An Assessment of High-Altitude Cruise Noise

A quantitative assessment is proposed for high-altitude cruise noise arising from commercial airplane operations. Measurements were taken for a number of flights at a rural location in Northern England with minimal background noise level. Noise data are available as 1/3 octave band levels and as global metrics: peak noise level, peak equivalent noise level. Peak noise levels are in the range of 55 to 57 dBA. Altitudes involved are between 28,000 and 38,000 feet at flight Mach numbers 0.7 to 0.85. For selected flights (Boeing B787-900 and Airbus A319-100) we show a comparison between measurements and simulations. The former data are dependent on long range propagation effects and local atmospheric conditions. Parametric analysis with air temperature and relative humidity are found to be are less important that winds. It is demonstrated that it is possible to predict noise peak levels, but difficult to match real-world flyover acoustic signals. Frequency analysis indicates noise peaks at low frequencies (125-160 Hz) that are simulated correctly, and relatively high frequencies (~3 kHz) which are not fully explained.