Saturn has responded to quickly to questions raised about the 117S engine after a flame-out on Sunday forced Sukhoi T50-2 test pilot Sergei Bogdan to execute a rather hasty take-off abort procedure. It didn’t help that the starboard engine flame-out occurred in front of about 200,000 witnesses at the MAKS air show hoping to catch a glimpse of Russia’s premier new stealth fighter.
The 117S is one of the key innovations supporting both the Su-35 and PAK-FA prototpye programmes. The new engine boosts thrust compared to the Saturn Al-31FP by 16% to 14,500kgf in maximum reheat for the SU-35BM, and perhaps even higher for the PAK-FA version. (Jane’s also has reported that Russia has agreed to transfer the Saturn/UMPO 117 to AVIC for the J-20.) And it introduces a digital engine control system fully integrated with the T50 prototype’s flight control system. It appears to be the latter feature that caused the engine breakdown, according to Flightglobal’s Moscow-based correspondent Vladimir Karnozov, who writes today:
Speaking to Russian media two days after the incident, NPO Saturn general director Ilya Fedorov acknowledged that the starboard Item 117 “suffered surge”.
According to Fedorov, this happened due to a malfunctioning multi-parameter sensor, at some point of time it began feeding “erroneous data” to the airplane’s control system. He thanked Sukhoi test-pilot Sergei Bogdan for prompt reaction to the engine failure. “It was a test for the new machine. During flight trials on any brand-new aircraft – and this airplane is undergoing flight trials – malfunctions such as this one are not only possible, but even mandatory”. Fedorov stated that flight trials are meant for finding and eliminating any would-be malfunctions “so that these do not happen after the new type becomes operational”.
Fedorov further insisted that “the motor did not fail – in fact, it was put by erroneous control input into a wrong mode that caused surge… this is not an engine failure, but the wrong data input caused by a malfunctioning sensor feeding data to the flight control system”. Saturn head further insisted that the T50-2 starboard engine “is intact”. “After what had happened, the motor was checked with dedicated equipment, the malfunctioning sensor was replaced by a good one. Today, there is no issue with this engine”.