A malfunction in the automatic flight control system was the cause of the Sukhoi PAK-FA's starboard engine flame-out at the MAKS Moscow air show, according to Russian engine maker NPO Saturn.
Speaking to the Russian media two days after the incident, NPO Saturn general director Ilya Fedorov acknowledged that the starboard engine "suffered [a] surge".
A bright flame was seen to erupt from the powerplant when the fighter was halfway through its take-off run at Ramenskoye airfield on 21 August. According to Fedorov, this was due to a malfunctioning sensor which began feeding "erroneous data" to the airplane's control system.
© Ivan Stepanov
He thanked Sukhoi test pilot Sergei Bogdan for his prompt reaction to the engine malfunction. "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 said: "The motor did not fail - in fact, it was put by erroneous control input into a wrong mode that caused the surge. This is not an engine failure, but the wrong data input caused by a malfunctioning sensor feeding data to the flight control system.
"After what had happened the motor was checked [and] the malfunctioning sensor was replaced by a good one. Today, there is no issue with this engine."