Sorting ComboBox in Flex 1.5

I am using a editable Combobox which is populated by serverside code.

 I want that when anybody type in combobox say "A" it will open and
show all 
records starts with "A".
 As the user types words("AI") in combobox it will sort and show the
records 
starts with "AI".

 How we can achieve this?

 Thanks in advance!

 Vinay