What route has the highest demand?

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LHR-CDG is pretty huge demand

ATL - ORD has 3737Y, 522C, 87F. I don't know if that's the biggest.

ATL-ORD, then probably ATL-DFW, ATL-LAX as far as I know, and then combinations between those and between JFK, DEN, SFO.

Highest demands on Asian and European routes are lower by some 1000 Y pax compared to ATL-ORD, more comparable to something like DEN-SFO.

Anyway, use route and airport tools and you will get the picture soon.

I find Madrid-Barcelona pretty big. Any 2 big cities within Europe and US (and maybe China) will be reasonably high on the list.

There's no "maybe" about China if you compare it to Europe.

Many other destinations all around Asia (if you don't count sparsely inhabited Central Asia and Siberia) also have huge demand.

But nothing compares to biggest routes in the US by a margin of some 25-30%.

Most I`ve seen is ATL-ORD. Any other route is maybe 500 lower (depending on the season).+