If Chox are placed next to tyres, during Mod or Hi powered eng runs, they tend to allow the base of the tyres to reduce contact with the surface on the ground and will allow the aircraft to move.
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Best option during hi-powered eng runs is big chox placed a few inches infront of tyres and a person outside and inside the aircraft looking to see if aircraft is moving, if aircraft moves they should advise person in control of engines to reduce power.
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All very simple.
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Chox use has reduced over the years, expect more of the above.
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Cheers.......