Nevertheless, work on the I-180 continued. The second prototype I-180-2 with a bigger wingspan of 10.09 m (33 ft 1 in) and M-87A engine flew on 27 April 1939, and participated in the May Day parade a few days later. Later, the engine was changed to the M-87B and the wing construction was strengthened. The prototype demonstrated a top 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.