飞机的飞行高度受到机载传感器探测小角度范围内障碍物的能力的限制,所以飞机不能飞得太低。在60m高度以下,这类障碍物很多,例如电线、铁塔、高杆和拉线等,更不必说像阻塞气球拉线这样的障碍物。对直升机而言,甚至更细小的障碍物如通讯线也会对它构成威胁。现在的飞机传感器,从肉眼到雷达,探测上述威胁都很困难,特别是在夜间和恶劣天气 The flight altitude of the aircraft is limited by the ability of the airborne sensors to detect obstacles within a small angle so the airplane can not fly too low. At altitudes below 60 meters, there are many such obstacles, such as wires, towers, poles and cables, not to mention obstructions such as blocking balloons. For helicopters, even finer obstacles, such as communication lines, pose a threat to it. Current aircraft sensors, from the naked eye to the radar, are very difficult to detect these threats, especially at night and bad weather