In the midst of testing, pilot Ivan Ivashchenko was killed when his aircraft developed flutter which tore off his horizontal tail, causing a spin and crash on 17 March 1950. Lack of wing stiffness also resulted in aileron reversal which was discovered and fixed. Construction and tests of additional prototypes "SI-2" and experimental series aircraft "SI-02" and "SI-01" in 1951, were generally successful. On 1 September 1951, the aircraft was accepted for production, and formally given its own MiG-17 designation after so many changes from the original MiG-15. It was estimated that with the same engine as the MiG-15's, the MiG-17's maximum speed is higher by 40–50 km/h, and the fighter has greater manoeuvrability at high altitude.