47 CFR 87.219 - Automatic operations.
(a) A station operator need not be present when an automated unicom is in operation.
(b) Unicoms operating in an automated mode must comply with the requirements of paragraphs (1)-(5) of this section, in addition to the requirements applicable to non-automated unicom operations.
(1) An automated unicom must transmit only in response to interrogating signals from aircraft, including but not limited to the brief keyed RF signals specified in § 87.187(y).
(2) An automated unicom must monitor the unicom frequency prior to transmission, and provide a brief delay between the aircraft's interrogating signal and the automatic unicom's response.
(3) Automated advisory transmissions must be as brief as possible, and must never exceed one minute in length.
(4) An automated unicom may not provide weather information at an airport that has an operational, FAA-certified, automatic weather facility, unless the unicom itself is certified by the FAA.
(5) If weather information is provided by an automated unicom:
(i) Weather sensors must be placed in order to adequately represent the weather conditions at the airport(s) to be served;
(ii) The weather information must be proceeded by the word “advisory;”
(iii) The phrase “automated advisory” must be included when the weather information was gathered by real-time sensors or within the last minute; and,
(iv) The time and date of the last update must be included when the weather information was not gathered within the last minute.
(c) Only one automated unicom may be operated at an uncontrolled airport. Prior to the operation of an automated unicom at an airport with more than one unicom licensee, all of the licensees at that airport must sign a letter of agreement stating which licensee(s) control the automated unicom operations, and, if control is to be shared among several operators, how that control will be divided or scheduled. The original or a copy of the letter of agreement must be kept with each licensees' station records. Within 90 days of the date upon which a new unicom operator is licensed at an airport where more than one unicom is authorized, and an automated unicom is being operated, an amended letter of agreement that includes the new licensee's signature must be signed or automated unicom operations must cease.