An improvement and method for improved structural dynamic stability for 20 and 30 Series Learjets are disclosed. The improvement includes a redistribution of the elevator mass balance to uncouple the elevator rotational motion from the stabilizer translation motion for the higher order horizontal frequencies having node lines in the proximity of the mass outboard counterbalance weights. The original tail section includes a rudder, and a horizontal stabilizer supporting an elevator mounted adjacent the rudder. The elevator includes a proximal end adjacent the rudder and a distal end that includes a counterbalance portion. The improvement includes replacement of an original mass counterbalance weight from within the counterbalance portion with a new mass counterbalance weight of less mass, and the inclusion of additional mass counterbalance weights disposed within the elevator and interposed between the proximal end and the counterbalance portion.