D.C. Code § 9-916
In the discretion of the Authority any bonds issued under the provisions of this chapter may be secured by a trust agreement by and between the Authority and a corporate trustee, which may be any trust company or bank having the power of a trust company within or without the District. The trust agreement or the resolution providing for the issuance of the bonds may pledge or assign the fees and other revenues to be received, but shall not convey or mortgage the airports or any part of the airports. The trust agreement or resolution providing for the issuance of the bonds may contain provisions for protecting and enforcing the rights and remedies of the bondholders as may be reasonable and proper and not in violation of law, including covenants setting forth the duties of the Authority in relation to the acquisition of property and the construction, improvement, maintenance, repair, operation, and insurance of the airports, the rates or fees or other charges to be charged, and the custody, safeguarding the application of all monies. It shall be lawful for any bank or trust company incorporated under the laws of the District that may act as depositary of the proceeds of bonds or of revenues to furnish indemnifying bonds or to pledge securities as may be required by the Authority. Any trust agreement may set forth the rights and remedies of the bondholders. In addition, any trust agreement or resolution may contain other provisions the Authority considers reasonable and proper for the security of the bondholders. All expenses incurred in carrying out the provisions of the trust agreement or resolution may be treated as a part of the cost of the operation of the airports.
D.C. Code § 9-916