convert double latin letters to US7ASCII
===

How can i convert **Æ**`(latin capital letter ae)` to **AE**`(US7ASCII)` in  oracle.I have tried with following query below:

    SELECT CONVERT ('Æ', 'US7ASCII') FROM DUAL;

But it gives me **?** as output ,but the same query is working for single characters as shown below:
    
    SELECT CONVERT ('à', 'US7ASCII') FROM DUAL;

    OUTPUT
    ==========
     a
    ==========

