Correction Methods for Aircraft Noise Control Zone and Noise Contours Planning at Heliports of the Republic of China (Taiwan)

摘要

The results of noise contours planning and monitoring data at heliports of the Republic of China (Taiwan) are often doubted by the public because of the gap between the measured noise level and the real noise perceived by the public. Is it because that the helicopter flight paths adopted in the current model are different from the real ones? Or there are situations in which more than one helicopters taking off simultaneously or team flying being needed during flight training? Or the records of flight paths made by the control tower are not complete? All these factors may lead to the inaccuracy of follow-up dynamic flight data input by the Aircraft Noise Monitoring Center and influence the results of noise contours planning. In addition, the helicopter has particular flight characteristics, such as hovering flight, longer standby time, slower flying speed, and lower flying altitude. However, the current model cannot achieve the level of real simulation of each flight situation due to such factors as meteorological conditions, flight speed, altitude and thrust when the helicopter is taking off or landing or hovering in the air. These factors tend to make a difference to the real take-off and landing flight paths, as well as standard operating procedures. A minor difference in the air may cause a huge variation as much as several kilometers on the ground. Besides, the low-frequency noise character of the helicopter may cause a difference to noise distribution. Therefore, we hope to establish correction methods for aircraft noise control zone and noise contours planning at heliports of the Republic of China (Taiwan) through on-the-spot measurement of aircraft noise. In terms of objective measurement, the mean deviation of noise level between A-weighting and C-weighting is 10 dB(A). However, whether or not this value represents a good correction to fit with surrounding residents' actual perception on helicopter noise will need to be supplemented with social investigation. The 50-50 method is usually used to confirm the correction. The definition of noise correction is "the variation between the helicopter noise and reference noise when they cause the same level of annoyance". Since the break-even point of the helicopter noise is 62dB, to reach equivalence of noise annoyance, the reference noise level needs to be corrected with +8dB(A) (subjective investigation: Investigation of people's actual perception of annoyance; 8dB(A) correction). Therefore, the correction is recommended to be 8dB(A) in order to fit with the public opinions and quench public complaints by meeting with the public's psychological perception.