Criteria for Selection of Measurement Positions for Maximal Jet Aircraft Sideline Noise

Present FAA noise certification requirements for subsonic jet aircraft specify uniquely the measurement locations for takeoff and approach noise. A third set of measurements is required to determine the maximum noise produced on the ground to the side of the flight path. The regulation specifies only the offset distance from the runway, requiring the applicant to determine where, longitudinally, measurements should be taken and to demonstrate that a maximum value is obtained. Based on three separate test programs for turbojet powered business aircraft, we show that the maximum sideline noise will occur when the angle between the ground and the aircraft is approximately 10°. Further, when reported as effective perceived noise levels, the sideline noise varies extremely slowly with distance along the runway after this angle is achieved. With very coarse assumptions as to the aircraft noise directivity pattern, a sideline noise measurement location can be selected which will meet the FAA requirements. A design chart for measurement point selection, using aircraft performance estimates as input data, is provided.