Weeping Wing is the nickname given to the TKS Ice Protection system, an airborne ice protection system wherein a glycol-based chemical is released onto the wing surface using small orifices on the leading edge of the wing. This system provides both ice formation prevention (anti-ice) and removal of ice which has already formed (de-ice).
The system is activated using a switch in the cockpit. This turns on the fluid pump, which pumps fluid out of the reservoir, through the ducting and out onto the calibrated orifices on the wing leading edge. As the fluid flows along the airstream (both on the top and bottom surfaces of the wing), a thin coat of fluid is left that protects the surface from icing. The excess fluid then leaves the wing surface and slides out behind the wing's trailing edge.