Sukhoi's T-50 PAK-FA fifth-generation stealth fighter has completed initial approach trials to a flight refuelling aircraft, the company said on 21 August.
Aircraft T-50-2 made approaches to an Ilyushin Il-78 tanker accompanied by a Su-25UB aircraft.
Sukhoi's second prototype, T-50-2, is undergoing a range of flight trials to test the new plane's flight envelope in subsonic and supersonic regimes and in different configurations.
The first prototype, T-50-1, is being prepared for a flight-test programme involving flight at super-critical angles of attack and super-maneouvrability.
In August, T-50-3 will start full tests of the aircraft's new active phased-array radar system and avionics, which the company says has already produced impressive results in air-to-air and air-to-ground tests.
The active electronically scanned array radar will allow T-50 to attack targets at long-range in simultaneous air-to-air and air-to-surface modes, detect and classify group and single targets and simultaneously attack several targets with precision-guided weapons and perform electronic warfare functions.
A fourth T-50 will join the test programme later this year.