 In late May 2011 , Sukhoi flew the first Su @-@ 35S to the Defence Ministry 's 929th State Flight Test Centre at Akhtubinsk prior to states joint tests conducted to prepare the aircraft for operational service with the VVS . Official trials commenced in mid @-@ August with the two Su @-@ 35 prototypes , before being joined by production aircraft . As of March 2012 , four Su @-@ 35S units were involved in such tests , operating alongside the two flying prototypes . These Su @-@ 35s had by April and August 2012 , completed 500 and 650 test flights , respectively . 
