To keep tabs on the traffic in the sky and make sure it stays on the right track, a whole series of overlapping control grids have been laid out around the globe.
基於經濟效益的考慮，每架飛機都想搶這個空層，也會造成「交通阻塞」的情形。「在天上，不能像陸地一樣擺個紅綠燈指揮交通，只有靠航空管制人員來安排飛機的優先順序」，民航局中正機場塔台台長王照說。