Mo. Rev. Stat. § 305.320
Wherever revenue bonds are issued and outstanding under sections 305.315 and 305.317 inclusive, all of the income and revenues received from the operation of the airport or airports, and related facility or facilities, pledged to secure the payment of the interest and principal of such bonds shall be deposited in a separate fund which shall be used only in paying the principal and interest of these revenue bonds and reserves therefor and the cost of rental, maintenance, operation and depreciation of such airport or airports, and related facility or facilities, to such extent and in such order of priority as shall be provided by the respective resolutions authorizing revenue bonds; provided, however, no priority accorded by such a resolution may be impaired by a subsequent resolution authorizing revenue bonds unless specifically so permitted by a covenant of the kind authorized to be included in a resolution by section 305.317. Such income and revenues in excess of requirements for payment of principal of and interest upon these bonds and reserves therefor and for payment of cost of maintenance, operation and depreciation of the airport or airports, and related facility or facilities, may be used for rehabilitation, reconstruction and expansion of existing airports and related facilities, or for the retirement of any outstanding bonds issued for airport purposes. After all such bonds have been paid, such income and revenues may be transferred to the general corporate fund of the authority and be used for maintenance, operation, repair and development of such airport or airports, and related facility or facilities, or for any other corporate purpose.
§ 305.320, RSMo