TRUST INDENTURE.

(a) Authority bonds, including refunding bonds, that are not payable wholly from ad valorem taxes may be additionally secured by a trust indenture. The trustee may be a bank with trust powers located inside or outside this state.

(b) A trust indenture, regardless of the existence of a deed of trust or mortgage lien on property, may:

(1) provide for the security of the bonds and the preservation of the trust estate as prescribed by the board;

(2) provide for amendment or modification of the trust indenture;

(3) provide for the issuance of bonds to replace lost or mutilated bonds;

(4) condition the right to spend authority money or sell authority property on the approval of a licensed engineer selected as provided by the trust indenture; and

(5) provide for the investment of authority money.