The present invention relates to a method of protecting an aircraft in approach by signalling against the risks of collision with the terrain in steep-sided environments, in order to avoid unwanted warnings emanating from the clearance sensors of the onboard TAWS system while protecting the aircraft when it fails to observe the published procedure, and this equally in a landing procedure and in a take-off procedure. The method includes conferring an additional function on the conventional TAWS functions, specific to the detection of the potential risks of collision of the aircraft with the terrain when following procedures of reduced protection corridor type, and this without modifying either the logics or the characteristics of the clearance sensor or sensors as currently defined in the TAWSs of the state of the art.