subsonic mode

例句：

1. 1.The aircraft is flying at a subsonic speed.
   飞机以亚音速飞行。
2. 2. The rocket will reach the moon in a subsonic flight.
   火箭将以亚音速飞行到达月球。
3. 3. The sound waves are traveling at a subsonic speed.
   声波以亚音速传播。