subsonic aircraft

例句：

1. 1.The aircraft is traveling at a subsonic speed.
   飞机以亚音速飞行。
2. 2.The sound of the engine was barely above the noise level of the road.
   发动机的声音几乎与道路噪音一样大。
3. 3. The pilot had to make an emergency landing due to the subsonic speed.
   由于超音速以下的速度，飞行员不得不紧急降落。