Today pilots must zigzag along fixed air routes so they cross over the ground-based navigation beacons that are the backbone of the 30-year-old air traffic control scheme.

• 今天的驾驶员必须沿著固定的航路曲折行进，跨越地面导航信标的上空，这些信标就是已有30年历史的飞航管制方案的骨干。