to confirm their predicted noise and aerodynamic performance characteristics.

Source noise control for the smaller business jet aircraft fleet presents a somewhat different problem. Eighty percent (80%) of the aircraft in this fleet are powered by turbojet or very low bypass turbofan engines (with noise characteristics similar to that of the turbojet) (7). The noise problem is primarily associated with the jet exhaust characteristics. The options available to reduce this noise are installation of exhaust suppressor kits with weight increase and some performance loss, or by re-engining the aircraft with moderate bypass ratio turbofan engines which may improve performance.

Both of these options are being tested and evaluated by the business jet aircraft manufacturers at this time with substantial indication that satisfactory noise reduction programs are technologically feasible for this category of aircraft (3).

Two of the previously identified proposed regulations have essentially the same objective, that is, retrofit of the currently typecertificated subsonic low bypass ratio turbofan powered aircraft. The earlier "straight retrofit” notice (ANPRM 70-44) merely discusses the need for noise reduction and emphasizes that current technology is available for a feasible retrofit program. The later notice (ANPRM 73-3) on fleet noise level (FNL) was published after consideration of comments received in response to the first notice and presents a detailed methodology and implementation procedure that permits and encourages other alternatives as well as retrofit. The FNL proposal is well developed and could be converted to a regulation in a short time, while the straight retrofit proposal might require considerable additional development before it could be structured as a regulation.

The concept and structure of the FNL proposal is adequate to effectively exploit the current technology (nacelle retrofit), to encourage the use of near future technology (refan retrofit) as it becomes operable, to provide incentives for the phaseout of aircraft not amenable to retrofit by the introduction of new quieter widebody aircraft, and to require full implementation of future technology as it becomes feasible (12). In addition, the FNL concept would periodically provide a great deal of useful information to the Government on air carrier fleet size, mix, and utilization. However, there are several features in the proposal that weaken its effectiveness and should be removed, and there are several that would add strength if included. They are:

• Omit exemption for airplanes engaged in foreign air commerce. • Omit exemption for airplanes engaged in overseas air com

merce.

• Omit expiration date of 1 July 1978 and continue the FNL concept indefinitely to permit the implementation of technological advancements (e.g., refan) as they become available. • Include airplanes engaged in intrastate air commerce.

• Include FNL requirements for sideline noise as well as takeoff and approach.

The FNL proposal (ANPRM 73-3) with the above exceptions could be prescribed as a regulation that would be an effective retrofit rule for the immediate noise problem and also be an effective rule for insuring that future technology is adequately exploited. A fleet noise level rule would be superior to and obviate the need for a straight retrofit rule such as considered in ANPRM 70-44. Differences in opinion exist on most of the above subjects, as reflected in the EPA Aircraft/Airport Noise Study master file documents and task group reports.

A primary question, not addressed by the Agency in any of its Task Group's studies because of its policy rather than technical nature, is that of the degree of implementation of the Administrator's responsibilities for coordination of aviation noise research under the responsibilities and authorities established for the Administrator in Section 4 (c) of the Act. Following the recommendations of the Office of Science and Technology (OST) “Jet Aircraft Noise Panel" discussed in the Introduction of this present report, an "Inter-Agency Aircraft Noise Abatement Program" has been conducted under the combined overview and coordination within the Executive Branch of the Office of Science and Technology, the Office of Management and Budget, and the National Aeronautics and Space Council. This latter entity has perhaps had the most direct influence in the coordination of R&D efforts of NASA and of the Department of Transportation and FAA. It also has undertaken in its latter existence, recommendations relating to the application of military technology to civilian aviation use.

The Administrator recognizes that with the abolition of the Office of Science and Technology, and the National Aeronautics and Space Council, his coordinating role established in the Noise Control Act will have vastly important implications regarding major decisions yet to be made as to the degree and allocation of investments of Federal funds in apparently competing, but in fact perhaps compatible (if dealt with in a comprehensive time sequence), programs

for retrofit and development of new and quieter air transport systems. Because of the magnitude of the questions involved, and the evolving situation with regard to the assumption by the National Science Foundation of some of the advisory functions formerly conducted by OST, additional time is needed by the Agency to develop a complete protocol as to how these important responsibilities will be undertaken. In the interim, communications have been established among the responsible level officials of DOT, FAA, NASA and EPA, to provide for continuing necessary exchanges of information and, as appropriate, action by EPA. These informal arrangements will be translated into an effective formalized procedure before the end of FY 1974. They will be reported to the Congress in a periodic report on Federal activities as called for by Section 4 (c) (3) of the Act.

REFERENCES

1. Aviation Advisory Commission Report, Advance Copy, January 1973. 2. Aircraft/Airport Noise Study; Task Group 2 Report, "Operations Analysis Including Monitoring, Enforcement, Safety and Costs." July 1973. Section 2, Flight and Operational Noise Controls. (NTID 73.3). 3. Aircraft/Airport Noise Study, Task Group 4 Report, "Noise Source Abatement Technology and Cost Analysis Including Retrofitting," July 1973, Section 2, Current Technology Options. (NTID 73.5).

4. Aircraft/Airport Noise Study, Task Group 4 Report, "Noise Source Abatement Technology and Cost Analysis Including Retrofitting," July 1973. Section 3, Future Technology Options and Restraints. (NTID 73.5).

5. Aircraft/Airport Noise Study, Task Group 4 Report, "Noise Source Abatement Technology and Cost Analysis Including Retrofitting," July 1973. Section 6, Research and Development Recommendations. (NTID 73.5).

6. Noise Standards: Aircraft Type Certification-Federal Aviation Regulation Part 36.

7. Aircraft/Airport Noise Study, Task Group 4 Report, "Noise Source Abatement Technology and Cost Analysis Including Retrofitting,” July 1973. Section 1, Aircraft Fleet Size Forecasts. (NTID 73.5). 8. Aircraft/Airport Noise Study, Task Group 4 Report, "Noise Source Abatement Technology and Cost Analysis Including Retrofitting," July 1973. Section 1, Technology Evolution and Development. (NTID 73.5).

9. Aircraft/Airport Noise Study, Task Group 5 Report, "Review and Analysis of Present and Planned FAA Noise Regulatory Actions and Their Consequences Regarding Aircraft and Airport Operations." July 1973. Section 3, Review of FAA Regulatory Status. (NTID 73.6). 10. Aircraft/Airport Noise Study, Task Group 5 Report, "Review and Analysis of Present and Planned FAA Noise Regulatory Actions and Their Consequences Regarding Aircraft and Airport Operations." July 1973. Section 1, Legislative Evolution and Development. (NTID 73.6).

11. Aircraft/Airport Noise Study, Task Group 4 Report, "Noise Source Abatement Technology and Cost Analysis Including Retrofitting,” July 1973. Section 4, Cost and Economic Analysis. (NTID 73.5). 12. Aircraft/Airport Noise Study, Task Group 5 Report, "Review and Analysis of Present and Planned FAA Noise Regulatory Actions and Their Consequences Regarding Aircraft and Airport Operations," July 1973. Section 6, Recommendations. (NTID 73.6).

SECTION 3

IMPLICATIONS OF IDENTIFYING AND ACHIEVING LEVELS OF CUMULATIVE NOISE EXPOSURE AROUND AIRPORTS

Measure of Environmental Noise Exposure

Section 7 (a) of the Noise Control Act of 1972 directs the Environmental Protection Agency to study the ". . . implications of identifying and achieving levels of cumulative noise exposure around airports." This section discusses selection of a method of measurement of cumulative noise exposure appropriate to public health and welfare effects, and considers the principal legal and economic implications resulting from its use.

These implications are discussed in terms of the day-night average sound level adopted for this report as the measure of cumulative noise exposure. However, the implications are insensitive to minor variations in the definition of the measure selected, and would be essentially unchanged if discussed in terms of other possible measures of cumulative noise exposure.

Measure of Cumulative Noise Exposure

A physical measure of cumulative noise exposure applicable to evaluation of airport noise should be based on consideration of the following requirements:

1. The measure should correlate with the human responses regarding hearing loss, speech interference, and annoyance due to noise exposure.

2. The measure should be capable of assessing the accumulated effect of all noises over a specified time period.

3. The measure should be simple enough that it can be obtained by direct measurement without extensive instrumentation or elaborate analysis equipment.

4. The required measurement equipment, with standardized characteristics, should be commercially available.

5. The measure for airport noise should be closely related to measures currently used for noise from other sources.

6. The single measure of noise at a given location should be predictable, within an acceptable tolerance, from knowledge of the physical events producing the noise.

Every scientific investigation of airport/community noise, regardless of the country of origin, shows that the impact of aircraft/ airport noise is a function not only of the noise intensity of a single event (i.e., each takeoff or landing), but also a function of its duration and the number of events occurring throughout the day and night* (1). This fact is recognized in the documents of the International Standards Organization, the International Civil Aviation Organization, and the Organization for Economic Cooperation and Development relating aircraft noise to community response (2, 3, 4).

A number of methodologies for combining the noise from individual events into measures of cumulative noise exposure have been developed in this country and in other developed nations, e.g., Noise Exposure Forecast, Composite Noise Rating, Community Noise Equivalent Level, Noise and Number Index, Noise Pollution Level. These methodologies, while differing in technical detail (primarily in the unit of measure for individual noise events), are conceptually very similar and are highly correlated with each other. Further, using any one of these methodologies, the relationships between cumulative noise and community annoyance (5, 6) are also highly correlated.

The day-night average sound level (Lan) adopted for use in the present EPA studies is consistent with existing methodologies and meets the previously stated requirements for a measure of cumulative noise exposure. It has been defined for this study as the average A weighted** sound level during a 24-hour time period with a 10dB penalty applied to nighttime (2200-0700 hours) sound levels.

The day-night average sound level especially excels, as a measure of cumulative noise among the several available measures, in that it can be easily measured with simple, relatively inexpensive equipment, and because it is appropriate to the wide variety of sources which create community noise environments. As has been shown in Reference 1, it can be used for interpreting cumulative noise exposure in terms of known health and welfare effects.

*Other factors have been considered in some studies to be relevant to particular effects, for example: attitude and prior experience with the intruding noise, residual or background noise, season (windows open or closed).

**The use of an A weighted sound level precludes the assessment of penalties for the existence of tones in the noise in the interest of simplifying the measure procedure. When appropriate, penalties for tones and other subjective attributes should be made in source regulations such as in FAR 36.