An Accel Synchro Summon is a method of Summoning an Accel Synchro Monster. This variant of Synchro Summon is used in the Yu-Gi-Oh! 5D's anime and was first seen in Episode 74, performed by Bruno while in his identity as Vizor.
When performing an Accel Synchro Summon, the required Synchro Material Monsters must be themselves Synchro Monsters. As usual, 1 Tuner Monster and 1 or more non-Tuner monsters are required; this effectively makes the requirement 1 Tuner Synchro Monster and 1 or more non-Tuner Synchro Monsters. In order for it to count as an Accel Synchro Summon, the summoned Synchro Monster itself must require a Synchro Tuner and a Synchro Non-Tuner. This is due to the fact that an Accel Synchro Monster is a different kind of monster from an ordinary Synchro Monster in the anime, but are changed to be normal Synchro Monsters with such summoning conditions in the TCG/OCG.
In the 5D's anime, an Accel Synchro Summon can only be successfully performed when the user is in a state of Clear Mind. Accel Synchro Summoning can be performed even during the opponent's turn. In the anime, this ability is an inherent property of Accel Synchro Monsters (which are classified as a sub-division of regular Synchro Monsters). However, this ability is due to the effect of Synchro Tuner Monsters in real life as Accel Synchro Monsters aren't a separate class of monster. When such a Summon is performed in the anime, the user and the Synchro Materials are shown to rapidly accelerate, briefly vanish, and then reappear behind their opponent along with their new Accel Synchro Monster.