Modeling floatplane noise at Isle Royale National Park: Concessions service scenarios

Olstad, Tyra; Lignell, Brent; Joyce, Damon

doi:10.36967/2313431

This study arose from Isle Royale National Park’s (ISRO) Technical Assistance Request (TAR; #2482), which identified the need to evaluate the noise associated with concessionaire float plane flights to and from the island and between designated landing locations within the park. The National Park Service’s (NPS) Natural Sounds and Night Skies Division (NSNSD) used an internally-created sound mapping tool called the Attenuation Calculator to model noise levels under six different scenarios: existing conditions, using a Cessna 206 and up to two de Havilland DHC-2 Beaver floatplanes to fly route segments out of Michigan and Minnesota; having two of each aircraft fly routes simultaneously; requiring the intra-island flightpath to loop farther offshore; replacing the DHC-2 Beavers with a Cessna 208 turbo-prop; replacing the Cessna 206 with a Cessna 208; and removing all Cessna 206 flightpaths (including intra-island and out of Minnesota) and flying only DHC-2 Beavers. Results are reported in terms of time above key sound levels and time audible at five selected locations within the park, representing a range of acoustic conditions and expectations for quietude. Maps depict the modeled geographic extent of aircraft noise during different flight segments using different aircraft. Based on this analysis, the concessionaire floatplane transportation service has the potential to generate noise of moderate duration and intensity at locations across ISRO. Under all scenarios, it is likely that visitors or wildlife can detect the presence of aircraft, and noise may interfere with visitors’ expectations of natural quiet. Noise would be most consistently audible under Scenario 2 and least audible under Scenario 6. The difference between existing conditions and Scenario 3 is nearly imperceptible. In each of the scenarios, aircraft noise is audible for the greatest amount of time at locations near the floatplane landing areas. Implementing Scenario 6 could greatly decrease time audible at some backcountry campsites, compared to existing conditions. Park managers are cautioned that the Attenuation Calculator has several limitations and that the results are estimates, intended only to help inform management decisions.

Modeling floatplane noise at Isle Royale National Park: Concessions service scenarios

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