Whenever the Department makes an order granting or denying a certificate of approval of an airport or a restricted landing area site, or an original license to use or operate an airport, restricted landing area or other air navigation facility, and the applicant or any interested political subdivision, within 15 days after notice of such order has been sent to the applicant by registered mail, demands a public hearing, or whenever the Department desires to hold a public hearing before making an order, such a public hearing in relation thereto shall be held in the political subdivision applying for the certificate of approval or license, or in case the application was made by anyone other than a political subdivision, at the county seat of the county in which the proposed airport, restricted landing area or other air navigation facility is proposed to be situated, at which hearing parties in interest and other persons shall have an opportunity to be heard. Notice of the hearing shall be published, at least twice, by the Department in a legal newspaper of general circulation in the county in which the hearing is to be held, the first publication to be at least 15 days prior to the date of hearing. After a proper and timely demand has been made the order shall be stayed until after the hearing, when the Department may affirm, modify or reverse it, or make a new order. If no hearing is demanded as herein provided, the order shall become effective upon the expiration of the time permitted for making a demand. Where a certificate of approval of an airport or restricted landing area site has been issued by the Department, it may grant a license for operation and use, and no hearing shall be demanded thereon.