Yesterday, May 3, a FlyOne Airbus 319 (21-year-old) returned to service, according to Flightradar24.
Right now this plane is flying 3F-312 from Moscow to Yerevan. Earlier today it already managed to take passengers from Novosibirsk to Yerevan and back, and yesterday it also flew between Sochi and Yerevan.
This airliner has not flown since March 18. As a reminder, FlyOne is currently frequently adjusting its schedule, so keep track of possible changes to your reservation on the airline's website.
Source