OK I know that an Swm is a metroliner, a DH8 is a Dash 8 and a 743 is a B747 - 300 series, but what is an ER4? I see that I have to fly on one operated bt American Eagle from DFW to CHS. The seat map shows that it has an A seat for 18 rows, an aisle and B and C seats for 18 rows. Can someone...