(a) FHA-Insured projects. (1) The debt service reserve shall be invested and the income used to pay principal and interest on that portion of the obligations which is attributable to the funding of the debt service reserve. Any excess investment income shall be added to the debt service reserve. In the event such investment income is insufficient, surplus cash or residual receipts, to the extent approved by the field office, may be used to pay such principal and interest costs.

(2) The debt service reserve and its investment income shall be available only for the purpose of paying principal or interest on the obligations. The use of the debt service reserve for this purpose shall not be a cure for any failure by the owner to make required payments.

(3) Upon full payment of the principal and interest on the obligations (including that portion of the obligations attributable to the funding of the debt service reserve), any funds remaining in the debt service reserve shall be remitted to HUD.

(b) Non-FHA-insured projects. (1) Investment income from the debt service reserve, up to the amount required for debt service on the bonds attributable to the debt service reserve, shall be credited toward the owner's debt service payment. Any excess investment income shall be added to and become part of the debt service reserve.

(2) The debt service reserve and investment income thereon shall be available only for the purpose of paying principal or interest on the obligations. The use of the debt service reserve for this purpose shall not be a cure for any failure by the owner to make required payments.

(3) Upon full payment of the principal and interest on the obligations (including that portion of the obligations attributable to the funding of the debt service reserve), any funds remaining in the debt service reserve shall be remitted to HUD.