All subsonic jet and transport-category airplanes (those with an mtow of 12,500 pounds or more) for which application of a new type design is submitted on or after Jan. 1, 2006, will have to meet new noise certification levels, under a long-expected notice of proposed rule making (NPRM) published December 1.

The new levels, known as Stage 4, would be a cumulative 10 EPNdB (effective perceived noise level in decibels) less than the current Stage 3 limits. They are based on the work of the International Civil Aviation Organization’s committee on aviation environmental protection, in which the U.S. and the International Business Aviation Council are active members.

All business jets currently manufactured meet Stage 3 (by regulation) and virtually all could qualify to be recertified to meet Stage 4. Essentially, recertification potentially includes options such as re-analysis of existing noise certification and performance databases, weight and/or flap limitations and engine or airframe modifications. Therefore, depending on the aircraft model, recertification work could range from a mere formality of paperwork to a major modification. But the work required to bring older, out-of-production business aircraft into Stage 4 compliance is a far more complex challenge.

Although the proposal doesn’t contain a Stage 4 retrofit requirement and the FAA said it has no plans to impose such a requirement, one of the committee’s recommendations called for a phaseout by 2020 of Stage 3 airplanes with an mtow of more than 75,000 pounds. Stage 2 airplanes over that weight were last produced in 1988, but their operation was permitted for another 12 years. In its proposal, the FAA noted that 25 years elapsed between the adoption of Stage 3 in 1975 and an all-Stage 3 airliner and businessliner fleet in December 1999.

Despite the fact that a retrofit requirement has never been stipulated for business jets with an mtow less than 75,000 pounds, those that have not met the latest noise level standards have been singled out. For example, some local airport authorities, particularly in the U.S. and Europe, ban non-Stage 3 airplane operations altogether or, in some cases, at night. Operators of non-Stage 3 airplanes sometimes suffer from negative public relations even when they can prove their Stage 2 business jet is technically quieter than a Stage 3 heavy airliner.

After Stage 4 has been in effect for a while, it’s likely that operators of Stage 3 business jets will start getting treated the same way Stage 2 airplane operators are treated now. Further, those companies that worked so hard and long to develop hush kits to bring Gulfstream IIs and IIIs into compliance with Stage 3 might find themselves tasked to do it all over again to try and get these business jets into compliance with Stage 4–an improbable goal under the current level of technologies and materials.

This proposal is intended to provide uniform noise certification standards for Stage 4 airplanes certified in the U.S. and those airplanes that meet the new ICAO Annex 16 Chapter 4 noise standard.

The FAA believes that in 2006, when the proposed rule would become effective, all new type design subsonic jet airplanes and subsonic transport-category large airplanes will be able to meet the Stage 4 noise standard by using currently available noise-reduction technologies. Therefore, the proposed rule would impose “minimal, if any, cost” on manufacturers. However, to meet the proposed Stage 4 standard, “weight and engine constraints could be imposed on certain aircraft configurations.” Therefore, the FAA specifically requests comments from entities that could be negatively affected as a result of any weight and engine constraint and requests that all comments be accompanied by documentation.

All but one currently produced business aircraft models meet the proposed Stage 4 standards, said the FAA. That model, according to the agency, is the Raytheon Beechjet 400A (now the Hawker 400XP), whose original type certificate dates back to the Mitsubishi Diamond in 1981. Under this rule, the aircraft can continue to operate. What modification, if any, could bring the Hawker 400XP into compliance with Stage 4 was not immediately known. But in any case, the model is not required to meet Stage 4.

Commenter Wants Bizjet Stage 3 Retrofit
Of the few comments that had been submitted by press time, the most provocative came from Martin Gardner. Although his submission was not on company letterhead, he is director of engineering for Miami-based Quiet Technology Aerospace, one of three companies that has developed Stage 3 hush kits for Gulfstream IIs and IIIs.

Therefore, not surprisingly, Gardner believes the NPRM should be revised to require Stage 3 retrofits for business jets. All jets with an mtow of more than 75,000 pounds have already been Stage 3 compliant for four years. Gardner also believes the new Stage 4 rule should apply to all new jets, regardless of weight.

Excerpts from his comments:
“This emphasis on the heavier airliner, which typically operates from a major hub or other large airport, leaves residents who live adjacent to smaller, regional business airports unprotected from excessive noise levels generated by older-generation aircraft that fall below the 75,000-pound threshold weight.
“The business aviation community has been using the existing rules to continue to operate older business jets that are less than  75,000 pounds mtow and do not comply with Stage 3 noise limitations. Maybe there is a misconstrued notion that the lighter the aircraft the lower the noise level. That is not true. For a given aircraft group, Stage 2 or Stage 3, there is a general relationship between noise and weight. The greater the weight, the higher the noise limit is, and generally the noisier the aircraft.
“Under the regulations as currently written, and as the NPRM states, there continues to exist the opportunity for these noisy business aircraft to continue to operate at the expense of residents and workers.”

Gardner asked the FAA to revise the NPRM to “make Stage 3 and 4 noise levels applicable to all transport-category aircraft irrespective of mtow. Aircraft not complying with Stage 3 should be compliant by January 1, 2006. Aircraft for which a type design application is received on or after January 1, 2006, should comply with Stage 4.” Under the current NPRM, the latter is proposed only for all transport-category airplanes.

The FAA won’t respond to any other comments until after the comment submission deadline closes, when the agency will eventually publish either a revised NPRM, an interim rule or a final rule. Comments on the proposal are due by March 1. For more information, contact the FAA’s Laurette Fisher at (202) 267-3561.