If Specific Row Contains A Word Then Clear Specific Content In Corresponding Column

I have a row (will always be row 3) where each cell contains a day of the week, the days repeats for a year or so, making the row almost 400 cells.

Like this,
Mo - Tu - We - Th - Fr - Sa - Su - Mo - Tu - We - Th - Fr - Sa - Su - and so on...

Though, A3 doesn't have to be "Mo" because the days in this case can change (A3 can start with "Tu"), hence I think I need a macro.

So if this row contains a weekend, "Sa or "Su" I want all the cells in the column beneath that which contains a specific value to be cleared.

Example, if "Sa" or "Su" has 3 values in the columns under them, all the values that contain "X" or "Y" has to be cleared.

Like this:
Rows (1,2,3...,)
1----
2----
3 Mo - Tu - We - Th - Fr - Sa - Su - .. and so on..
4 A --- B --- X --- Y --- X --- B --- Y
5 A --- B --- X --- Y --- X --- X --- X
6 A --- B --- X --- Y - --X --- Y --- C

After the macro it should be:

1----
2----
3 Mo - Tu - We - Th - Fr - Sa - Su
4 A --- B --- X --- Y --- X --- B ---
5 A --- B --- X --- Y --- X --- ---
6 A --- B --- X --- Y - --X --- --- C

Notice the two examples in the excel file.

Excelforum.xlsx‎