Noise measurements in the AS 350 helicopter under the specific operating conditions of SAR mission

Abstract

The AS 350 helicopter is a small and versatile helicopter used in many countries by private and public operators. In some countries the model is also often used for SAR missions. In the Brazilian public rescue services, AS 350 helicopters account for around 80 percent of the whole fleet. SAR missions often require operating conditions different from those for usual passenger transport. This includes flying and hovering with open doors or at low altitudes and low speeds. Noise exposure during SAR missions is of concern not only for the crew but also for the passengers, i.e. injured patients or newborn. While very important, data on acoustic conditions in SAR aircraft are scarce and do not exist for the AS 350 yet. Therefore, to investigate the noise in the AS 350 during SAR specific operating conditions different aircraft of the same model were equipped with recording equipment (microphone and SQuadriga II stand-alone front end ) and flown in the specific operating conditions of SAR missions. Recordings were analyzed using not only 1/n-octave and or FFT analysis, but also variable frequency resolution Fourier analysis for better low frequency analysis and psychoacoustic models available in ArtemiS Suite v12. Results show how noise characteristics vary depending on the operation of the aircraft, and which operating conditions are the most critical and should be avoided. The data can be used by SAR operators to build noise optimized mission profiles for critical missions, such as transportation of newborn and maintaining operational safety.