Section 101.13 - Operating limitations(a) Except as provided in paragraph (b) of this section, no person may operate a moored balloon or kite-(1) Less than 500 feet from the base of any cloud;(2) More than 500 feet above the surface of the earth;(3) From an area where the ground visibility is less than three miles; or(4) Within five miles of the boundary of any airport.(b) Paragraph (a) of this section does not apply to the operation of a balloon or kite below the top of any structure and within 250 feet of it, if that shielded operation does not obscure any lighting on the structure.