Zeke,
"Flight on 3 engines is not unairworthy, the 747 is actually FAA approved for takeoff and flight on 3 engines, "
Are we not being a little bit cute here? I presume you are referring to a three engine ferry. The fare paying public would not be on board.
In fact, at my company, by contract, the line pilot is not required to do three engine ferries. Those are done by management pilots.