manual signalling

例句：

1. 1. The manual signalling system is essential for ensuring safe operations.
   手动信号系统对于确保安全操作至关重要。
2. 2.The pilot used a manual signalling device to communicate with the ground crew.
   飞行员使用手动信号设备与地面机组进行沟通。
3. 3.During emergencies, we rely on manual signalling to alert everyone of the danger.
   在紧急情况下，我们依靠手动信号来警告所有人危险。