Originally Posted by TerryK

Many GDS and airlines systems can only accommodate 4-digit flight numbers. This will require massive amount of system upgrades across GDS and all airlines worldwide, not just *A as other airlines can interline to *A too. Tickets need to be redesigned too as current ATB only allows 4-digit. Yes, paper tickets still exist in parts of this world. The trouble with changing airlines systems is that it needs to be uniform worldwide for interlining.