The paper presents results of wind tunnel flutter tests using a wing-aileron-tab model on which it was possible to represent any of the following tab systems; spring, geared, trim or servo. Prediction of the flutter characteristics has been made in the trim tab case using three sets of aerodynamic derivatives and fair agreement has been reached with the measured characteristics. A comparison has also been made of the measured characteristics with those predicted by the latest flutter criteria and possible modifications to the basic flutter frequency assumption used in deriving the criteria are discussed. One modification suggested is such that the basic flutter frequency is virtually dependent on the frequency in a single degree of freedom. The criterion form that results from such a single frequency approximation is investigated.