Thanks John,
For anyone else that may be interested, I also had to move the echo outside the loop. Working code below.
<?php
$posts = get_posts(array(
'posts_per_page' => -1,
'post_type' => 'pov_travel'
));
if( $posts ):;
$dla = 0;
foreach( $posts as $post ):
$dla += get_field ('dla');
endforeach;
echo $dla;
endif;
?>
