 The unarmed second prototype was completed on 19 May , but did not make its first flight until 26 May . It was later discovered to have several major defects , including an oil leak from the VRDK compressor 's sleeve . The VRDK 's designer was summoned in an attempt to solve its problems although not all of these were design issues . The first prototype was grounded for most of June to remedy magneto problems and to add extra air intakes to cool the spark plugs . It attained a speed of 820 km / h ( 510 mph ) at 6 @,@ 700 m ( 21 @,@ 982 ft ) on 3 July . Unfortunately its port tailplane failed at low altitude two days later , killing the test pilot , Alexandr Deyev , when his parachute failed to open in time . Post @-@ crash analysis revealed that he had exceeded the airframe 's G limit while maneuvering . 
