On aircrafts with fully mechanical operated flight controls, there is a risk of a flight control surface jam after treatment with de-icing fluid. This can happen, if fluid residues remain in the small gaps between the surface and the control flap wich is moved by the pilots. At higher altitudes the fluid residues in combination with humidity can freeze and block the tabs. On the BAe146/RJ for example, the elevators and ailerons are affected. We have to inspect and clean these flight controls after a certain time, if the aircraft has received a de-icing treatment with fluid
II or
IV.
As you can not clearly identify dry residues, you have to spray some warm water on the surfaces. Then wait approx. ten minutes. De-Icing residues will form a gel in combination with water. They consist of a thickening agent wich remains after all glycol is evaporated. If something was found, you have to carefully clean everything before releasing the aircraft to service.