§ 421. Minimum altitudes for operation

Except when necessary for take-off or landing, or by special permission of the Agency, no person shall operate an aircraft below the following altitudes:

(1) An altitude that will permit, in the event of the failure of a power unit, an emergency landing without undue hazard to persons or property on the surface.

(2) Over congested areas of cities or towns, or over an open-air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet from the aircraft.

(3) An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In this event, the aircraft shall not be operated closer than 500 feet to any person, vessel, vehicle, or structure.