The Beriev A-50 (NATO reporting name: Mainstay) is a Soviet airborne early warning and control (AEW&C) aircraft based on the Ilyushin Il-76 transport. Developed to replace the Tupolev Tu-126 "Moss", the A-50 first flew in 1978. Its existence was revealed to the Western Bloc in 1980 by Adolf Tolkachev. It entered service in 1985, with about 40 produced by 1992. Description The mission personnel of the 15-man crew derive data from the large Liana surveillance radar with its antenna in an over-fuselage rotodome, which has a diameter of Detection range is for air targets and for ground targets. The A-50 can control up to ten fighter aircraft for either air-to-air intercept or air-to-ground attack missions. The A-50 can fly for four hours with a range of from its base, at a maximum takeoff weight of . The aircraft can be refuelled by Il-78 tankers. The radar "Vega-M" is designed by MNIIP, Moscow, and produced by NPO Vega. The "Vega-M" can track up to 150 targets simultaneously within . Large targets, like surface ships, can be tracked at a distance of . Development work on a modernized version, the A-50U, began in 2003; state tests started on 10 September 2008, using a Russian Air Force A-50 "37 Krasnyy" as a prototype. It replaces analog avionics with a new digital avionics suite, made by Vega Radio Engineering Corporation, that speeds data processing and improves signal tracking and target detection. Crew rest, toilet and galley facilities are also included in the upgrade. After completing the joint state tests, Beriev has delivered the first A-50U to the Russian Air Force. The aircraft, "47 Krasnyy'"RF-92957, was handed over at Beriev's facility in Taganrog on 31 October 2011. It was accepted by an aircrew serving with the 2457th Aviation Base for Combat Operation of Airborne Early Warning Aircraft (Aviabaza Boevogo Primeneniya Samolyotov Dal'nego Radiolokatsionnogo Obnaruzheniya) at Ivanovo Severny, which is the only base using the A-50 operationally (it operates 16 aircraft). The fourth A-50U, "41 Taganrog", was delivered to the Russian Aerospace Forces on 7 March 2017. The fifth A-50U, "45 Krasnyy", was delivered on 6 December 2018. 7 aircraft have been delivered as of December 2021. The A-50U upgrade forms the basis of the concept for Beriev A-100 AEW&C. Its configuration will be similar, but with a new Vega Premier active electronically scanned array radar. Usage and incidents In late December 2015, the A-50 started