Wirelessly posted (iPhone 4: Mozilla/5.0 (iPad; CPU OS 5_1_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9B206 Safari/7534.48.3)
Each pilot is clocked to do 8 hours only, and even the plane is on auto pilot it doesn't mean the plane does not need 2 pilot to sit there in case if there is anything happening.
For long sector like YYZ that is 15 hour I don't think there's lots of margin for error.