what can only be understood in the light of the turmoil? I don't understand the last sentence.
Mac had reacted quickly. The flight to Washington, he realized, would have to be postponed. He had headed for Swindal, and as he darted forward he must have passed McHugh—one of several near misses for Godfrey, which can only be understood in the light of the turmoil in the staff area.

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Answer

'Understood in the light of' - something figuratively 'illuminates' the situation - i.e. it makes it clear. 
'the turmoil' is referring to lots of things happening, noise, and people coming and going. 
So - it means that ' the general confusion explains why'...