highest DNL values may occur when the helicopters 

are relatively higher above the ground. This occurs because absorption of noise by the ground 

(referred to as lateral attenuation) increases with distance from the helicopter flight corridor and as 

the angle of the helicopter above the ground becomes smaller with reference to the receptor location. 

5 14 CFR Part 135, Operating Requirements: Commuter and On Demand Operations and Rules Governing 

Persons on Board Such Aircraft, requires a minimum altitude of 300 feet AGL for helicopter operations when 

over congested areas; however, the Grand Canyon helicopter tour operators currently attempt to achieve a 

minimum altitude of 500 feet AGL. 

Final EA for a Southern Nevada Regional Heliport D-28 December 2008 

Appendix D 
Clark County Department of Aviation 

Table D-5 

Summary of Helicopter Noise Levels at Locations of Interest 

Nearest Helicopter Distance to Nearest Measured Ambient Predicted Helicopter Noise Levels Predicted Helicopter Noise Predicted Single Event Helicopter 

Grid Point 1/ Representative Land Use Flight Corridor(s) 2/ Flight Corridor(s) (feet) Noise Level (DNL) 3/ (DNL) No Action Alternative 7/ Levels (DNL) Proposed Action 7/ Noise Levels (Lmax) 4/ 

2011 2017 2011 2017 EC130 SA350D 

R1 Recreation area (trail) Charleston 0 50.6 44-53 45-55 39-49 40-50 61-78 65-80 

R2 Abandoned mine Tropicana 3,310 59.7 34-37 34-38 29-32 30-33 47-53 51-59 

R3 Undeveloped land Henderson (Inbound/Outbound) 7,600/2,340 55.1 n.a. n.a. 39-43 40-43 53-58 55-62 

R4 Undeveloped land Henderson (Inbound/Outbound) 21,580/16,330 56.2 n.a. n.a. <25 <25 <35 <35 

R5 Sloan Canyon petroglyphs McCullough (Inbound/Outbound) 8,110/13,520 50.2 n.a. n.a. 26-28 26-29 31-37 36-43 

R6 Wilderness area with hiking trails McCullough (Inbound/Outbound) 2,580/2,580 49.4 n.a. n.a. 40-43 40-44 51-56 54-60 

R7 Wilderness area with hiking trails Jean (Inbound/Outbound) 3,170/2,090 46.8 n.a. n.a. 42-44 42-44 55-59 57-63 

R8 Electric power substation Jean (Inbound/Outbound) 1,810/3,410 45.1 n.a. n.a. 42-43 43-45 46-52 51-57 

G1 Residential/school area Charleston 5,300 n.a. 27-33 28-34 22-28 22-28 39-45 44-51 

G2 Recreation area (campsite) Tropicana 1,430 n.a. 43-47 44-48 38-43 39-43 59-66 62-69 

G3 Residential area Henderson (Inbound/Outbound) 8,080/2,880 n.a. n.a. n.a. 36-40 36-40 49-55 52-59 

G4 Recreation area (trail) Henderson (Inbound/Outbound) 22,420/17,110 n.a. n.a. n.a. <25 <25 <35 <35 

G5 Wilderness/habitat area McCullough (Inbound/Outbound) 3,320/8,730 n.a. n.a. n.a. 33-37 33-37 47-53 51-57 

G6 Wilderness/habitat area Jean (Inbound/Outbound) 8,200/13,580 n.a. n.a. n.a. 26-28 26-29 31-37 36-43 

G7 Residential area Strip Railroad 0 n.a. n.a. n.a. 37-47 38-48 61-78 65-80 

L05 5/ Semi-primitive/natural McCullough/Jean (Outbound) 2,440 41.8 6/ n.a. n.a. 36-41 36-42 53-58 55-62 

L07 5/ High use Charleston 1,100 55.1 6/ 43-48 44-49 38-44 39-45 60-70 63-73 

Notes: 

n.a. = Not applicable 


DNL = Day-night average sound level, expressed in A-weighted decibels 


1/ Grid point locations are shown on Exhibit IV-5. Noise measurements were conducted at Sites R1 through R8 and Sites L05 and L07 in 2004. 


2/ Existing and potential helicopter flight corridors are shown on Exhibit IV-5. 


3/ Ambient noise level data are from Table III-2. Sites G1-G7 are supplemental grid point locations where noise levels were calculated using the INM. Ambient noise measurements were not conducted at those locations. 


4/ Predicted Lmax values are shown as a range for individual overflights by the SA350D and EC130 helicopter types at altitudes ranging from 300 feet to 1500 feet above the observer location (grid point). 


5/ FAA ambient noise monitoring site and data as described in Baseline Ambient Sound Levels in Lake Mead National Recreation Area (DOT-VNTSC-FAA-06-13), April 2006. 


6/ DNL values estimated from hourly Leq data measured by the FAA as referenced in Note 5 above. 


7/ Predicted DNL values are for potential helicopter flight altitudes ranging from 300 feet to 1500 feet above the observer location (grid point). 


Source: Brown-Buntin Associates, Inc. 


Prepared by: Ricondo & Associates, Inc., December 2008 


Final EA for a Southern Nevada Regional Heliport D-29 December 2008 

Appendix D 
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Clark County Department of Aviation 

Based on the INM grid point analysis, it is expected that the highest DNLs would occur at the grid 

points closest to the existing or potential helicopter flight corridors. The highest DNLs would occur 

at grid points R1 (recreation area/trail) and G7 (residential area). The lowest DNLs (less than 

25 dBA) would occur at grid points R4 (undeveloped land) and G4 (recreation area/trail). At all grid 

points, calculated helicopter DNLs are predicted to be below the FAA’s DNL 65 significance 

threshold. In addition, at Sites R1 through R8, and FAA Sites L05 and L07, predicted DNLs from 

helicopter operations alone under the Proposed Action for 2011 and 2017 are anticipated to be 

comparable to or less than existing DNL values as measured during ambient noise level monitoring 

at the same locations in 2004. Similarly, the highest helicopter Lmax noise levels would also occur at 

grid points R1 and R7 and the lowest helicopter Lmax noise levels would also occur at grid points R4 

and G4. 

D.6 Helicopter Single Event Noise Level Measurements 

Noise from individual helicopter overflights, coordinated directly with the pilot in command to 

ensure a valid “fly-by” noise event was captured, was measured at seven of the eight ambient noise 

monitoring locations discussed in Section D.4. These locations are the same as those used to 

document existing ambient noise levels from all sources affecting the proposed Heliport site, but the 

“fly-by” noise assessment focused on direct helicopter overflight noise levels. These individual (or 

“fly-by”) monitoring sites are shown on Exhibit IV-5. 

At sites near existing air tour routes (Sites R1 and R2), single event noise was measured during 

normal scheduled air tour operations. Single event noise was measured during pre-arranged test 

flights at Sites R4 through R8. (Single event noise was not measured at Site R3 because test flights 

could not be scheduled that would work within constraints imposed by ongoing fixed wing 

operations at Henderson Executive Airport. It is believed that single event noise levels at Site R3 are 

adequately represented by measurements at Sites R1, R2, and R4.) 

Table D-6 summarizes the results of the single event helicopter noise monitoring at Sites R1 through 

R8. The mean (average) and range of measured maximum noise (Lmax) and SELs for the observed 

helicopter flights are presented in the table. Table D-6 indicates that mean SELs for measured 

helicopter noise events ranged from approximately 57 to 85 dBA. and that mean Lmax values for 

measured helicopter noise events ranged from approximately 43 to 76 dBA The variability in 

measured noise levels was primarily caused by differences in the distance between helicopter flight 

routes and individual monitoring sites. The highest noise levels were recorded at Sites R6, R7, and 

R8, where helicopters consistently flew almost directly overhead during the test flights. The lowest 

noise levels were recorded at Site R5 (Sloan Canyon petroglyphs), where the closest potential 

helicopter flight corridor is more than a mile to the north. 

Final EA for a Southern Nevada Regional Heliport D-30 December 2008 

Appendix D 
90 

Clark County Department of Aviation 

Table D-6 

Summary of Measured Single Event Noise Levels of Helicopter Overflights 

Helicopter Number Lmax, (dBA) SEL (dBA) Azimuth 2/ 

Site 1/ Type Sampled Average (Range) Average (Range) (Degrees) 

R1 AS350 11 58.3 (53.2-65.3) 72.1 (65.3-76.3) 45-90 

AS350 16 67.2 (59.9-70.0) 77.3 (69.7-79.7) 60-90 

R2 

EC130 2 68.9 (68.0-69.8) 77.7 (77.5-77.8) 

AS350 5 69.3 (68.3-70.2) 79.6 (79.0-80.5) 45-60 

R4 

EC130 5 67.8 (66.3-68.3) 77.7 (76.7-78.3) 45-60 

AS350 5 48.5 (44.5-50.2) 59.4 (55.9-61.5) 30 R5 

EC130 5 46.9 (42.6-48.5) 56.9 (51.8-58.1) 30 

AS350 10 70.6 (67.9-73.6) 81.9 (79.0-84.4) 60-90 

R6 

EC130 5 67.3 (64.2-69.5) 77.1 (74.7-78.0) 75 

R7 AS350 5 74.9 (72.3-76.4) 85.1 (83.6-86.4) 90 

R8 AS350 6 70.2 (67.5-73.8) 81.7 (78.5-84.2) 60-75 

Notes: 

Lmax = The maximum A-weighted sound level (Lmax) is the loudest part of a noise event, measured in decibels. 

As an aircraft passes an observer overhead, the noise increases to a maximum level and then decreases. 

SEL = Sound exposure level (SEL) is a time-integrated measure, expressed in decibels, of the sound energy of a 

single noise event at a reference duration of one second. 

1/ Designations correspond to the monitoring site locations shown on Exhibit IV-5. 

2/ The azimuth is the angle between the aircraft flight path and the microphone at the point when the aircraft is 

closest to the microphone. An azimuth of 90 degrees means that the aircraft passed directly over the 

microphone. 

Source: Brown-Buntin Associates, Inc., January 2005 

Prepared by: Ricondo & Associates, Inc., December 2008 

D.7 	 Predicted Single Event Noise Levels Beneath or near Helicopter 

Flight Tracks 

Exhibits D-18 and D-19 depict SEL values predicted by Version 7.0 of the INM for the AS350 and 

the EC130 helicopter types, respectively, at a range of flight altitudes and lateral distances from the 

flight route. Exhibits D-20 and D-21 depict Lmax values predicted by Version 7.0 of the INM for the 

AS350 and the EC130 helicopter types, respectively. Based on the information shown on the 

exhibits, the AS350 helicopter registers approximately 0.2 dB higher than the EC130 helicopter when 

the helicopters are directly overhead. As lateral distance from the helicopter flight route increases, 

the difference between noise levels generated by the two helicopter types becomes more pronounced. 

On the left side of the helicopter, the EC130 is approximately 1.0 dB quieter than the AS350 at a 

lateral distance of 3000 feet from the flight route. On the right side of the helicopter, the EC130 is 

about 3.5 dB quieter than the AS350 at a lateral distance of 3000 feet from the flight route. 

Final EA for a Southern Nevada Regional Heliport D-31 December 2008 

Appendix D 




Clark County Department of Aviation 

As shown on Exhibit D-18, the highest predicted SEL for the AS350 helicopter (83.3 dBA) would 

occur when the helicopter is 300 feet AGL and at a location of zero feet horizontally from the center 

of the flight track. As shown on Exhibit D-19, the highest predicted SEL for the EC130 

helicopter (83.1dBA) would also occur when the helicopter is 300 feet AGL and at a location of zero 

feet horizontally from the center of the flight track. Predicted SEL values shown in Exhibits D-18 

and D-19 are comparable to SEL values measured during actual helicopter overflights as described in 

Table D-6. 

As shown on Exhibit D-20, the highest predicted Lmax for the AS350 helicopter (80.0 dBA) would 

occur when the helicopter is 300 feet AGL and at a location of zero feet horizontally from the center 

of the flight track. As shown on Exhibit D-21, the highest predicted Lmax for the EC130 

helicopter (78.0 dBA) would also occur when the helicopter is 300 feet AGL and at a location of zero 

feet horizontally from the center of the flight track. Predicted Lmax values shown in Exhibits D-20 

and D-21 are comparable to Lmax values measured during actual helicopter overflights as described in 

Table D-6. 

D.8 	 FAR Part 150 Noise Compatibility Study Update, McCarran 

International Airport 

Beginning in 2005 and throughout 2006, the Clark County Department of Aviation conducted an 

Update to the 14 CFR Part 150 Noise Compatibility Study for McCarran International Airport, 

located in Las Vegas, Nevada. Four Open Houses were held during the preparation of the 14 CFR 

Part 150 Study Update (August 2005, October 2005, May 2006, and September 2006). The public 

comment period for the 14 CFR Part 150 Study Update was from August 29, 2006 through October 

6, 2006; a formal Public Hearing was held on October 3, 2006. 

The 14 CFR Part 150 Study Update is comprised of three volumes. Volume 1: Noise Exposure Map 

Report contains noise exposure maps (NEMs) for 2004, 2011, and 2017 and associated 

documentation. The 2004, 2011, and 2017 noise exposure maps are included herein as 

Exhibits D-22 through D-24. The Noise Exposure Map Report was submitted to the FAA in 

December 2006 for review and acceptance. Volume 2: Noise Compatibility Program (NCP) Report, 

describes 13 noise abatement measures and nine noise mitigation measures proposed for McCarran. 

The NCP report was submitted to the FAA in March 2007. It is anticipated that the FAA will 

complete its review of the NCP report in 2008. Volume 3 of the 14 CFR Part 150 Study Update 

includes a compilation of public comments regarding the 14 CFR Part 150 Study Update and 

responses to those comments, and details the extensive outreach programs undertaken during the 

development of the 14 CFR Part 150 Study Update. Volume 3 was submitted to the FAA in 

December 2006. 

Pursuant to Section 107(a) & (b) [Title 49, United States Code, Section 47506] of the Airport Safety 

and Noise Abatement Act of 1979, as amended, on July 10, 2007, the FAA completed its evaluation 

of, and has formally accepted, the 2004 and 2011 NEMs included in the Noise Exposure Map Report. 

Final EA for a Southern Nevada Regional Heliport D-36 December 2008 

Appendix D 
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