Decathlon 8KCAB
Flight Crew Private
Flight Crew Last 90 Days 1.9; Flight Crew Total 788; Flight Crew Type 390
Communication Breakdown; Situational Awareness
Conflict NMAC
Flight Crew Took Evasive Action
Human Factors
Aircraft X called UNICOM after engine startup and verified radio was working and received barometric pressure and reported runway winds. Pilot of Aircraft X had observed over the previous hour to flight that other aircraft were taking off and departing Runway XX.  Aircraft X then reported taxiing from hangars to Runway XX on CTAF. Aircraft X taxied past FBO noting several aircraft on ramp along with what later turned out to be aircraft 2. Aircraft X performed run-up in designated run-up area near the threshold for Runway XX. While taxiing up to threshold for departure; pilot of Aircraft X heard very broken communication from Citation with UNICOM. Aircraft X announced on CTAF that they were departing Runway XX with a downwind departure from the pattern. Aircraft X heard no other communication from Aircraft Y. On initial liftoff; Aircraft X saw Aircraft Y roll onto Runway XY and proceeded to depart runways. Aircraft X took evasive action banking to the right while climbing but staying below pattern altitude as [Runway] XX is right-hand traffic. After stabilizing the aircraft from the maneuver Aircraft X called Aircraft Y to determine if they were able to hear Aircraft X. There was no response from Aircraft Y. Aircraft X then called UNICOM on the same frequency to see if they could be heard and received a 5 x 5 report back. Later during the short flight in vicinity; Aircraft X also called out to another aircraft who was departing ZZZ to see if the radio was working properly and received a 5 x 5 report back. Later pilot of Aircraft X visited FBO where Aircraft Y taxied from to discuss what had happened. Pilot of Aircraft X learned that Aircraft Y taxied from the ramp directly to Runway XY and departed without stopping.
Decathlon pilot reported a near mid-air collision during takeoff with an opposite direction Citation that was not communicating on CTAF.