McDonnell Douglas MD-90 (N908DA)

the whole dc-9, MD series of twinjets has been by all measures an invaluable asset to the carriers smart enough to buy lots of them. American Airlines once had over 250 of this series, Delta had lots of them too. Douglas stretched them out step by step, but my favorite is the DC-9 shortie- just a fun rocketship to fly in. I see one every once in a while, but i remember St Louis airport with TWA having a few dozen on the field several times a day.