Override meta query

snippet.php

<?php
// META QUERY
function searchExcludeOldMatches( $query ) {
    if (!is_admin() && $query->is_search) {

        $query->set('meta_query', array(
            array(
                'key'	  	=> 'ctl_visibility',
                'value'	  	=> 'true',
                'compare' 	=> '=',
                'type_key'  => 'CHAR'
            ),
        ));

        return $query;
    } else {
        return $query;
    }
}
add_filter('pre_get_posts','searchExcludeOldMatches');