🇺🇸 N37551 - Boeing 737MAX 9 - United Airlines UAL1338/UA1338, Washington Dulles (IAD) to San Francisco (SFO) - 4.4 mi away @ 31500 ft, heading W at 519 mph. Spotted 10x before. [07:36:30 PM CDT] #A4497F #N37551 #B39M #UNITED #UAL1338 #UA1338 #ADSB #ADSBbot