To travel from Los Angeles International Airport (LAX) to downtown Los Angeles, it is most convenient to use the Flyaway bus. The Flyaway bus stops are located outside the airport's arrival terminals.

Exit signs for Flyaway bus from arrival terminal.

Wait for the Flyaway bus under these signs.

Flyaway buses have several different destinations. Take the Flyaway bus for "Union Station."

Payments for the bus are made upon arrival at Union Station. Pay at the Flyaway kiosk located near the bus stop at Union Station. Cost of one-way trip is $7.

Pay at the kiosk on the left.

Flyaway kiosk.

Cash is NOT ACCEPTED. Credit cards such as American Express, Discover, Mastercard, and Visa are accepted as well as debit cards. However, the Metrolink ticket machine accepts cash to purchase Flyaway tickets. Also, Flyaway tickets may be purchased online. Use the link below to purchase an online ticket.

Upon paying for Flyaway bus at the kiosk, show the receipt to the bus driver to receive checked-in luggage.
From the Flyaway bus stop, proceed to Union Station.

The entrance for Union Station is located at the stairs near the pole to the left.

The entrance to Union Station is located towards the left at the bottom of the stairs. Walk straight ahead from the entrance, and reach the passageway that leads above the station's platforms. Head for the platform of "Metro Gold Line." Next to the stairs leading up to the platform, there is a ticket machine to purchase a TAP card. Purchase a TAP card here. Because individual ride tickets are not sold, you must purchase a TAP card ($1) and add monetary values to it. Given that a single ride costs $1.50, you must pay at least $2.50 for the initial ride. Both cash and credit cards are accepted.

If you do not own a TAP card, select "Purchase new TAP Card + Fare," and pay at least $2.50.

Place the TAP card at the designated place on the machine at the ticket stall and enter the platform. For the Metro Gold Line, there is the train for Atlantic (heading towards East LA) and a train for Sierra Madre Villa (towards Pasadena). To head for Mission Headquarters, take the train destined for Atlantic. Exit the train at Soto Station (fourth stop). Take the escalators up, and upon exiting the station, take another set of escalator to the ground floor. You will arrive at the intersection of Soto Street and First Street. Cross the street and walk along First Street for ten minutes to arrive at the Mission Headquarters.

Soto Station is located to the left.
Head to the right along First Street to arrive at the Mission Headquarters.

Reference: Flyaway page on LAX official website.