(Am IR pilot) Assuming someone is paying any attention, the autopilot suddenly nosing down and the vertical speed increasing would immediately result in missed approach procedures being executed. These approaches usually terminate at a pre-determined height (decision height) which unless you're flying CAT-IIIC (not really used) is minimum around 50ft and more commonly between 100 and 200ft. Therefore you have some room for error in the event something bad happens. Additionally, approach paths won't have any protruding objects within a certain range of the runway.