Two planes collided in mid-air and crashed at Saskatchewan Air Show, Canada, in 2005

What happens in this video ?

On July 10th 2005, three planes (a Waco UPF-7, a Wolf-Samson and a Pitts) were engaged in a simulated dogfighting display at Moose Jaw / Air Vice Marshal C.M. McEwen Airport as part of the Saskatchewan Air Show (a ground display featuring a jet-powered truck called Shockwave was part of the act).
During the execution of a series of crossing , the Waco and the Wolf-Samson collided near show centre. Both biplanes caught fire and crashed. Both pilots were killed at impact, and both aircraft were destroyed. All debris fell away from the crowd.