What are aircraft noise requirements and how are they met?

Aircraft noise is regulated at certification and airport operations. Certification: ICAO Chapter 14 (strictest current), FAR Part 36, measured at approach, takeoff, and sideline points. Cumulative margin below limits earns noise credit. Noise sources: Jet exhaust (dominant at takeoff), Fan/compressor (approach), Airframe (landing gear, flaps, slats), and Auxiliary power unit. Reduction approaches: Engine - High bypass ratio (quieter exhaust), chevron nozzles, acoustic liners in nacelle; Airframe - Landing gear fairings, slat treatments, and continuous trailing edge. Design integration: Nacelle sizing for acoustic treatment, Approach procedure optimization (continuous descent), and Engine rating (derate for noise). Additional considerations: Community noise footprint, Airport noise restrictions (curfews, fees), and Property noise exposure forecasts. Noise testing: Flyover measurements, Phased array source identification. Noise improvements of 20-25 dB have been achieved over decades; further gains are increasingly difficult.