subsonic airplane

例句：

1. 1.The aircraft was flying 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.
   发动机的声音几乎低于噪音水平。
3. 3.The pilot had to make an emergency landing due to the subsonic speed.
   由于亚音速速度，飞行员不得不紧急降落。