The fuel cells could be used as auxiliary power units to produce electricity when an aircraft is on the ground, for example, allowing its engines to be turned off.

燃料电池可以当做辅助供电单元使用，比如，当飞机在地面时，可以允许关闭飞机发动机。

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A sonic boom is the thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound or supersonic.

音爆是当飞机或其它类型的飞行器以超音速飞过头顶时，地面上的人听到的类似雷声的噪音。

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It starts with sessions on the ground with British Airways pilots who explain the technical side of flying, including how an aircraft operates and what causes turbulence.

课程一开始，由英航飞行员讲解飞行技术，包括飞机如何操作，以及颠簸是如何导致的等等……

youdao

The fuel cells could be used as auxiliary power units to produce electricity when an aircraft is on the ground, for example, allowing its engines to be turned off.

ECONOMIST: Electric planes

In a second category A case, which was reported recently by the Air Accidents Investigation Branch, a departing BAe 146 aircraft almost collided on the ground with an arriving two-seater Piper aircraft at Birmingham airport.

BBC: Jet in near miss mid-air collision

An engine failed during tests on the ground in South Carolina last July and inspectors found a similar problem on another aircraft in September.

CNN: Airline: Dreamliner fuel leak due to an open valve