Seems they have some experience flying three-engined 747s:
http://www.airliners.net/open.file/224038/L
BTW: Read the caption; this one was intentional, although it does say a crack in the no.3 engine mount was found in HNL. I guess the same happened here, only they didn't find out before they took off from ORD.
Still, good riddens it happened on their way to JFK and not during the next leg over the Atlantic
