This paper deals with the method of identifying the control effectiveness matrix in the control allocation algorithm without degrading the aircraft response. The vehicle having sufficient control authority during control allocation is excited in its null space by applying a dithering signal. In this way the vehicle response is not degraded. Identification of the control effectiveness matrix is necessary to compensate for failure, damage and modelling errors by control allocation, otherwise the control law should be robust enough to mitigate these effects from overall system response. The null space excitation could also be applied to the system with redundant controls (i.e. more actuators than control variables) for online tuning of the controller in steady state.