National Australia Bank continued the trend towards longer terms on mortgage-backed securities issues this year in announcing yesterday that it had upsized its National RMBS Trust 2011-1 with three-year terms for the A1 and A2 tranches.NAB will pay 100 basis points over the one-month bank bill swap rate on the A$720 million A1 tranche, which is rated AAA and has a weighted average life of three years.It priced the $210 million A2 tranche, which also has a weighted average life of three years, at a fixed rate of six per cent. The A2 tranche is a soft bullet, which means there is no amortisation before the scheduled maturity. It is designed to look like a fixed interest security that can be included in the UBS Composite Bond index by conforming to fixed interest fund-manager mandates.Pricing on the B and C tranches was not disclosed. All up, NAB issued $1 billion of securities - up from the $750 million the bank announced last week.NAB's spokesperson, Elisha Vincent, declined to say how many investors bought the notes, what the mix of domestic and offshore investors was, or what the mix of balance sheet and real money investors was.Pricing was wider than Commonwealth Bank's Medallion issue in April, which priced its $2.2 billion A1 tranche at 95 basis points over swap. It was in line with the pricing of recent AMP and ME Bank deals.The three-year term of the A1 tranche was longer than any other issue this year and is almost double that of deals done late last year.