The FAA has issued a notice of proposed rulemaking (NPRM) aimed at reducing noise generated by new helicopters and supplemental type certificate (STC) modifications for new helicopters certified under Part 36 (noise standards) of the federal aviation regulations (FARs).
The proposed rule would impose standards already adopted by the International Civil Aviation Organization (ICAO, Annex 16, Vol. 1, Chapters 8 & 11, Amendment 7). The new “Stage 3” standards would apply to all new helicopters in all phases of flight and be measured in effective perceived noise level in decibels (EPNdB) for helicopters weighing more than 3,125 pounds. The new noise standards are based on a logarithmic formula based on maximum weights of 176,370 pounds down to 3,125 pounds. (The maximum weight figure is high in relation to current helicopter technology. The Russian Mi-26, for example, is large by modern standards and has an mtow of about 123,000 pounds, and the Sikorsky CH-53E has an mtow of 73,500 pounds.) Helicopters weighing less than 3,125 pounds would have a maximum noise limit of 82 decibels SEL (sound exposure level/noise meter). The formula sets a noise ceiling for helicopters that weigh 176,370 pounds or more during takeoff, flyover and approach. For the maximum weight value that equates to EPNdBs of 106, 104 and 109, respectively for these flight phases. The noise formula decreases permissible noise at a rate of 3.01 EPNdB per halving of helicopter maximum weight to a floor of EPNdBs of 86, 84 and 89, respectively for helicopters weighing more than 3,125 pounds.
“The proposal of these more stringent noise certification standards into U.S. regulations is consistent with the FAA’s goal of harmonizing U.S. regulations with international standards,” wrote Lourdes Maurice, director of the FAA’s office of environment and energy. “Although ICAO adopted increased noise stringency standards for helicopters in 2002, the United States has yet to adopt these standards into Part 36. There has been heightened public awareness of helicopter noise in the United States, and the FAA has determined that the public would benefit from adoption of these more stringent standards.”
Decades of Noise-reduction Standards
The FAA’s attempt to regulate helicopter noise is decades old. It began in 1979, when the agency issued, and subsequently withdrew, an NPRM to mandate helicopter noise certification standards after being persuaded they were not feasible with technology at the time.
In 1982 the FAA, NASA and industry embarked on a $20 million joint research program aimed at developing noise-abatement technology and noise-prediction tools. Another noise-standard NPRM was issued in 1986 consistent with the technology of the time. In 1988 that NPRM was incorporated into Part 36 of the FARs governing noise emission standards for new helicopters. Those regulations designated Stage 1 helicopters as those that did not meet the new limits or had never been tested. Stage 2 helicopters met the new standards. Part 36 applied to both original and amended helicopter type certificates and prohibited changes in the type design that could increase noise beyond proscribed limits.
The FAA does not expect the new standards to have widespread immediate impact. “Given the complexity and expense in developing new helicopter models, the FAA estimates that applications for two new helicopter type designs will be submitted in the next 10-year period; this would mirror the development of helicopter type designs in the last decade,” said the agency.
Finally, new standards are not expected to change the way helicopter noise is tested and measured.