Russia’s Sukhoi T-50 PAK-FA stealth fighter program has suffered another delay. Testing of the of the powerful new jet’s second stage engine, which was supposed to start later this year, has been pushed back to 2018.

"At the moment, works are being carried out within the framework of contacts with the Russian Defense Ministry,” United Aircraft Corporation, Sergei Korotkov told the TASS news agency. “Flight tests are underway. We plan to enter the second stage of trials next year."

The new engine was expected to make its first flight installed onboard the PAK-FA in the fourth quarter of 2017. "The first flight of the aircraft with the new engine is expected in the fourth quarter of 2017," a United Engine Corporation spokesman told TASS earlier in the year.

The next-generation Saturn izdeliye 30—sometime referred to as the izdeliye 129—are the engines for the T-50. There are few details available about the izdeliye 30 engines, but the new powerplant is expected to deliver 24,054lbs dry thrust and 39,566lbs of afterburning thrust.

With the new engine installed, the PAK-FA should be able to offer kinematic performance comparable to the Lockheed Martin F-22 Raptor—cruising without afterburner at speeds exceeding Mach 1.5 with a maximum speed greater than Mach 2.0 at altitudes of around 60,000ft. “Performance-wise it certainly looks to compete with the Raptor,” one senior military official with extensive experience on U.S. fifth-generation fighters told me some time ago.

Overall, while the Russians place less emphasis on stealth while focusing more on maneuverability and raw kinematic performance, the new Sukhoi-built jet appears to have a comprehensive suite of avionics. “The analysis that I have seen on the PAK-FA indicates a pretty sophisticated design that is at least equal to, and some have said even superior to U.S. fifth-generation aircraft,” former U.S. Air Force intelligence chief Lt. Gen. Dave Deptula told me a few years ago. “It certainly has greater agility with its combination of thrust vectoring, all moving tail surfaces, and excellent aerodynamic design, than does the F-35.”

But while the Russians have developed active electronically scanned array(AESA) radars, infrared sensors and excellent electronic warfare systems, one of the big questions that remain is how well the Russians have integrated the jets’ avionics. It took the United States decades of effort and billions of dollars to develop the complex integrated avionics suite and sophisticated pilot vehicle interfaces that make the Raptor the fearsome weapon that it is.

Ultimately, the Russians will probably be able to resolve technical glitches with the PAK-FA and field a capable operational aircraft. There is little doubt about that. The real question is when that will happen and how many jets the Kremlin can afford to buy.

Dave Majumdar is the defense editor for The National Interest. You can follow him on Twitter: @davemajumdar.

Image Credit: Creative Commons.