In April 2017 one of four new Russian A-50U AWACs (Airborne Warning and Control System) aircraft was spotted in Syria. This U version entered service in 2011 but foreign ELINT (electronic intelligence) experts had not yet had a good opportunity to see how effective it was. To do that you have to get your ELINT aircraft close to an A-50U in a combat zone. In this case the most effective ELINT aircraft turned out to be several American F-22s stealth fighters quietly (and apparently undetected) operating over Syria. Officially the F-22s were there to perform missions where effective stealth was a requirement. That meant reconnaissance missions during periods when the Russians or Syrians were angry at the U.S. Russia had some of its most modern electronic warfare systems operational and vulnerable to close examination by American and Israeli ELINT.
The other American ELINT aircraft was several new F-35Is owned and operated by Israel. These have been seen flying near the Syrian border but no one is sure if an F-35I or two slipped across the border to join the hide and seek action the F-22s had monopolized until recently. The F-22 and F-35 have more than stealth in common. Both have impressive software that automatically operates the many passive (they don’t broadcast and reveal their position) sensors on board both aircraft. The U.S. Air Force recently admitted that the F-22 was, as was always suspected, carrying out ELINT missions (early sales efforts pointed that out). The F-35 uses a similar but different array of sensors and apparently more powerful software to control the collection and analysis of what is out there and do it in real time. The Israelis have installed a lot of their own hardware and software in the F-35I (which is why it isn’t called F-35A) and both Israelis and Americans want to see what the Israeli version of ELINT do, compared to the F-22 and, one suspects, an F-35A pretending to be Israeli for the purpose of playing with the hostile electronics found in Syria.
Having the new version of the A-50 there is a bonus. The A-50 was long overdue for an upgrade and the money wasn’t available in the 1990s, a period when most of the A-50s didn't fly much at all (because of no cash). The A-50 first entered service in 1984 and 40 were built by the time the Cold War ended. The A-50 is based on the Il-76 transport. After over a decade of development the A-50 became a growing presence in Russian air operations during the late 1980s. But many defects and deficiencies (compared to the American AWACS) were noted and an upgrade was planned, but delayed after the Soviet Union dissolved in 1991.
The inspiration for the A-50 was the U.S. Air Force E-3 AWACS, which entered service in 1977. This was a continuation of American AWACS development that began in 1944. The first AWACS appeared in 1945, when the U.S. Navy deployed radar equipped aircraft to control large numbers of airborne warplanes in combat. The Navy continued developing airborne early warning and control aircraft in the 1950s (the E-1) and replaced it with the E-2 in the early 1970s. This one is still in service.
The A-50 used less capable technology than the U.S. AWACS. The A-50 radar only had a range 200 kilometers, compared to 400 for the E-3. The A-50U uses modern (digital, rather than analog) systems and has a max range of 600 kilometers. The new computers allow far more (150) aircraft to be tracked and this is done more quickly and with fewer equipment breakdowns. Larger, flat screen displays replaced the older CRTs. The A-50U can control ten warplanes at a time, while these aircraft perform air-to-air or ground attack missions. The upgrade also included welcome crew amenities (a rest area with a galley and improved toilet) for the ten equipment operators and five flight personnel.
China bought some of the older A-50s and was so dissatisfied that they switched to a new AWACS design based on the Boeing 737-800 airliner. The 157 ton Il-76 jet is considered less reliable and more expensive to maintain than the twin engine, 79 ton, Boeing 737-800. Chinese airlines (some of them controlled by the Chinese Air Force) have been using the 737-800 since 1999 (a year after this model entered service). So no matter how much Russia upgrades the A-50 they are still stuck with an expensive aircraft to carry everything around.
The presence of modern Russian S300/S400 air defense systems in Syria, along with their own ELINT aircraft and now the first foreign excursion by the A-50U at the same time F-22s and F-35s are in the neighborhood is another reason why Russia has been rather cozy with Israel even though Russia is technically an ally of Iran and the Assad government. There are apparently understandings that the Israelis will not do anything (a long list of potential troublemaking) to embarrass Russian arms salesmen in the Middle East and elsewhere.