Summary
This document proposes to adopt a new airworthiness directive (AD) that would apply to the Burkhart Grob, Luft-und Raumfahrt (Grob) Model G 109 sailplanes. The proposed action would require installing a damper and new bell crank lever on the rudder, in addition to adjusting the weight and balance of the sailplane, to correct the tendency of flutter at specific excitation frequencies. For those Grob G 109 airplanes that have previously accomplished this installation, a proposed modification to the damper and bell crank lever, and adjusting the weight and balance would be required. The proposed action is prompted by the discovery of rudder vibration problems during testing of two Model G 109 sailplanes. The actions specified by the proposed AD are intended to prevent the oscillation of the rudder, which could result in structural damage and eventual loss of control of the sailplane.