One of about ten Russian Su-35 experimental fighters crashed outside of Moscow on December 20th. The Su-35 is a modified version of the Su-27. Both aircraft are roughly equivalent to the American F-15. But the Su-35 was given better electronics and thrust vectoring, which made it the most agile jet fighter in the world. The Su-35 is also equipped to attack ground and naval targets. The aircraft is seen as a cheaper rival for the superior F-22.  Russia has been unsuccessful, so far, in selling the Su-35 to anyone, and the Russian air force cannot afford to buy them. China is the most likely customer, but is insisting on getting a lot of unique manufacturing technology the Russians don't want to part with.