Hi i have been trying to add new product type to zencart and is succesfull half way. i cant seem to add new functions to general.php or as a new products_new_functions.php

following this help
blog.kineticpulse.co.uk/2010/11/creating-new-product-type-in-zen-cart.html

this is the function im trying to add
PHP Code:
  function zen_get_products_airline($product_id, $language_id) {
    global $db;
    $product = $db->Execute("select products_airline
                             from " . TABLE_PRODUCTS_DESCRIPTION . "
                             where products_id = '" . (int)$product_id . "'
                             and language_id = '" . (int)$language_id . "'");

    return $product->fields['products_airline'];
  } 
the moment i add a new fucntion in general.php or a new file in extra_functions.

the admin area shuts down.

only get black page;
<html>
<head></head>
<body></body>
</html>