$flight_id = filter_input(INPUT_GET, "flight_id", FILTER_SANITIZE_STRING);
$class_name = filter_input(INPUT_GET, "class_name", FILTER_SANITIZE_STRING);
$client_id = get_client_id($_SESSION['email']);
$flight_id = filter_input(INPUT_GET, "flight_id", FILTER_SANITIZE_STRING);
$class_name = filter_input(INPUT_GET, "class_name", FILTER_SANITIZE_STRING);
$client_id = get_client_id($_SESSION['email']);