Complex sentence: The prototype with R-7PB engines (registered СССР-06156) first flew on 3 January 1963 but crashed after clipping a perimeter fence during a maximum weight testing flight of the development program.
Split into simpler sentences: The prototype with the R-7PB engines (registered СССР-06156) first flew on 3 January 1963. It crashed after clipping a perimeter fence during the development program.