As for the other incidents that have beset the type over the past few months -- a fan shaft failure on an engine, an oil leak, a windshield crack -- all can safely be put down to teething problems.
One way to increase the efficiency of a high-bypass jet engine is to turn the fan into an open rotor, a bit like returning to propellers, but using two rings of stubby counter-rotating blades.
By contrast, the engine designs for a putative Concorde 2 had a revolutionary double-fan arrangement that would have gone a long way to cutting the noise.