 Problems with the K-15U radar and Klimov VK-9 engines forced a radical redesign of the aircraft to use the K-15M radar and, more importantly, much less powerful Lyulka AL-7F engines.This, in turn, led to the need to change "275" missiles to the lighter "275A" (although total missile weight decreased to , the warhead actually grew to ).The new airframe with a smaller fuselage and a delta wing instead of the earlier swept wing was designated La-250A.