According to Wikipedia: "The Beriev A-50 (NATO reporting name "Mainstay") is a Soviet-built airborne early warning (AEW) aircraft based on the Ilyushin Il-76 transport. Developed to replace the Tupolev Tu-126 "Moss", the A-50 first flew in 1978. It entered service in 1984, with about 40 produced by 1992."