Russia and the USN already downed civilian airliners.
The Israelis also downed an airliner.
Plus there is the rumor of the Italian airliner accidently shot down by a USN fighter who was practicing intercepts back in the 80s.
Then there was the New Mexico Air Guard F100 that shot down the B52 with a Sidewinder in 1961 and the F14 that bagged an RF 4 in Europe.