Author(s): Zellmann Christoph, Jäger David, Schlatter Felix
The sound characteristics of approaching aircraft often contain tonal components, which increase the annoyance of the population affected. Airflow deflectors, installed at the airframe of the worldwide frequently flying Airbus A320 family, are a simple retrofit solution to suppress two of those prominent tones generated at the Fuel Overpressure Protector Cavities. Besides reducing the annoyance, the solution promises significant impact on commonly used A-weighted metrics. The manufacturer predicts reductions of up to 9 dB at distances between 12 and 50 km from the runway threshold. The aircraft noise emission model recently developed at the authors' institution is based on measurements from 2013 and 2014 where no such airflow deflectors were installed. As the local main carrier in Switzerland introduced such retrofit in 2015 to all aircraft types, the airframe noise model needs to be updated and validated for approach procedures. For this purpose, measurements at distances between 13 and 53 km from the runway threshold were carried out and analysed. A comparison of the adjusted aircraft noise emission models against measurements revealed a good agreement of the sound exposure levels. Furthermore, it was found that the tone generation clearly depends on the aircraft Mach number. At approach speeds of 0.35 Mach, the predicted one-third octave bands that are affected by those tones showed level differences between 5 and 8 dB resulting in an increase of the A-weighted overall level of 2.1 to 3.2 dB. Thus, the retrofit effectively reduces the sound exposure in real air traffic and should motivate airlines to upgrade their fleet.
Name: Mr Christoph Zellmann