The last frontier in air travel was more than half a century ago when we went from propeller aircraft into the jet age, and it's been a long time since we had a step forward.

航空旅行的最后一个前沿领域是在半个多世纪以前，那时我们从螺旋桨飞机进入到喷气式飞机时代，而我们已经很久没有向前迈出一步了。