14 C.F.R. § 101.13 – Operating limitations.

(a) Except as provided in paragraph (b) of this section, no person may operate a moored balloon or kite—
1. (1) Less than 500 feet from the base of any cloud;
2. (2) More than 500 feet above the surface of the earth;
3. (3) From an area where the ground visibility is less than three miles; or
4. (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.