Downing of Russian Il-20 in Syria was absolutely an act of aggression against Syria orchestrated by the USA.
The incident was a US-orchestrated provocation.
Recurring pro-Kremlin disinformation on US and Syria. https://euvsdisinfo.eu/disinformation-cases/?text=syria&disinfo_issue=&date=
On the night of September 17-18, Syrian regime military forces shot down a Russian military plane by accident shortly after Israeli Air Force planes conducted an air raid inside Syria. All 15 crew member aboard the Ilyushin Il-20 maritime patrol aircraft were killed.Further debunking by Polygraph: https://www.polygraph.info/a/syrian-regime-forces-shot-down-russian-military-plane-by-accident/29498924.html
In Syria, the US Army officials support constant contacts with Russian officers to prevent any military accidents there between Washington and Moscow.
According to Israel Defense Forces, the Russian plane was shot down by the Syrian air defenses who pulled the trigger and launched and SAS missile at the Ilyushin Il-20. "By the time Syrian anti-aircraft missiles had been launched (when the accident took place), Israeli warplanes responsible for the overnight operation were already back within Israeli airspace".
Moreover, Russian president Vladimir Putin himself has declared that it looks "most likely in this case that it was a chain of tragic chance events, because an Israeli aircraft did not shoot down our aircraft".