BLEEP BLOOP: I just saw an aircraft with callsign #DAL2121 (ICAO code #A03B6D) flying at 311 kt at altitude 8900 feet MSL at coordinates 34.2385,-118.4393.

That's, like, super fast.

https://globe.adsbexchange.com/?icao=a03b6d
https://www.openstreetmap.org/?mlat=34.2385&mlon=-118.4393#map=15/34.2385/-118.4393

BLEEP BLOOP: I just saw an aircraft with callsign #DAL2121 (ICAO code #A03B6D) flying at 315 kt at altitude 8900 feet MSL at coordinates 34.2927,-118.5045.

They must have had a 50 knots tail wind.

https://globe.adsbexchange.com/?icao=a03b6d
https://www.openstreetmap.org/?mlat=34.2927&mlon=-118.5045#map=15/34.2927/-118.5045