Introduction Study Area Helicopters Methodology Results Conclusions Suggestions References Acknowledgements Appendix 1 Appendix 2 Appendix 3 Appendix 4 Appendix 5

Suggestions for Further Study Not recommended for further study. Professional experience indicates that the individual difference between helicopters of the same type and/or model is not enough to warrant the time and expense of taking additional sound measurements of other Vertol 107s and Kmax’s. Also, taking additional sound measurements in different forest types at log landings is not likely to produce significantly different results. The different adsorption of sound by different forest vegetation types is not likely to be worth the time and expense. (See more detailed discussion of sound attenuation resulting from vegetation in appendix 5.) Noise levels at hook points are not expected to be significantly different for the noise levels generated at the log landings for reasons discussed in appendix 4. Recommended for further study. Since different types and/or models of helicopters are known to have different acoustical properties, we recommend taking measurements of other types of helicopters that are typically used in helicopter yarding to further quantify the expected distance to the 92 dBA contour. Additional sound measurements taken of one or two more different types of helicopters during yarding would help support the assumption made in this report that the distance to the 92 dBA level contour around helicopters during yarding activities is likely to be only a few hundred feet and not thousands of feet.