The Russian longstanding plan to acquire and commission its fleet of the fifth-generation multirole fighter into service by 2018–19 has been further postponed due to technological hurdles and, above all, engine problems.

Russia will not buy Su-57 in the serial configuration before 2020 and deferred mass production of the fighter for a number of possible reasons, but it hasn’t canceled the program outright.

Initially, it was expected that the contract for the serial Su-57 will be signed in 2018, but later the TASS reported that contract for serial batch of fifth-generation fighter jets to be signed in 2020.

“In 2020, we plan to sign the second contract to manufacture and deliver 13 Su-57 fighter jets, some of them equipped with the second-stage engines,” a source in Russia’s aircraft-making industry told TASS on Wednesday.

“The preliminary timeframe for the new contract is five years.”

The aircraft’s manufacturer, the United Aircraft Corporation, refrained from commenting on the report.

But a two years ago, the deputy Defense Minister Yuri Borisov made a statement at a press conference devoted to the results of the Army-2017 international military and technical forum that Russia’s Defense Ministry expects to sign a contract for a pilot batch of fifth-generation Su-57 fighter jets in 2018 and troops should receive aircraft in 2019.

“The forum’s visitors displayed great interest in the latest Russian aircraft, including Su-34 and Su-35 planes, and also the cutting-edge fifth-generation fighter jet which has been named as the Su-57,” the deputy defense minister said.

“We are now considering signing a contract for the delivery of a pilot batch of these fighter jets in 2018 with their dispatch to the troops in 2019,” he added.

According to the thedrive.com, the most immediate issue actually seems to be that the aircraft is not ready for mass production due to long-standing engine problems that might not be solved for years.

The Russians seem to have finally arrived at the conclusion that the Saturn AL-41F turbofan simply isn’t powerful enough for the Su-57. In December 2017, a Su-57 flew for the first time with the more capable Saturn Izdeliye 30.