NW flies the DC-9-30 and ARJ between PHL and MEM. The -30 version of the DC-9 is annotated as D9S and has 100 seats. While you'd be fine on the DC-9, I think most of the folks here will tell you to select the ARJ......it is designed for 85 seats, but limited to 69 due to the NW pilot contract. A very popular aircraft with our FT'ers.

http://www.seatguru.com/northwest/ARJ.shtml

Stay off the CRJs......

Other variants of the DC-9 are the DC-9-10 (DC9, 78 seats), DC-9-40 (D94, 110 seats), and DC-9-50 (D95, 125 seats). There are about 8 -10s, 112 -30s, 12 -40s, and 35 -50s in the fleet, so most of your DC-9 flying will be on the -30 version.

Have a great trip to Melvis......