Md. Code, Transportation § 5-611

(a) To facilitate the enforcement of airport zoning regulations adopted under this subtitle, a political subdivision may establish a system and adopt rules and regulations for the granting of permits to:

(1) Establish or construct any new structure;

(2) Make any new use of any existing structure or land;

(3) Substantially alter any existing structure or use of land; or

(4) As to any tree or other vegetation:

(i) Plant or replant any of such a height as to be an airport hazard;

(ii) Allow any to grow to such a height as to be an airport hazard; or

(iii) Even if it is nonconforming, allow any that is an existing airport hazard to grow any higher.

(b) (1) Whether or not a permit system is established under subsection (a) of this section, before any work is started to substantially alter any nonconforming structure and before any growth described in subsection (a) of this section is allowed of a tree or other vegetation, a permit shall be obtained from the administrative agency authorized to administer and enforce the zoning regulations.

(2) The administrative agency shall issue a permit as a matter of right for the replacement or alteration of a nonconforming use or structure, except that the agency may not issue any permit that will allow a structure or tree or other vegetation to be higher than or to be a greater hazard to air navigation than it was when the applicable airport zoning regulation was adopted.

(c) If the administrative agency grants a permit under this section that does not have to be issued as a matter of right, it may condition the permit so as to require the owner of the land or structure to which the permit applies to install, operate, and maintain at his expense the markers and lights necessary to indicate to aircraft the presence of an airport hazard.