Maximum trijet mass
The heaviest twinjet is, I think, Boeing 777, with up to about 350 tons MTOW.
Probably because it is not possible for one engine to propel a bigger plane. Boeing 747 and Airbus 380 are quadjets and Mriya is a sexjet.
Can a big engine be mounted in the fin? And could a Boeing 747 or Airbus 380 derivative be built with three engines?