技师想要一台备用发动机以防万一。
The technician wanted to keep an auxiliary engine handy just in case.
备用发动机：我们能为每架飞机在中国至少提供一台备用发动机。
Spare engine: We will provide at least one spare engine ready in China for each aircraft.
我们有一台以防断电时使用的备用发电机。
当工作的这一台发生故障自动停止工作时，备用的这一台自动投入工作。
When one set goes wrong and stop, the other would be put into use automatically.
当工作的这一台发生故障自动停止工作时，备用的这一台自动投入工作。
When one set goes wrong and stop, the other would be put into use automatically.
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