A test program was conducted to isolate and evaluate the individual noise sources of a light helicopter. To accomplish this, the helicopter was mounted on a special test rig, at a 6-foot skid height, in a simulated hover. The test rig contained by dynamometer for absorbing engine power and an exhaust silencing system for reducing engine noise. This test set-up allowed the various components of the helicopter to be run and listened to individually or in any combination. The sound pressure level was recorded at a point 200 feet from the helicopter as the component parameters were systematically varied. The tests were conducted in an open area, during the middle of the night, with no wind, and with all other known variables either eliminated or kept as constant as possible.