What is a flying change of lead in dressage?

A flying change of lead is a movement in which the horse changes its canter lead — switching from left lead to right lead or vice versa — during the moment of suspension in the canter stride, maintaining the canter rhythm without breaking to trot or walk between the two leads. The change happens in a single stride: during the moment when all four feet are off the ground in the canter's suspension phase, the horse reorganizes its footfall sequence so that the new lead's hind leg strikes the ground first, establishing the opposite lead for the following strides. A correctly executed flying change should show the change occurring simultaneously in both the front and hind legs — what is described as a clean change through — so that the horse changes both in front and behind in the same moment of suspension rather than changing in front before changing behind or changing behind before changing in front. The flying change represents a significant gymnastic achievement because it requires the horse to have sufficient straightness, balance, collection, and responsiveness to the rider's aids to reorganize its footfall sequence during a fraction of a second of suspension while maintaining the canter's three-beat rhythm, impulsion, and expression through and after the change. Single flying changes first appear in the competition program at Third Level in the United States and at Prix St. Georges internationally, reflecting the level of training development required before the movement can be correctly executed. The quality of the flying change — its cleanness, its straightness, the maintenance of rhythm and expression through the change — is evaluated by judges as a high-coefficient movement that significantly affects the test score.