The T-50's maiden flight has been repeatedly postponed since early 2007 for unspecified reasons.
However, in August 2009, Russian Air Force Chief Alexander Zelin said that there were problems with the engines and research was ongoing.
The PAK FA is believed to possess advanced avionics, stealth capability, a ferry range of 4,000 to 5,500 km, and endurance of 3.3 hrs; it is armed with next-generation air-to-air, air-to-surface, and air-to-ship missiles, and has two 30-mm cannons.
NIZHNY NOVGOROD, December 8 (RIA Novosti)