Your best options are to take anyone of the Sunday late morning scheduled Metrolink trains from San Bernardino to LA Union Station and then take one of the Fly Away Buses to LAX to arrive ahead of time for your scheduled flight. "You would rather arrive too early then to arrive too late and miss your flight and connections." The Fly Away Buses runs every 30mins from LA Union Station to LAX. *Due to ongoing construction and service disruptions on the Blue Line and Green Line Metro Rails through the end of September 2019, this is your best sufficient option unless you have someone that will drive you directly there. Have a safe trip.
Take the San Bernardino route to LA Union Station and once there you can take the Red Line to the Blue Line and then finally the Green line to LAX. Seems long but they connect fast. Also there is a Fly Away Bus at LA Union station that would take you straight to LAX but times are limited.
Where San Bernardino Transit Center location
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