(1) The main body of this publication presents standards for marking and lighting objects, which are potential hazards to the safe operation of aircraft, for the purpose of indicating their presence to pilots. The material in this appendix includes texts of laws and regulations, together with information to provide guidance in complying with these texts of laws and regulations, pertaining to such objects.

(2) Existing or contemplated structures which, by reason of their height and location relative to landing areas, constitute potential hazards to the safe operation of aircraft continually demand attention in the effort to provide and maintain maximum safety for air commerce.

(3) It is vitally important that prompt notification of the construction or alteration of towers, electric transmission and telephone lines, smokestacks, water towers, buildings and similar structures, of certain heights and distances from landing areas and civil airways, be given to the aeronautical public through notices to airmen before any such structure is constructed or altered. Achievement of this result requires the cooperation of all federal, state and municipal agencies, private industry and individuals engaged in such construction or alteration.

(4) For this purpose, regulations of the Washington state aeronautics commission have been promulgated requiring the submission of Form 426 prior to the beginning of the construction or alteration of structures falling within the prescribed limits of air activity. The limits within which construction or alteration requires the submission of the form have been set after careful study of the problem and with due regard for the maximum protection of airmen.

(5) In the case of an existing structure on which a proper notice has already been submitted, some latitude for repairs is permitted by an explanation of the term "alteration." Notice may be omitted if the alteration or alterations will not increase or decrease the height of the top or any part of the structure from that previously reported by more than 1 foot for each 500 feet, or fraction thereof, of the distance that the structure is situated from the nearest boundary of the landing area involved. However, notice must be given of any alteration or alterations increasing or decreasing the height of the top or any part of a structure by more than 10 feet from that previously reported.

(6) The information required on proposed construction or alteration is clearly explained in the Form 426 prepared for that purpose and is essentially that material needed to warn airmen of a potential hazard to air navigation. It is necessary, therefore, that all applicable questions therein be answered without exception. Copies of these forms may be obtained from the Washington State Aeronautics Commission, Boeing Field, Seattle, Washington.

(7) The distance between the nearest boundary of a landing area and the site of the construction or alteration may be measured by the use of maps, or on the surface of the earth by an automobile mileage meter, or other convenient but reasonably accurate means.

(8) The term "navigable water" as used in connection with obstructions to air navigation, denotes all water suitable for the take-off or landing of water aircraft. Other geographical features which combine hydrographic and topographic characteristics, such as marshes, swamps and bogs, come within the meaning of the term "ground" as described in the act.

(9) The state aeronautics commission desires to assist those contemplating construction which may present a potential hazard to air navigation in selecting locations for the structures which will create a minimum of interference with air operations; to recommend the proper obstruction marking and lighting to insure adequate protection to aircraft; and to minimize the possibility of damage to structures from collision by aircraft.

(10) For this purpose the commission has provided a special advisory service consisting of personnel who conduct the specific investigation of each case. This service is available upon request, which may be by letter or in person. The request should be accompanied by a complete description of the proposed construction, including the geographic coordinates and the distance and direction of the site from the nearest town; the distance from the nearest landing area; the height of the structure above the ground and the over-all height of the structure above mean sea level. A map or sketch showing the height and location of all tall structures in the vicinity should also be furnished. The investigation will ordinarily take approximately ten days because of the necessary contacts with aeronautical interests concerned. This period may be longer if the problem is a complex one, because every attempt is made by the investigators to resolve the problem with due regard to the safety factor.

(11) Interested contractors, engineers and architects should avail themselves of this service so as to prevent delays in obtaining the necessary permits for the construction.