Siasconset Noise Test

This test was conducted with a Nantucket Airlines Cessna 402 aircraft using a General Radio Noise Meter set to measure A-weight single event noise levels in decibels. The test meter was located on Front Street in the Village of Sconset, overlooking Codfish Park and the shoreline. Weather was VFR with a wind from 120 degrees at 6 - 10 knots. Ambient background noise ranged from 42-52 decibels, predominantly influenced by waves on the beach below. Occasional voices and vehicular traffic could be heard.

This test was conducted to determine the differences in measured decibel levels emitted from a Cessna 402 at different operational power settings, altitudes and distances offshore. Additionally, four observers recorded their "annoyance levels" in reaction to noise volume and frequency for each run.

Results derived from this test show that altitudes, power settings and distances offshore can modify noise levels dramatically. Most noticeably, distances offshore made the greatest impact on measured noise levels. Since noise volumes double for each 10-decibel increase, it can be seen from the data below that aircraft flying at 1/2 mile offshore are twice as loud as aircraft flying 1 mile offshore. Noise levels double again when flying along the shoreline.

Of interest was the observation that at distances greater than 1 mile offshore, although audible to the human ear, measurable aircraft noise volumes became difficult to distinguish from ambient background levels. Observers, however, felt that the noise frequency continued to be annoying at distances up to 1.5 miles.

The data in the table below presents information in the order in which it was collected. Twenty-one (21) individual runs were conducted at various altitudes, power settings and distances offshore. Comparing Run 1 with Runs 3 or 4, for example, show the reduction in recorded Noise Levels (db's) that can be achieved at a distance of one (1) mile offshore. Generally, for any constant power setting and altitude, a ten (10) decibel reduction in recorded aircraft Noise Level can be achieved for each 1/2 mile increment from shore. Our current VFR Flight Track procedures have been established at a distance of one (1) nautical mile from shore.

In summary, the success of Nantucket's offshore flight tracts depends upon aircraft flying the correct distance offshore. Aircraft at 1 mile offshore generate one-fourth the volume of aircraft noise as an aircraft flying directly overhead. Nantucket Memorial Airport will continue to encourage all pilots to fly offshore flight tracks at the correct distance in order to mitigate noise concerns of shoreline residents.

DIRECTION SPEED WIND: 120 DEGREES 6-10 KNOTS			AMBIENT BACKGROUND NOISE LEVEL (db's): 42-52		C-402 AIRCRAFT: N88833 NANTUCKET AIRLINES
RUN	DISTANCE OUT (nm)	DME	ALTITUDE (msl)	POWER SETTINGS	NOISE LEVEL (db's)	COMMENTS
1	0	3.2	1000	CRUISE	72.2
2	.5	3.7	1000	CRUISE	58.0
3	1.0	4.3	1000	CRUISE	47.0
4	1.0	4.1	1000	CRUISE	49.0
5	1.5	4.7	1000	CRUISE	46.0
6	2.0	5.2	1000	CRUISE	NR	Talking in Background
7	2.0	5.4	1000	CLIMB	NR	Ambient Background Noise Level
8	1.5	4.9	1000	CLIMB	50.5
9	1.0	4.2	1000	CLIMB	55.8
10	.5	3.9	1000	CLIMB	59.5
11	0	3.2	1000	CLIMB	76.5
12	0	3.4	3000	CRUISE	57.5
13	.5	4.0	3000	CRUISE	55.0
14	1.0	4.2	3000	CRUISE	57.0	Uncontrolled Simultaneous Noise
15	1.5	4.7	3000	CRUISE	NR	Ambient Background Noise Level
16	2.0	5.1	3000	CRUISE	NR	Truck Noise in Background
17	2.0	-	3000	CLIMB	NR	Not Done
18	1.5	4.8	3000	CLIMB	NR	Ambient Background Noise Level
19	1.0	4.4	3000	CLIMB	52.0
20	.5	3.8	3000	CLIMB	58.5
21	0	3.4	3000	CLIMB	61.5

POWER SETTINGS: -CRUISE - 2300 RPM, 26" MANIFOLD PRESSURE, 160 KIAS
-CLIMB - 2450 RPM, 29.5" MANIFOLD PRESSURE, 120-140 KIAS