14 CFR § 141.38 - Airports.
(a) An applicant for a pilot school certificate or a provisional pilot school certificate must show that he or she has continuous use of each airport at which training flights originate.
(b) Each airport used for airplanes and gliders must have at least one runway or takeoff area that allows training aircraft to make a normal takeoff or landing under the following conditions at the aircraft's maximum certificated takeoff gross weight:
(1) Under wind conditions of not more than 5 miles per hour;
(2) At temperatures in the operating area equal to the mean high temperature for the hottest month of the year;
(3) If applicable, with the powerplant operation, and landing gear and flap operation recommended by the manufacturer; and
(4) In the case of a takeoff -
(i) With smooth transition from liftoff to the best rate of climb speed without exceptional piloting skills or techniques; and
(ii) Clearing all obstacles in the takeoff flight path by at least 50 feet.
(c) Each airport must have a wind direction indicator that is visible from the end of each runway at ground level;
(d) Each airport must have a traffic direction indicator when:
(1) The airport does not have an operating control tower; and
(2) UNICOM advisories are not available.