Underwing icing
The new generation Diamond DA42, of flying school use, can be equipped for FIKI with "wet wing" porous leading edges and glycol flung onto propeller leading edges.
It is quite a shock when the speed drops from 140 to 120 upon first encountering ice, with all systems running normally.
If the speed goes below 120, ice can begin to accumulate on the underside of the fuselage and on other unprotected surfaces. This has a further decelerating effect.
This aircraft really is just equipped with a "get out of icing conditions" system, despite being certified for continuous flight in light to moderate icing conditions.