You can’t return $maskapai from the same variable. Try below. You may also need to adjust it depending on how you set up the field output.
<?php
// vars
$maskapai_list = get_field('maskapai');
// check
if( $maskapai_list ): ?>
<ul>
<?php foreach( $maskapai_list as $maskapai ): ?>
<li><?php echo $maskapai; ?></li>
<?php endforeach; ?>
</ul>
<?php endif; ?>
