The third prototype, piloted by Kudrin, lost horizontal trim tab in flight the pilot managed to land the plane but refused to fly on SPB (D) prototypes anymore. TsAGI engineers and airfield staff voiced suspicion that other factors could have been involved, but these were not examined at all. Later they also blamed Lipkin, already dead, for the alleged reckless increase of speed. Investigators initially blamed the accident on Polikarpov's deputy Zhemchuzhin, who allegedly failed to fit the balance weights into the leading edges of the ailerons, causing wild flutter. Lipkin and flight engineer Bulychov, instructed to test wing flutter at an extreme 600-km/h (373-mph) diving speed, were killed in the crash the aircraft actually disintegrated in horizontal flight. On 30 June the second SPB (D) disintegrated in flight. On 2 June 1940 test pilot Mikhail Lipkin barely survived when, landing with engines out, his SPB (D) clipped a parked Tupolev SB. This flight, piloted by Boris Kudrin, occurred safely on 18 February 1940, but on 27 April 1940 the first prototype crashed for unknown causes, killing test pilot Pavel Golovin. In addition to the SPB (D) prototype, five pre-production machines were ordered even before the prototype made its first flight. The bomb bay could carry up to 800 kg (1,764 lbs) internally and an additional 700 kg (1,543 lbs) of bombs could be carried underneath the wings. It retained its predecessor's prominent canopy and nose glazing, but reduced the armament to a single 7.62В mm (0.300В in) ShKAS machine gun for the bombardier/navigator while the rear gunner had a retractable 12.7В mm (0.50В in) Berezin UB dorsal gun and a ventral ShKAS to protect the aircraft's underside. Two 783В kW (1,050В hp) liquid-cooled Klimov M-105 V12 engines were slung underneath the wings. The main gears of the conventional undercarriage retracted aft into the rear of the engine nacelles and the tail wheel retracted into the rear fuselage.

It was smaller than the VIT-2 and had a monocoque fuselage. The SPB (D) closely resembled the Polikarpov VIT-2, which had been recommended for production as a dive bomber, but the former actually was an entirely new design.

Spb wiki