Helicopters are expensive and delicate machines requiring heavy maintenance, especially when flying in dusty conditions.

直升机是昂贵而易损的机器，需要精心保养，尤其是在尘土飞扬的条件下飞行时。

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Helicopters are expensive and delicate machines requiring heavy maintenance, especially when flying in dusty conditions.

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His mechanics now take each plane apart once a year for heavy maintenance.

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Two were in various stages of a heavy maintenance period, and one was in a Refueling Complex Over-Haul (RCOH) period.

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