A drop of NZ$100 million in break fees was one of the chief contributors to a 13 per cent fall in ASB Bank's cash net profit in the year ended June 2010.The bank - the New Zealand subsidiary of Commonwealth Bank - also blamed the drop on a decline in trading income, which together with break fees led to other banking income falling to NZ$342 million, down 33 per cent from the previous year. Trading income reduced as markets stabilised during the year.  Break fees related to customers breaking fixed rate mortgages decreased compared to the prior year and declined in the second half to more normal levels.Overall, the New Zealand business, which includes Sovereign and other small businesses, saw a 14 per cent fall in cash profit to NZ$461 million.ASB's net interest margin was stable at 1.6 per cent on continued high cost of funding and intense competition for retail deposits.Impairment provisions dropped sharply to NZ$125 million, down 47.5 per cent from the year before.  The bank had booked impairment provision of NZ$133 million in the nine-month period to March, which means it had a net reversal of NZ$8 million in the final quarter to June.However, asset quality showed a worsening trend in the last couple of months, as indicated by a rising trend in 90-day past due assets.