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P. Liu
Fig. 7.128 The albatross landing state (landing gear puts down)
the airplane flies over the observer’s head, the pitch of the noise changes.
In addition, the pure tone component or narrowband component of the
aircraft noise and the duration of flying over the observer’s head affect the
degree of annoyance that people feel about the aircraft noise. Therefore, the
effective perceived noise is proposed for the evaluation of aircraft noise. The
calculation and measurement of the effective perceived noise level is very
complicated, and can generally be estimated by adding 15 dB to the sound
level. NASA proposed in 1997 to reduce noise by 10EPNdB in 10 years
and 20EPNdB in 20 years. In addition, the noise level of civilian passenger
aircraft has gradually become an important indicator for airlines to consider
when purchasing aircraft. These are undoubtedly huge challenges for the large
civilian passenger aircraft that China is developing. The noise level is one of
the key factors for its ability to obtain airworthiness certificates and to occupy
a place in the world aviation field in the future.