Map of the St. Louis area showing the position and track of the aircraft described in the post.

🇺🇸 N12221 - Boeing 737NG 824/W - United Airlines UAL2255/UA2255, Denver (DEN) to Indianapolis (IND) - 4.5 mi away @ 37250 ft, heading E at 560 mph. Spotted 15x before! [01:06:39 PM CDT] #A05DD8 #N12221 #B738 #UNITED #UAL2255 #UA2255 #ADSB #ADSBbot