Show the fleet series of the aircrafts flied by pilots younger than 34
SELECT T2.Fleet_Series FROM pilot_record AS T1 JOIN aircraft AS T2 ON T1.Aircraft_ID  =  T2.Aircraft_ID JOIN pilot AS T3 ON T1.Pilot_ID  =  T3.Pilot_ID WHERE T3.Age  <  34
fleet series of aircrafts refers to Fleet_Series; pilots younger than 34 refers to WHERE Age < 34; flied by pilots indicates a JOIN condition between pilot and aircraft tables;