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HomeMy WebLinkAbout1986-03-18-HFA-rpt 1- f• ; 1985 NOISE EXPOSURE LEVELS AT L.G. HANSCOM FIELD FEBRUARY 1986 REPORT NO. 250370 SUBMITTED TO: Ms. Joyce Hals Director, Planning and Statistics Massachusetts Port Authority L G Hanscom Field Bedford, MA 01730 SUBMITTED BY: Harris Miller Miller & Hanson Inc. 429 Marrett Road Lexington, MA. 02173 HARRIS MILLER MILLER & HANSON INC. Page ii TABLE OF CONTENTS Page LIST OF TABLES . . . . . . . . . . iii LIST OF FIGURES . • • 400 • 1 • 0 0 . . . iii 1. INTRODUCTION . . 1 2 1985 OPERATIONS AND CORRESPONDING NOISE EXPOSURE LEVELS 2 2 1 1985 Operations . . . . 2 2.2 Noise Exposure Levels . . 5 2 3 Trends in Operations and Noise Exposure 12 3 SUMMARY . . . . 00 17 - -4 HARRIS MILLER MILLER & HANSON INC. Page iii LIST OF TABLES Page TABLE 2.1 AVERAGE DAILY DEPARTURES . 3 TABLE 2 2 MONTHLY VARIATIONS IN AVERAGE DAILY NOISE EXPOSURE (EXP) FOR 1985 OPERATIONS . . • 8 TABLE 2.3 EXP VALUES FOR STUDY YEARS FROM 1978 THROUGH 1985 . 9 TABLE 2 4 MONTHLY VARIATIONS IN AVERAGE DAILY NOISE EXPOSURE (EXP) FOR 1985 OPERATIONS, DISAGGREGARTED BY AIRCRAFT TYPE 11 LIST OF FIGURES FIGURE 2.1 MONTHLY VARIATIONS IN AVERAGE DAILY DEPARTURES BY AIRCRAFT LARGER THAN SINGLE ENGINE PROPS -- 1985 OPERATIONS . . . 4 FIGURE 2 2 AVERAGE DAILY DEPARTURES FOR 12 MONTH INTERVALS -- 1983 through 1985 . . • • • 0 . . 11 FIGURE 2.3 AVERAGE DAILY EXP FOR GENERAL AVIATION AIRCRAFT -- 1983 through 1985 . . . . . • • • • • • • • • 12 FIGURE 2.4 AVERAGE DAILY EXP FOR MILITARY AIRCRAFT -- 1983 through 1985 . 13 FIGURE 2 5 AVERAGE DAILY EXP FOR ALL AIRCRAFT -- 1983 through 1985 . . . . . . . 14 FIGURE 2.6 AVERAGE DAILY EXP FOR ALL AIRCRAFT -- 1983 through 1985 . • • • • • • 15 - HARRIS MILLER MILLER & HANSON INC Page 1 I 1 INTRODUCTION _ - This report summarizes the fifth in a series of ;annUal;updates sponsored by the Massachusetts Port Authority designed to evaluate changes in operations and noise exposure levels at L G Hanscom Field The first of these projects was conducted in early 1982 and focused on the changes in noise exposure levels that had occurred between 1978 and 1981 The study was particularly concerned with whether any improvements in noise exposure could be attributed to noise rules adopted by Massport during the intervening summer of 1980. Operations data collected during the summers of 1978 and 1981 were used to predict noise exposure contours, the results suggesting that Day-Night Average Sound Levels (Ldn) had decreased on the order of 1 5 decibels (dB) despite an increase in traffic. The improvement occured as a result of a higher than average percentage of operations by aircraft meeting Federal Aviation Regulation (FAR) Part 36 noise limits. The report attributed this, in part, to Article II of Hanscom's noise rules which requires local compliance with FAR Part 36 noise limits, even if an aircraft is not required by the Federal regulation to meet those limits In addition to the development of noise exposure contours depicting these operational scenarios, the initial study also defined a screening procedure designed to evaluate future changes in the mix of operations without resorting to complex and costly noise exposure contours for each application. The metric, EXP, provides an indication of the total noise from a set of operations at an airport Changes in the metric reflect corresponding changes in Ldn Although EXP has been enhanced since its initial development, comparisons between the original screening procedure and actual contour values showed very good agreement and have led to the continued use of EXP in subsequent annual updates The second of the three projects involved a review of 1982 operations and their effects on noise exposure The actual sample data suggested the possibility of a further improvement in levels (less than 1/2 dB) compared to 1981 but raised questions regarding the validity of the comparison, given possible seasonal differences between data sampling periods Because of these uncertainties, considerable interest was directed toward Massport's computerized data base of operations scheduled for implementation at the end of 1982 The third and fourth evaluations in the ongoing analysis focused on 1983 and 1984 exposure levels using the fully implemented data base management system. This report is the fifth in the series, and it involves the evaluation and analysis of 1985 exposure levels. Individual operations by aircraft larger than single engine piston props have been logged throughout the year by aircraft registration number, aircraft type, time and type of operation, and the aircraft owner/operator. Data are accumulated daily and sorted monthly for use in estimating resultant noise exposure levels HARRIS MILLER MILLER & HANSON INC. Page 2 ' u 2. 1985 OPERATIONS AND CORRESPONDING NOISE EXPOSURE LEVELS Massport's data management system utilizes a 15et of files ofaircraft operations data to summarize activity levels, to identify aircraft operations subject to surcharge, and to compute estimates of resulting noise exposure. Input to these files comes from several sources: (1) FAA flight strips used to record IFR (Instrument Flight Rules or instrument directed) departures, (2) monthly operations reports submitted to Massport from based operators, and (3) night surcharge logs maintained by Massport for operations between the hours of 11:00 p.m. and 7:00 a.m The only operations intentionally excluded from the data base are daytime single-engine propeller-driven aircraft These were shown in the original 1982 study to have only minor effects on the total noise environment down to about Ldn 55 Furthermore, if included in the noise calculations, the operations would demand an inordinate level of administrative support to achieve a minimal improvement in the noise predictions Thus, the only single-engine props recorded in the data base management system are those occurring during the night surcharge period which are traced in order to check compliance with Article IV of Massport's noise rules The estimation of noise exposure resulting from the data base fleet is then accomplished by assigning aircraft to one of 15 groups, each group characterized by a similarity of size, number and type of engines, climb performance, and, ultimately, the noise of aircraft within the group. The individual noise level (actually the Sound Exposure Level, or SEL) of each group is then "weighted" for the number of operations by all aircraft in the group and summed over the entire fleet to obtain a single number estimate of exposure Changes in this single number estimate (EXP) for different mixes of aircraft approximate the magnitude of change in Ldn without requiring complex and costly processing of contours. A more detailed explanation of EXP follows in Section 2.2. 2.1 1985 Operations A summary of the average daily departures maintained in the data base for 1985 is shown in Table 2.1. Operations have been sorted by day and night hours for both general aviation (civil) and military aircraft, and are listed month-by-month to show the seasonal variation in activity Data for the month of July are excluded from the table because (1) the number of departures was approximately ten times higher than that for any other month, contrary to all other indications of activity, (2) no comparable increase showed up in FAA tower counts, and (3) the original flight strips and backup data normally used to develop the fleet mix were not saved, thereby making it impossible to confirm the reasonableness of the data for the month. Note from the operations data in Table 2 1 that approximately 95% of the traffic in multi-engine aircraft is attributable to general aviation operations. Only 2 to 3 departures per day can be attributed to military activity Busy months include March and August with departures averaging about 47 per day. Less busy months include January, February, October, and December with departures dropping to about 38 per day. Nighttime departures are generally less than once per night. HARRIS MILLER MILLER & HANSON INC. Page 3 TABLE 2.1 AVERAGE DAILY DEPARTURES Civil Military Civil & Military Month Day Night Total Day Night Total Day Night Total Jan 36.32 0 87 37 19 1.16 1 16 37 48 0.87 38 35 Feb 35.39 1 00 36 39 1.04 0.04 1 07 36 43 1 04 37 46 Mar 44 35 1 10 45 45 2.13 0 10 2.23 46 48 1 19 47 68 Apr 38.03 0.90 38.93 2.07 0.07 2.13 40 10 0 97 41 07 May 40 87 0 81 41 68 2.00 0.06 2 06 42 87 0 87 43 74 Jun 36.83 0.60 37.43 3 27 0.07 3 33 40 10 0 67 40 77 Jul Aug 42 65 0.68 43 32 2.58 0.03 2 61 45 23 0.71 45 94 Sep 39.33 0.47 39.80 2 60 2 60 41.93 0.47 42 40 Oct 36 26 0 23 36.48 2.58 0.03 2 61 38.84 0 26 39.10 Nov 39 00 0 57 39 57 2.87 2.87 41.87 0 57 42 43 Dec 36 10 0 81 36.90 2.10 0 03 2 13 38 19 0 84 39 03 1985 38 68 0 73 39 41 2 22 0.04 2 26 40 90 0 77 41 67 Comparing these figures to similar data for 1984 ("1984 NOISE EXPOSURE LEVELS AT L.G. HANSCOM FIELD", page 9; June, 1985), it is further noted that general aviation activity in multi-engine aircraft appears to be down slightly from earlier periods, generally consistent with national trends On the other hand, military operations logged in Massport's data base have increased over the past year, from about 1 1 departures per day in 1984 to 2.3 per day in 1985. Busy months in 1984 included May and August with 46 departures per day, generally comparable to the busy months of 1985 Less busy periods included winter months of January, March, November, and December averaging about 41 departures per day, slightly higher than the less busy months of 1985. The overall decline in activity from 1984 to 1985 is on the order of 2 departures per day. To help visualize the variations in data base operations for 1985, Figure 2.1 shows a plot of average daily departures for each month of 1985 (except July), for civil and military aircraft separately Military activity, in particular, appears relatively stable, generally fluctuating between 2 and 3 depatures per day throughout the year. General aviation departures in large aircraft vary from a low of about 36 per day to as many as 45 per day over the course of the year. Peaks in general aviation activity occurred in March and August of 1985. These operations data are further disaggregated by aircraft type in later discussions of noise exposure which follow in the next section HARRIS MILLER MILLER & HANSON INC. Page-4 FIGURE 2.1 MONTHLY VARIATIONS IN AVERAGE DAILY DEPARTURES BY AIRCRAFT LARGER THAN SINGLE ENGINE PROPS -- 1985 OPERATIONS Average Daily Departures (Aircraft larger than 1 —eng piston) 50 45 - 40 - a 35 - a 0 30 - a 0 25 - 13 al 15 - 10 - 5 - 4 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month (1985) 0 Civil + Military o All HARRIS MILLER MILLER & HANSON INC. Page 5 2.2 Noise Exposure Levels 17 As background to the discussion of noise exposure levels comput44 for , ) Hanscom's aircraft operations, the following introductory paragraphs are reproduced from last year's report and are included to provide an overview of the manner in which noise has been tracked at Hanscom Field over the past several years. Noise in the vicinity of an airport is normally described using a measure of cumulative exposure that accounts for the loudness of each aircraft operation, the duration of each operation and whether it occurs during daytime or night hours in the course of a typical 24 hour period The measure used most frequently to characterize this exposure is referred to as the Day-Night Average Sound Level, or Ldn It was originally identified by the U S. Environmental Protection Agency as most appropriate for evaluating airport noise as well as other environmental noise sources based on the following considerations 1. The measure should be applicable to the evaluation of pervasive long-term noise in various defined areas and under various conditions over long periods of time 2 The measure should correlate well with known effects of the noise environment on the individual and the public 3. The measure should be simple, practical and accurate In principle, it should be useful for planning as well as for enforcement or monitoring purposes 4. The required measurement equipment, with standard characteristics, should be commercially available 5. The measure should be closely related to existing methods currently in use. 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 7. The measure should lend itself to small, simple monitors which can be left unattended in public areas for long periods of time Day-Night Average Sound Levels are normally depicted around an airport using lines or contours that connect points of equal noise exposure in much the same way that a meteorologist uses contours on a weather map to indicate points exposed to the same temperature and barometric pressure. However, noise exposure, like temperature and pressure, changes from day to day depending on which runway is in use and which aircraft happen to operate that day. Thus, the Ldn calculation procedure usually includes an averaging of the airport's operations over a full year 'to obtain a stable representation of the noise environment, free of fluctuations in wind direction, weather, and aircraft operations. Those are the conditions normally represented in a set of noise contours. HARRIS MILLER MILLER & HANSON INC Page 6 Because of the complexity of the activity at any airport similar to Hanscom, development of Ldn contours is a very comprehensive process, , It requires detailed knowledge of the fleet of aircraft using the airpot, the types of engines on the aircraft, climb performance characteristics, information on the frequency of runway use and where the aircraft fly as they depart and approach the field. All of these factors affect the noise in the surrounding communities. The process is especially detailed and refined for Hanscom because of Massport's interest in evaluating the overall effectiveness of its noise rules in controlling Ldn. For example, specific records of individual aircraft operations by aircraft type are maintained on a daily basis throughout the year; also, particular attention has been given to accurately modelling takeoff weights and throttle and flap settings used by the most frequent operators to get good characteristic estimates of the noise of individual aircraft Any intensive updating of Ldn contours with this level of detail would thus provide a very accurate representation of the changing noise environment at Hanscom As an interim measure, however, Massport uses a screening procedure designed to substitute for a complete noise contour set, yet give a reasonable estimate of the expected change in Ldn resulting from minor fleet changes This is done because it would be very inefficient to evaluate frequent and small changes in flight activity with a complete set of Ldn contours The measure of exposure used in this screening process is referred to as EXP It may be thought of as an indication of the total noise, in decibels (dB), produced by the entire fleet of aircraft using Hanscom regardless of which community they might fly over. It is the sum, in decibels, of the noise of each individual aircraft taking off from Hanscom over a point that represents the airport's closest residential neighborhoods Like Ldn, EXP also weights night departures (those between 10:00 p m. and 7 00 a.m. ) as if they were ten decibels louder than comparable daytime takeoffs to account for their more intrusive nature. What is important in this screening process is, however, not the specific value of EXP but rather the change in EXP from one case to another This change is indicative of the expected change in Ldn A change in EXP of 1 5 dB would probably be viewed as significant and worthy of more detailed analysis using complete Ldn contours To illustrate the use of EXP with two overly simplified examples, suppose that Hanscom currently has 100 departures per day by aircraft, each one of which produces an individual noise level of 90.0 dB. The noise exposure from the sum of these events, using the EXP screening process, is 110 0 dB If, in the future, it is expected that an additional ten of these aircraft will be taking off each day, the new EXP value would be 110 4 dB, indicating an increase in noise exposure of 0 4 dB That is also the magnitude of the expected change in Ldn resulting from the new activity The increase would not be viewed as particularly significant HARRIS MILLER MILLER & HANSON INC - -Page 7 - 7 t i If, conversely, future daily operations are expected to include just one departure by a much louder aircraft which produces an individual noise level of, say 107 0 dB, then the new EXP value would be 111 8 dB, a 1,8, dB, increase over the current exposure. Again, this is indicative -of the expected change in Ldn and, in this case, does represent a significant increase As is evident from the examples above, even with its simplifying assumptions, EXP is still a complicated procedure. Full documentation of the process is presented in detail in earlier technical reports available from Massport The individual noise levels associated with each aircraft used in the EXP calculation are known as Sound Exposure Levels (SELs) Aircraft having similar SELs or similar engine types and flight characteristics (intimating a similarity in their noise) have been grouped together for ease in the calculation of EXP Other aircraft, for example infrequent charter operations, have been included in a single, though possibly less representative category, simply because they are so infrequent as to not have much influence on the overall noise environment Examples of these aircraft are occasional 737s The EXP values for 1985 are presented in Table 2 2, month-by-month along with a summary of the operations from Table 2 1 shown earlier For the most part, general aviation aircraft are the dominant noise source, reflected in the higher "partial" EXP values under the columns of data labelled "civil" For example, in January of 1985, the partial EXP attributable to general aviation aircraft was 109 2 This is a full 10 dB higher than the partial EXP attributable to all military aircraft that same month (99.2). When military and civil operations are added together, the combined exposure of all operations is 109.6, or 0.4 dB above civil operations by themselves. The contribution from military aircraft is essentially negligible. Note, however, that civil aircraft do not always dominate the noise environment In June, for example, the partial EXP for military aircraft was 114.2, 4.0 dB above the partial EXP for civil operations The two elements combine to produce the highest EXP value for any period during year (115.6). Note that the military component is due almost entirely to nighttime operations which produced a partial EXP of 112 8. This is particularly interesting considering the number of average daily departures for June is relatively low compared to other months The implication of these observations is that there must have been a very loud nighttime operation by a military aircraft during the month, causing that very high contribution to the total noise. Subsequent review of operations by aircraft type, shown later in Table 2.3, indicates a single nighttime departure by a C-5A during the month. The example illustrates the importance of reducing loud nighttime operations; just one departure can significantly degrade overall noise exposure. It is also interesting to note how nearly equal the contributions are from civil and from military operations over all of 1985. The partial EXP from civil aircraft for the entire period is 109.2 The partial EXP from military aircraft is 108.1, only 1.1 dB less than the general aviation HARRIS MILLER MILLER & HANSON INC. Page 8 TABLE 2.2 MONTHLY VARIATIONS IN AVERAGE DAILY NOISE EXPOSURE (EXP) FOR 1985 OPERATIONS 1985 DEPARTURES-HAPSCa1 FIELD Average Daily Departures Average Daily Noise Exposure Civil Military Civil Military Total Month Day Night Total Day Hight Total ; Day Night Total Day Night Total Day Night Total Jan 36.32 0.87 37 19 1.16 1,16 ; 107 105,2 109.2 99.2 99.2 107.6 105.2 109,6 Feb 35.39 1.00 36.39 1.04 0.04 1.07 i 107.2 104.7 109.1 96.6 86.8 97 107.5 104.8 109.4 Mar 44.35 1.10 45.45 2.13 0.10 2.23 ; 107.6 99 108.2 108.3 107 4 110.9 111.4 108.5 113.2 Apr 38.03 0.90 38.93 2.07 0.07 2.13 108.1 93.4 108.3 107.9 71.3 107.9 110 93.5 111.1 May 40.87 0.81 41.68 2.00 0.06 2.06 ; 108.3 102.6 109.3 107.3 94.2 107.5 110.8 103.2 111,5 Jun 36.83 0.60 37 43 3.27 0.07 3.33 1 108.2 105,8 110.2 108.5 112,8 114.2 111.4 113.6 115.6 Jul Aug 42.65 0.68 43.32 2.58 0.03 2.61 1 108.4 102.9 109.5 109.8 85.6 109.8 112.2 103 112.7 Sep 39.33 0.47 39.80 2.60 2.60 ; 107 1 90.4 107.2 101.3 101,3 108,1 90.4 108.2 Oct 36,26 0.23 36.48 2.58 0.03 2.61 ; 107 92 107.2 104 104 108.8 92 108.9 Nov 39.00 0.57 39.57 2.87 2.87 106.5 107,5 110 105.6 105.6 109.3 107.5 111.5 Deo 36.10 0.81 36.90 2.10 0.03 2.13 106.3 105 109.2 102,5 102,5 108.1 107.4 110.8 1985 38.68 0.73 39.41 2.22 0,04 2.26 ; 107.6 103.9 109.2 106.2 103,6 108.1 110 106.7 111 7 a, 0-3s - _ HARRIS MILLER MILLER & HANSON INC Page 9 component. In all previous study years, the civil and military components have never been closer than 3 4 dB The implication is that military operations have become a much more significant element of the noise exposure around Hanscom than they have at any time since 1978 The brief table below summarizes changes in EXP since the start of these assessments in 1978 Where necessary, EXP values for earlier years have been adjusted to account for a nighttime weighting on departures between 10:00 p m. and 7:00 a.m as well as the upgrading of aircraft groups to provide for new aircraft types The comparison suggests that overall noise exposure levels have increased over the last several years though are still below the value computed for 1978. The most recent increase is directly attributable to increased significance of military aircraft TABLE 2.3 EXP VALUES FOR STUDY YEARS FROM 1978 THROUGH 1985 Civil Military Total Year Component Component EXP 1978 110.4 dB 108.1 dB 112.4 dB 1981 108 9 105.2 110 5 1982 108.4 105 6 110 2 1983 109 5 106.1 111.1 1984 110 0 105.3 111.1 1985 109.2 108 1 111 7 Table 2 4 shows EXP values on a month by month basis for 1985, further broken down by aircraft type Examination of the table shows that the aircraft group with the greatest contribution to annual average EXP is group 4 -- the oldest and noisiest business jets in the fleet (Lear 24s, 25s, and BAC1-11s) Though this group has an average of only 0 4 departures per day, its operations-weighted SEL is 105.4 dB Similarly, the average number of C-5A departures is only 0.03, but its weighted SEL is 105.2 These two groups alone account for nearly half the noise energy with only one percent of the average daily operations by large aircraft 0 or) aC Hms4E- $ U ti S. ..;g:.1 E 1 -' d g e U C2.- 2 .,y ti _ 0 0 H ri V. 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Z3 i N Fl! :I ;2.', U U e wU U U u., v U w U ®o .. ` 4, m S! u 4o a CW '" V 3E HE Va a a u ..v ee r a s a 2Ga _ - 8 s® P. m V V M w .; ® 2 a e �3 w a u u o ® 241 ffiea_ i a V a U r a _ w V U a a U U a FU6 v _ e ati i..! e Na W a Cl oN u LIN . e as r. e Flo 4 u ..n w ® u U u ®so E a .. c ;; o u a e u i uk' - e g; o a e e .7.. ® u u s H ee a v o 0 0 0 0 _ N a 7.4 m w 27 7 7 ; 2 7; u _ -' i.-E. ... ,. w 2 V 2 0 2 `g. e, ww V a s 2 P U 2 V' N 0 W0 ., - a o o ., Y o ' o e ; 6 .i _ ..2.1': .. ® a v a a u u ; g ; Wv - 2 4_ _ ra o m m m '-:l U HARRIS MILLER MILLER & HANSON INC. Page 11 LU h :?‘ 1 7 ,9 t!,3 2 3 Trends in Operations and Noise Exposure F- ^ c' One of the difficulties in comparing data fronfrone yeae to the next has been that of drawing conclusions about how much the noise has really changed over time. Values rise and fall in response to factors which can not always be isolated or are not intuitively obvious some winter months have higher exposure than some summer months and vice versa; some exposure levels are highest when total operations are lowest; some aircraft groups are significant one year and not the next; and so on. To help define trends in noise exposure, an annual average of the EXP values over the most recent 12 months, rather than over a specific calendar year, has been calculated starting with January 1983. With a current 12 month average, it is possible to view a new annual average EXP each month and compare it to previous 12 month periods without the complication of individual month-to-month fluctuations. (Prior to January 1983, data were unavailable at this level of detail and cannot be included in this last analysis). The same approach is used first to see trends in operations Figure 2 2 depicts the average daily departures by large aircraft (both civil and military) for the most recent 12 month period, beginning with the period 1 January 1983 through 31 December 1983 The next point on the figure is for the period 1 February 1983 through 31 January 1984, and so on A least squares line through these 12 month periods indicates a slight decrease in average daily operations over the past three years However, while generally decreasing, the figure does show a sharp increase in operations in August, 1984, resulting from an unusually heavy traffic period during the summer of 1984. It is not until 6 to 7 months after that period that its effects on average daily traffic are significantly reduced. Figures 2 3 through 2.6 depict the same types of trend lines, but in this case for EXP Figure 2.3 shows the trend in average daily EXP values for civil aircraft by themselves. This shows very nicely, the decrease in exposure resulting from the changeover to quieter aircraft Figure 2 4 shows the trend in EXP attributable only to military aircraft It shows a rise in EXP consistent with the calendar year results presented earlier in Table 2.4. A review of military operations suggests this increase is due to increased operations by C-141s, C-5As, and occasional KC-135s. Figure 2.5 repeats the results of Figures 2 3 and 2 4 at a more compressed scale and also shows the trend in EXP for all operations combined The results in this final figure indicate a slight increase in total EXP since the start of the study period in January 1983 The increase is only on the order of a few tenths of a decibel and appears to be attributable to recent increases in military activity. HARRIS MILLER MILLER & HANSON INC. Page 12 ft r a FIGURE 2.2 AVERAGE DAILY DEPARTURES BY LARGE AIRCRAFT FOR I r- ' - 12 MONTH INTERVALS -- 1983 through 1985 Average Daily Departures (12 Month Interval Average) 46.5 0 46 - 45.5 - ffi 45 - - L- 44.5 - a a. 0 44 - DI 0 ° 43.5 - 0 , co 43 - 1_4 Lb- 1 I ) 0 < 42.5 - 0 0 000 42 - Do 41 .5 - 0 41 J84 M84 M84 J84 S84 N84 J85 M85 M85 J85 S85 N85 Interval Ending (Month) 0 Computed + Least Squares HARRIS MILLER MILLER & HANSON INC. Page 13 r) I. I I FIGURE 2.3 AVERAGE DAILY EXP FOR GENERAL AVIATION AIRCRAFT OVER 12 MONTH INTERVASLS -- 1983 through 1985 EXP by 12 MONTH INTERVAL Civil Departures 109 8 E 109 7 - 109.6 - la 109.5 - 0 109 4 - 109.3 - 0 . 0 1092 - 1091 - o w 109 - 0 108.9 - 108.8 - 0 108.7 - 108.6 - 0 108.5 Ii J84 M84 M84 J84 S84 N84 J85 M85 M85 J85 S85 N85 Interval Ending (Month) 0 Computed + Least Squares I ' I L HARRIS MILLER MILLER & HANSON INC Page 14 19E:5 1,:;‘r) 17 9 49 FIGURE 2.4 AVERAGE DAILY EXP FOR MILITARY AIRCRAFT OVER 12 MONTH INTERVALS -- 1983 through 1985 -' EXP by 12 MONTH INTERVAL Military Departures 108.5 13 108 - 0 107.5 - 107 - 106.5 - CD I I I 1 0 a: 106 -L i 1LLI I I I " 105.5 - 0 0 105 - 0 Do 1 04.5 - o 0 0 0 0 104 - 0 D 0 0 103.5 ‘184 M84 M84 J84 S84 N84 J85 M85 M85 J85 S85 N85 Interval Ending (Month) Computed + Least Squares HARRIS HARRIS MILLER MILLER & HANSON INC. Pg e ct5 t FIGURE 2.5 AVERAGE DAILY EXP FOR ALL AIRCRAFT t - OVER 12 MONTH INTERVALS -- 1983 through 19851 Fi EXP by 12 Mont -) Interval 112 0 0 1:1 111ffl di 6 E3 6 th 11 6 6 O 6 6 El 13 1:1 1 1 0 - 0 0 4:1> " 4 124 109 - L L 2 2 m 108 - x x-0 0: wx 107 - 106 v v v-7 . v---4---4R-4"—wx 7 V '7 7 X 105 - X x x x x x 104 - x x x 103 - 111111111111111i J84 M84 M84 J84 S84 N84 J85 M85 M85 J85 S85 N85 Interval Ending (Month) 0 All Departures o Civil x Military HARRIS MILLER MILLER & HANSON INC. Page 16 3. SUMMARY Results of this evaluation indicate the following trends and conclusions: (1) General aviation operations in multi-engine aircraft are showing a continued trend towards the use of quieter aircraft Operations have been increasing in aircraft such as the Citation and Lear 35s and 36s while decreasing in older, louder Lear 24s and 25s, G-2s, and BAC1-11s Despite a net increase of about 0 7 corporate jet operations per day from 1984 to 1985, general aviation's contribution to EXP continues to decline. Values of EXP computed for 12-month intervals beginning in January 1983 show a decrease in noise exposure attributable to general aviation aircraft that is on the order of 0.7 dB through December 1985. (2) Military activity in large jet aircraft including the C-141, C-5A, C-9, and T-43 has increased by nearly 110 operations over the past year The effect of the first two aircraft, alone, has been to create an increase in the EXP due to military operations of almost 10 dB, and C-141 and C-5A operations have increased total exposure from all other aircraft operations combined by more than 2 dB. Given this significant effect on Hanscom's noise environment, it is desirable to minimize these transport category operations whenever possible and to assure that no unnecessary flights take place during nighttime hours. (3) The increasing effect of military transport operations at Hanscom is presently balanced by the decrease in exposure resulting from the use of quieter general aviation aircraft. The cumulative effect of both activities has been a relatively negligible 0.2 to 0.3 dB increase in EXP since Massport's data base was established in January 1983. Exposure is likely to increase more significantly, however, if military activity continues to expand 0)