Increasing air passenger traffic is a sign of increasing prosperity
check this ranking of countries by air passenger traffic india is the 4th biggest aviation market in the world
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If you are looking at economic power of a country, total air passengers carried can be one of the several indicators, albeit a weak one.
But if you are looking at the prosperity of the citizens, air passengers carried per capita makes more sense.
For Japan and China, with highly developed high speed rail system that directly competes with air travel, total air + HSR passengers carried would have been a much better indicator.