将变量从控制器发送到503页面

Question

I'm developing with Symfony2, I want to send the variable myDate to my custom page 503 (error503.html.twig).

{# error503.html.twig #}

{% if myDate is not null or myDate is not empty %}
    Start date : {{ myDate }}
{% else %}
 {{ render(controller('MyBundle:myController:index')) }}
{% endif %}

When the service is not available, the page 503 is displayed, but the variables are not sent to this page from the controller. I tried with the render template and it does not work (no error, just no variable that appears).

/** myController.php **/

public function indexAction()
{
...
 return $this->render('TwigBundle:views:Exception:error503.html.twig', array(
        'myDate' => $startDate, 
     )); 
...
}

I specify that it works with 403, 404 ... but not with the 503 exception . Thanks for your help.