Passenger capacity and the cruising speed of airplanes display clear sigmoidal (saturation) curves. Improvements in operating efficiency of jetliners (energy required per pkm or per seat) show linear improvements with the shift from early turbojets to the latest turbofans. And the growth of worldwide air traffic (in pkm) has seen exponential growth averaging 5.4%/year between 1970 and 2016, with a significantly slower rate (3.7%) expected between 2016 and 2035. Most people still want to fly more, but, inevitably, another S-curve is forming.
