Figure 2.1 Three noise certification measurement points
Figure 2.2 80 dB Sound Exposure Level (SEL) contours for different aircraft that just meet the various ICAO Chapter limits
Figure 2.3 Continuous improvement in aircraft noise performance has occurred over time across various weight categories

Chapter 2 nominal limit line is based on average cumulative stringency differences between Chapter 2 and Chapter 3 adjusted for differences in reference procedures. Airbus A380 plotted for information as outside weight for LR4 (575 tonnes).

Aircraft categories as defined by ICAO/CAEP independent experts (IE)
  Description MTOW (tonnes)
RJ Regional Jet 30 - 50
SMR2 Short/Medium Range 2-engine 58 - 98
CROR Counter-Rotating Open Rotor 58 - 91
LR2 Long Range 2-engine 170 - 290
LR4 Long Range 4-engine 330 - 550
Figure 2.4 Some improvement in helicopter noise performance has occurred over time, mainly via the use of low noise tail rotor technologies
Figure 2.5 Reference Landing and Take-Off (LTO) cycle
Figure 2.6 Continuous improvement over time for engine NOX emissions performance (engines > 89 kN)
Figure 2.7 Improving average NOX margin to CAEP/6 limits for in‑production engines shown in successive versions of the EEDB