An accident on Highway 23 Tuesday morning is under investigation.  The Highway Patrol reports Troy Yount, 41, of Concordia, failed to yield to a northbound motorcycle driven by William Boles, 34, of LaMonte.  Boles was flown to Truman Medical Center with serious injuries.  The accident occurred at the intersection of Highway 23 and Route PP at 6:30 a.m.  Charges are pending.