Exact mechanism unknown. Apparent uncontrolled rapid burning of propellant and simultaneous or near-simultaneous detonation of ejection charge. Casing and nozzle still intact, ejection charge cap shattered. Possible failure of glue holding the propellant to casing? Malfunction ruined the body tube forward of the coupler/motor block.
Motor appeared to fail catastrophically immediately at launch. Short upward flight, estimated 75ft or less on a model that is advertised to hit 900.