 The type suffered a number of in-flight explosions, eventually traced to poor insulation between the aircraft's engines and fuel tanks in the rear fuselage - overheating of these tanks could cause fuel explosions.This was eventually partly solved by fitting a metal heat shield between the engines and the tanks.The aircraft's elevators proved ineffective at supersonic speeds, and an all-moving slab tail was tested by the second and third SM-9 prototypes, and later included in the major production type, the MiG-19S, which also featured an improved armament.