UBLIC HEARING: Director of Development ... - City of Glendale

Arup Acoustics
Ms. Ricarda Bennett
May 15, 1996
Page 5
employed by DreamWorks operation has not been determined, thus the noise calculation of
future heliport operations is based on the Sikorsky S76 helicopter. A common helicopter for
passenger transportation, a Sikorsky S76, is used for calculation purposes. According to FAA
tests (ibid.), in general the twin turbine S76 generates about 3 dBA (SEL) 2 higher noise level
than the single turbine Bell 206L helicopter. The CNEL results for a possible day of helicopter
flights is illustrated in Table 5 where there are 4 daytime trips and 1 evening trip for a total of 10
landings and takeoffs.
Table 5 - Future Flight Operation and Estimated CNEL Values (possible operation scenario)
Based on Sikorsky S76 Helicopter
Number of Flight-Events per Day Estimated CNEL at
(oer Time Cateaories Neic hborhood Locations
0700-1900 I 1900-2200 I 2200-0700 Total Per Day 1 2 I 3 I 4
8 I 2 I 0 10 33 29 I 35 I 24
CONCLUSIONS
A comparison of the estimated CNEL values of the previous and proposed flight operations is
presented in Table 6 for neighborhood locations 1, 2, 3 and 4. As can be seen, the flight
operations proposed by DreamWorKs produces, on average, noise levels 23dB-28dB lower than
previous use of the heliport, as shown by the values given in the last row of Table 6.
Table 6 - Difference in CNEL Values Between Historical and
Proposed DreamWorks Flight Operations
Neighborhood Difference in CNEL
Locations (Previous Operations - Proposed Operations)
1974-1977 1978-1983 1978-1988 1989-1992
1 21 24 26 24
2 22 24 28 26
3 24 27 24 22
4 25 28 31 29
Averaae 23 25 28 25
The noise impact from the historical and proposed helicopter flight operations on the existing
sound environment is shown in Table 7. As illustrated by CNEL values in Table 7, the proposed
DreamWorKs helicopter flight operations would not increase the current overall sound
environment (CNEL (24-hrs)) of the neighborhood residential communities. The results of noise
calculations further indicate that the previous use of heliport could have increased the current
CNEL level by less than 1 dB. In contrast, the DreamWorks projected helicopter operation will
have no measurable impact on the current CNEL sound environment.
2 SEL = Sound Exposure Level
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