speed of 540 km/h (335 mph) and was recommended for mass production with the M-88 engine. Then, on 5 September 1939, I-180-2 piloted by Tomas Suzi crashed during high-altitude testing, killing the pilot. Again, the exact circumstances of the crash were unclear. According to eyewitnesses, the aircraft dove steeply (others claimed it fell in a spin) to 3,000 m (9,840 t) where it leveled out, then entered a spin again, leveling out once more at 300 m (985 ft). The pilot then abandoned the aircraft but did not use his parachute. No definite explanation was ever given but hypotheses include blinding of the pilot by oil from a leaking oil cooler, a heart attack, or loss of consciousness due to the failure of oxygen equipment. Preparations were carried out in 1940 to produce the first batch of 10 aircraft at Factory No.21 in Gorki, engaged in manufacturing the I-16. However, their production was extremely slow, without much attention of the aviation authorities, with the first 10 aircraft taking more than eight months. One of the reasons for this was that the local OKB led by M.M. Pashinin was designing their own I-16 based fighter, the Pashinin I-21 and factory management had devoted all of their resources to the hometown favorite, with only six brand new engineers assigned to production of the I-180. While this was being investigated, the third prototype I-180-3, powered by a more powerful M-88R engine and fitted with a stressed skin wing (replacing the I-16 type wing structure of the previous prototypes) was completed, flying on 10 February 1940. It was armed with two 12.7 mm Berezin BS and two 7.62 mm ShKAS machine guns on a common gunbed over the engine. Finally in April 1940, three aircraft designated I-180S were completed, these being similar to the I-180-3, but reverting to an open cockpit and the I-16 type wing structure. Their test flights were favorable. The new fighter resembled I-16 in agility but was more stable. Top speed was 575 km/h (357 mph). Major criticisms included the open canopy and poor build quality. It was believed that fixing these defects would raise the top speed to 600 km/h (373 mph). However, the I-180-3 prototype crashed on 6 July 1940, when it entered an inverted spin due to pilot error. The pilot was able to safely bail out. In preparation for production, Polikarpov produced the definitive I-180-5 with