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普惠公司正在研制“技术部件”以抑制ＪＴ9Ｄ发动机的噪音 ,使之符合国际民航组织即将规定的 4级噪音条例。条例可能要求噪音等级在 8ｄＢ与 11ｄＢ之间 ,低于现在的 3级标准 ,未经处理的ＪＴ9Ｄ发动机达不到此标准。这些ＪＴ9Ｄ发动机是 70年代首批装在波音 74 7上的高函道比
Pratt & Whitney is developing “technical components” to dampen the noise of the JT9D engine to bring it into line with the forthcoming Noise No.4 class of regulations by ICAO. Regulations may require noise levels between 8dB and 11dB, below the current level 3 standard, untreated JT9D engine does not meet this standard. These JT9D engines were the first high-duty-ratio mounted on the Boeing 74 7 in the 1970s