Currently, at least five prototypes are being used for flight testing, according to Sukhoi.
T-50 will become the first operational stealth aircraft for the Russian Air Force and will incorporate advanced avionics and all-digital flight systems.
"The program is developing as scheduled. The three additional models joining flight tests will significantly expand the test program currently underway," the UAC head said.
Speaking to reporters at the 51st Paris Air Show at Le Bourget Airport, Slyusar ruled out "any obstacles that would halt the program or push it back a few steps."
The PAK FA stealth multirole fighter is set to rival the US Air Force's F-22 Raptor, the only fifth-generation fighter currently in service, and F-35 Lightning II, which is in testing.
