20.  Whenever it appears to the Minister that it is or is likely to become necessary for the safety of air navigation in the vicinity of an aerodrome or for securing the efficient operation of any aid to air navigation, whether situated at or in the vicinity of an aerodrome or elsewhere that any area should be cleared or kept clear of obstructions, he may declare the area to be a controlled area for the purposes of this Part and shall define the boundaries of that area.