same plane has an energy consumption of 22 kWh per 100 p-km. A short-
haul Tupolev-154 travelling 2235 km with 70% of its 164 seats occupied con-
sumes 80 kWh per 100 p-km.

35No redesign of a plane is going to radically improve its efficiency. Actually,
the Advisory Council for Aerospace Research in Europe (ACARE) target
is for an overall 50% reduction in fuel burned per passenger-km by 2020
(relative to a 2000 baseline), with 15–20% improvement expected in engine
efficiency. As of 2006, Rolls Royce is half way to this engine target [36w5gz].
Dennis Bushnell, chief scientist at NASA’s Langley Research Center, seems to
agree with my overall assessment of prospects for efficiency improvements
in aviation. The aviation industry is mature. “There is not much left to gain
except by the glacial accretion of a per cent here and there over long time
periods.” (New Scientist, 24 February 2007, page 33.)
The radically reshaped “Silent Aircraft” [], if it
were built, is predicted to be 16% more efficient than a conventional-shaped
plane (Nickol, 2008).
If the ACARE target is reached, it’s presumably going to be thanks mostly
to having fuller planes and better air-traffic management.

Figure 5.5. Two short-haul trips on the greenest short-haul airline: 6.3 kWh/d. Flying enough to qualify for silver frequent flyer status: 60 kWh/d.