It is important to read between the lines. It took 6 years for extension of previous model to turn into production design. Then it was dropped on comrades from

It is important to read between the lines. It took 6 years for extension of previous model to turn into production design. Then it was dropped on comrades from a fellow Socialist country in a typical fashion of “intensifying economic development” (i.e. investing in specific industries in exchange for loyalty). Then it took 6 years again for actual planes to come out of factory, and become certified. And it wasn't a Concorde. The project was really low on the list either on the demanding side, or on the supplying side, or on both sides (remember that in “planned” — single big corp — economy, you might be assigned a useless work if it has been decided once, and got into the papers).