A big airplane can carry a lot more than 20,000 kg (20 metric tons) total. The Antonov An-225 Mriya can carry a payload of 200 tons for 4000 km[1].
[1] https://en.wikipedia.org/wiki/Antonov_An-225_Mriya#Specifica...
[1] https://en.wikipedia.org/wiki/Antonov_An-225_Mriya#Specifica...
That said, I think someone is considering (re)starting production.