在雾天，飞行员只得靠仪器飞行。

In misty weather, the pilots have to fly by instruments.

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这次论证包括根据仪器飞行规则所鉴定的几架商业飞机、地域性飞机和直升机。

Several business aircraft, regional jets and helicopters certified for instrument flight rules are included in this certification.

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然而，如果飞行员持有的仪器等级在其必须持有的基本的飞行员执照等级之上，那么飞行员只能选择仪表飞行规则。

However, a pilot can only choose to fly IFR if they possess an instrument rating which is above and beyond the basic pilot's license that must also be held.

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