This paper presents a method of detecting aircraft icing by monitoring its effects on aircraft dynamics. This paper shows that uncontrolled icing on control surfaces directly influences control effectiveness. Using data from onboard attitude and navigation sensors via highly computationally efficient algorithms, the control effectiveness is estimated, thereby detecting icing. Using actual flight test data from NASA Lewis Research Center, this paper demonstrates the ability of this method to detect the loss of elevator effectiveness that occurs with uncontrolled horizontal stabilizer icing that could result from a failed deicing boot. The method is generally applicable to loss of control effectiveness due to icing.Icing affects the aerodynamic performance of aircraft by contaminating the aerodynamic surfaces. Without anti-icing equipment icing, if sufficiently severe, can relatively quickly lead to a situation in which controllable flight is impossible. Even aircraft with anti-icing equipment are potentially susceptible to icing under certain conditions. Some turboprop aircraft that have de-icing boots on the leading edge of aerodynamic surfaces may experience wing and tailplane icing behind the de-icing boots. Moreover, de-icing boots can fail due to a variety of conditions including holes produced by rocks etc. In particular the failure of a horizontal stabilizer boot can occur under such circumstances that the flight crew is unaware of the failure.