preliminary rating opinion letter from at least 1 rating agency, indicating that the senior obligations of the eligible infrastructure project, which may be the Federal credit instrument, have the potential to achieve an investment-grade rating. (2) Rural infrastructure projects With respect to a rural infrastructure project, a rating agency opinion letter described in paragraph (1) shall not be required, except that the loan or loan guarantee shall receive an internal rating score, using methods similar to the rating agencies generated by IFA, measuring the proposed direct loan or loan guarantee against comparable direct loans or loan guarantees of similar credit quality in a similar sector. (h) Investment-Grade rating requirement (1) Loans and loan guarantees The execution of a direct loan or loan guarantee under this Act shall be contingent on the senior obligations of the eligible infrastructure project receiving an investment-grade rating. (2) Rating of IFA overall portfolio The average rating of the overall portfolio of IFA shall be not less than investment grade after 5 years of operation. (i) Terms and Repayment of direct loans (1) Schedule The Chief Executive Officer shall establish a repayment schedule for each direct loan under this Act, based on the projected cash flow from eligible infrastructure project revenues and other repayment sources. (2) Commencement Scheduled loan repayments of principal or interest on a direct loan under this Act shall commence not later than 5 years after the date of substantial completion of the eligible infrastructure project, as determined by the Chief Executive Officer of IFA. (3) Deferred payments of direct loans (A) Authorization If, at any time after the date of substantial completion of an eligible infrastructure project assisted under this Act, the eligible infrastructure project is unable to generate sufficient revenues to pay the scheduled loan repayments of principal and interest on the direct loan under this Act, the Chief Executive Officer may allow the