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 This summer, the fourth flying prototype of the Sukhoi PAK FA (T-50) fifth-generation advanced tactical fighter joined the factory flight tests being flown at Sukhoi's flight test facility in Zhukovsky, Moscow Region. Together with the third prototype, it is used mostly for flight testing of the fighter's cutting-edge avionics suite – an advanced Tikhomirov-NIIP AESA airborne radar in the first place, a sophisticated IRST system and other systems as well.
The PAK FA's fourth flying prototype, the T-50-4, was completed in Komsomolsk-on-Amur in late autumn last year. Sukhoi's test pilot Sergei Bogdan conducted the first flight on 12 December 2012 and then flew it to the Gromov LII Flight Research Institute in Zhukovsky on 15–17 January 2013 following several test flights and the painting in Komsomolsk-on-Amur. The ferry flight about 7,000 km long, which included several stopovers across Russia, went smoothly and demonstrated the high reliability o the aircraft and all of its systems. As is known, the first three PAK FA prototypes were disassembled and flown to Zhukovsky by An-124 Ruslan airlifters after their several test flights in Komsomolsk-on-Amur. The T-50-4 is the first prototype that ferried itself from the plant in the Russian Far East to the Moscow Region.
Having arrived at Sukhoi's flight test facility in Zhukovsky, the T-50-4 (side number 054) joined in March the three other prototypes involved in the flight test programme there.
The third flying PAK FA prototype's flight test phase commenced at Sukhoi's flight test station in Zhukovsky in mid-June 2012. Sukhoi's test pilot Hero of Russia Sergei Bogdan took T-50-3 prototype for its maiden flight in Komsomolsk-on-Amur on 22 November 2011. Following three sorties under the factory acceptance programme, the aircraft had been painted and airlifted by an An-124 Ruslan heavy-lifter to Zhukovsky on 28 December 2011.
The aircraft had been assembled and its systems had been debugged and ground-tested at Sukhoi's flight test facility for five months. In particular, the aircraft was for the first time equipped with an AESA radar prototype developed by the Tikhomirov-NIIP institute, and the radar's operation as part of the avionic suite was tested.
Sergei Bogdan took it to the sky at the Gromov Flight Research Institute airfield on 21 June 2012. The AESA radar tests commenced in July. First, it was tested on the ground against an aerial target. The first flight test of the AESA onboard T-50-3 in several operating modes took place on 24 July 2012. According to an official statement by Sukhoi, “the early tests of the radar's air-to-air and air-to-surface modes onboard the T-50-3 prototype have produced good stable results on a par with the performance of the best existing aircraft. Approaches to refining these capabilities have been proven. Work has begun to test the optical channels”.
To date, the T-50-3 has flown more than 50 test sorties, mostly to test the AESA radar and other avionics.
The second flying prototype, the T-50-2 (side number 052), was first flown by Sergei Bogdan on 3 March 2011. A month later it was brought to Zhukovsky, and started flying there in mid-August. In August 2012, the aircraft started being used for testing mid-air refuelling from Russian Air Force Il-78 tanker planes. Since early this year, the T-50-2 which logged more than 80 sorties by that time has been undergoing modification for trials within the expanded g-load and flight limit bracket and is to resume its flying in June.
The first flying prototype, T-50-1 (side number 051) is being used in trials too. It had spent about a year, undergoing improvements since the unveiling at the MAKS 2011 air show in August 2011. The T-50-1 first flew in Komsomolsk-on-Amur on 29 January 2010 and has been flown in Zhukovsky since April 2010. The preparation of the T-50-1 for extreme angle-of-attack and supermanoeuvrability test flights had been completed by last autumn, and its first flight in the wake of the modification took place in Zhukovsky on 11 September 2012. In all, it fulfilled more than 100 sorties by this summer
The 100th test flight under the PAK FA test programme was performed in November 2011, with the 200th flight took place in January 2013. This year, the fifth aircraft is to join the trials. T-50-5 is under assembly at the plant in Komsomolsk-on-Amur now. It will be followed by the sixth example.
As many as five Sukhoi test pilots have been flying the T-50s: in addition to Sergei Bogdan, who performed the maiden flights on the four prototypes being tested, they are Roman Kondratyev, Yuri Vashchuk, Sergei Kostin and Taras Artsebarsky.
On 25 April 2013, the first military pilot, Col. Rafael Suleimanov, a test pilot with the Defence Ministry Flight Test Centre named after Valery Chkalov, conducted his first solo flight on a PAK FA (T-50-3).
The RusAF commander Lt.-Gen. Victor Bondarev said in January that the PAK FA would start its official tests at the Defence Ministry's Flight Test Centre in Akhtubinsk in 2013. The construction of the six prototypes will be followed by the manufacture of a low-rate initial production batch for operational evaluation and then by full-rate production. According to the media, about 60 production-standard PAK FAs are planned for fielding during 2016–20. Obviously, the deliveries will continue past 2020.
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