The VISh-23Ye propeller was delayed, and early test runs were conducted using a different propeller with manual pitch control (VISh-3Ye). Consequently, the engine was prone to overheating, and to compensate for this the cowling flaps restricting airflow around the engine were removed. Despite these problems, and the fact that the prototype had not completed all ground tests, the authorities were demanding a test flight as soon as possible. Polikarpov himself objected to flying the prototype before it would be ready, around February 1939, but he could not stop it. The series of events which took place on 15 December 1938, while not entirely clear, are tragic. Neither Polikarpov nor Tomashevich approved the initial flight, and no one had signed the form releasing the prototype from the factory. The famous Soviet test pilot Valery Chkalov took off and made a low-altitude circuit around the airfield. For the second circuit, Chkalov flew farther away, climbing to over 2,000 m (6,560 ft), even though the flight plan specifically forbade exceeding 600 m (1,970 ft). Chkalov apparently miscalculated his landing approach and came in short of the airfield but, when he attempted to correct, the engine stalled. The pilot was able to avoid several buildings but crashed into a power line. Chkalov was thrown from the cockpit, badly injured, and died two hours later.