S&P Global Ratings has assigned preliminary ratings to five of the six classes of prime residential mortgage-backed securities being marketed on behalf of Toowoomba's Heritage Bank.  This transaction is the A$500 million HBS Trust 2017-1, a securitisation of prime residential mortgages originated by Heritage Bank. "The rating reflects our view of the credit risk of the underlying collateral portfolio, including the fact that this is a closed portfolio, which means that no further loans will be assigned to the trust after the closing date," S&P said in a pre-sale note. The top rated classes of A1, A2 and AB Notes, totalling $460 million, $15.0 million and $12,750,000 respectively, were all rated AAA (sf). Fitch Ratings also assigned its top rating, AAA (EXP) (sf) but did not rate any other lower rated tranches. "At the cut-off date of 14 September 2017, the total collateral pool consisted of 2,248 obligors, totalling A$500 million," Fitch said in a presale note.Pool Characteristics: The weighted-average seasoning of the portfolio is 53.3 months, with a WA unindexed loan/value ratio of 61.7 per cent and WA Indexed LVR of 56.6 per cent. The average obligor current loan size is A$223; investment loans represent 18 per cent of the pool by balance. The entire pool benefits from lenders' mortgage insurance.