When an aircraft is "hot," that means it is in the final phase of an attack run, and selected weapons systems are active and ready. (The preceding phase is the "roll-in" phase, as the aircraft lines up for the run.)

There is likely a better Russian formulation, but alas, my Russian is not native. Прошу прощения.

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Note added at 25 mins (2005-03-17 05:22:36 GMT)
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In a former life, I was trained to communicate with attack aircraft to coordinate air strikes, FWIW.

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Note added at 3 hrs 36 mins (2005-03-17 08:34:01 GMT)
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The essential part about being \"hot\" is the fact that the pilot is seconds from the target, in an attack profile, and literally heartbeats away from unleashing hell. It seems to me one can be \"готов к атаке\" a lot earlier than that, but you\'re the native speaker. :^)