What are the aids for a flying change in dressage?

The aids for a flying change are coordinated movements of the rider's weight, legs, and reins that ask the horse to change its leading leg during the moment of suspension — and their effectiveness depends entirely on the timing of their application relative to the specific footfall of the canter stride. The aids must be applied at a very specific moment: during the stride before the suspension, so the horse can process and respond to them during the suspension that follows. The aid sequence involves: a half-halt to prepare and organize the horse's balance; a shift of the rider's weight slightly onto the new inside seat bone; the new inside leg moving to the girth position to ask for the new inside bend and lead; the new outside leg moving behind the girth to ask for the new outside lead — the same leg position as a canter depart aid; and a brief, soft opening of the new inside rein to allow the horse's head to position correctly for the new lead. The old outside rein maintains contact to prevent the horse from losing its straightness in the change, and the rider's following seat must accommodate the reorganization of the canter stride as the change happens. The most important aspect of the aids is their timing: aids applied too late in the stride will ask the horse to change after the suspension has passed, making a clean change impossible; aids applied too early will disrupt the balance of the approach stride. The weight shift is typically described as the primary aid by classical trainers who emphasize that the horse should respond to the weight change before the leg aids are applied, which reflects the ideal of a horse so well-developed in its response to the seat that the change becomes almost invisible in the quality of the rider's aids.