How to join multiple columns from different tables
Try this one, use INNER JOIN from booking to aircraft_model

SELECT
    b.booking_id,
    c.firstname AS First_Name,
    c.last_name AS Last_Name,
    am.aircraft_model
FROM booking b
INNER JOIN customer c ON b.customer_id = c.customer_id
INNER JOIN aircraft a ON b.aircraft_id = a.aircraft_model_id
INNER JOIN aircraft_model am ON a.aircraft_model_id = am.aircraft_model_id