worksheet function - How do I set a column not to scroll till it encounters a value in Microsoft Excel?

I have a table like as attached (similar, but on a much bigger scale):

I want to set it up such that when I scroll down column B, cell A2 with the value "A" remains displayed at the top, until the cell A5 with the value "B" reaches the top. At that point, the top cell should be cell A5 with the value "B", till the scrolling proceeds to the value "C" (cell A10), and so on.

Is this possible?