// first two
$year = substr($flightDates->departureDate->year,2);
// last two
$year = substr($flightDates->departureDate->year,-2);

但是考虑到你在这里解析一个日期,使用date函数会更加智慧.
体育strtotime()和date()或甚至：

<?PHP
$someDate ='200912';
$dateObj = DateTime::createFromFormat('dmy',$someDate);
echo $dateObj->format('Y');
// prints "2012" .. (see date formats)