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

🇬🇧 G-YMMK - Boeing 777 236ER - British Airways BAW91C/BA91C, London Heathrow (LHR) to Austin-Bergstrom (AUS) - 5.1 mi away @ 40375 ft, heading SSW at 538 mph. Spotted once before! [01:58:54 PM CDT] #4007F6 #G_YMMK #B772 #SPEEDBIRD #BAW91C #BA91C #ADSB #ADSBbot