$re = '/\b[0-9]{1,2}\s+\S+\s+[0-9]{4}\b/';
$str = 'Votre vol : Casablanca - Paris Mercredi 31 août 2016 AF1197 - Ecoi 7 septembre 2016';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php