A quick search of Morton's Martini AZ of Fencing and Evangelista's The Encyclopedia of the Sword reveals that the word "flying" has been used to describe a variety of blade and footwork actions over the last 200 years, ranging from parries to fleches. Maitre d'Armes Claude La Marche, one of the founders of the epee as a fencing discipline, adds to the list the "flying guard." In doing so, he harks back to a technique taught by Laboessiere fils and recommends it for the epee fencer of the 1880s and 1890s.
The Flying Guard is intended to achieve three tactical goals:
1. To close the distance with an opponent who believes himself or herself to be at a distance that makes an attack unilaterally,
2. To disguise the effort to close the distance, and
3. To allow a fast attack once a suitable distance is reached.
The Flying Guard is executed by:
1. Coming on guard, ready for offense or defense.
2. Taking several very small steps, each ending with an appel. These appels are taken to ensure that the fencer keeps balance and that the legs are ready to act. At the same time the weapon is held in a relaxed manner to ensure a fast reaction if needed.
3. Then make a loud appel combined with a shout to distract the opponent, as you
4. Bring the rear foot forward, keeping the leg well bent to avoid any body movement that would dislose the change in foot position, to close up to the front foot (gaining approximately 7 inches of distance), and
5. Execute the attack with a lunge.
It is an uncommon thing to think of a guard as being "flying," especially when compared to other uses of the term in fencing. In this case, the series of step-appel-step-appel-step-appel looks to be slower rather than faster. However, this action does provide an interesting combination of two of the uses of the appel, as a balance check and as a distractor.
The flying guard must be viewed in the context of epee at the time (La Marche warnings that half lunges would usually suffice to carry the attack forward) and of the broder practice of classical footwork. We know from accounts of professional bouts that the appel and shout combination was used in the 1870s and 1880s. Combined with the distance steal of bringing the rear foot forward, this makes the flying guard an interesting action worth practicing for the required coordination and as a surprise action that might be useful once in a classical bout.