turn backs are required by the company. If for instance you departed on a 3 hour sector overflying numerous airports we would have continued on most days with an engine failure however I am told that did not sit well with CASA and so a note was made in our manuals " if an engine fails, or is required to be shutdown during climb, the primary consideration should be to return to the departure airport. The only exceptions to this policy would be weather precluding a return or a suitable airport being available within close proximity." On a seperate note the aircraft will easily fly a long sector on 3 engines however within the last 3 hours there needs to be a heap of airports available to meet your needs on two engines if a susequent engine fails and that is where you can find yourself in between nowhere and no where. Fine in practise returning to europe or asia overland but on a pacific route. no way withour rerouting and the plan and fuel carried would not allow this.