The first thing that happens on arrival (unless MD83 or similar) is that the nose gear is chocked. Once engines shut down and anti collision beacon switched off, the the main gear are chocked (varies on the configuration between companies and aircraft type). The cones are placed to produce a "circle of safety" around the aircraft - equipment is then not allowed to drive between the cone and aircraft - i.e. cones at wing tips SHOULD ensure no-one drives under the wing and so on... not just for high vehicles... additionally if the aircraft is day or night stopping, the cones remain and all equipment is removed outwith the "circle" once all doors etc have been closed
Cheers,
JFF
