Shock wave cannot travel any further upstream and the pressure progressively builds in that region; a high pressure shock wave rapidly forms. Shock waves are not conventional sound waves; a shock wave takes the form of a very sharp change in the gas properties. Shock waves in air are heard as a loud "crack" or "snap" noise. Over longer distances, a shock wave can change from a nonlinear wave into a linear wave, degenerating into a conventional sound wave as it heats the air and loses energy. The sound wave is heard as the familiar "thud" or "thump" of a sonic boom,
Aircraft noise in development, plus new procedures could reduce noise levels by 10 dB and noise footprints by 50%, but more advances are needed to preserve or expand heliports. Package delivery UAS will need to characterize their noise, establish limits and reduce their impact. General: Aircraft noise Aircraft noise is noise pollution produced by aircraft during the various phases of a flight. Sound production is divided into three categories: Health consequences include sleep disturbance, hearing impairment and heart disease, as well as workplace accidents caused by stress. Memory and recall can also be affected. Governments have enacted extensive controls that apply to