I hate to have a go at Danny, but as someone who was awarded an Astro Nav Certificate and a Bridge Watchkeeping Officer's Certificate whilst in the Royal Navy I am well aware of the curved nature of the earth. I have in fact flown with BA from LAX to LHR when I did my PPL in California, so I am well aware of the likely route. I also have a fATPL and a very good mark in Gen Nav.
Just because the original flight plan was probably a route well away from the likes of Boston or New York is there anything to prevent the Captain choosing to make such a city the destination? He after all the Captain and has ultimate responsibility for decision making. Or thats what they taught me when I did air law. Maybe different when on the line these days though.
Let us also consider if the engine had failed 60 seconds or so earlier ie before V1. If it had done the take off will have been abandoned, aircraft to hangar, crew & pax to hotel. But because they got 100ft of the ground before the failure they can continue 5000nm to London. And that is legal and safe, if it seems on the face of it a little odd. As they say 'the law is an ass'.
There is no way you can determine in my opinion, other then by visual inspection on the ground, as to whether or not an engine failure is contained or uncontained. Somebody posted earlier the EGT was 120 degrees above the max limit of 1080. The engine had to be completely shut down to bring the EGT back in limits. No way of telling that some piece of Rolls Royce's finest has not been spat out and damaged the underside of the leading edges, the flaps, maybe hit an elevator or rudder, or perhaps punctured the underside of the fuselage at some point. Was anything like this considered? Or was it assumed all was ok in regard to this as no such indication received by the time the finished circling off the coast?
Seems to me that the whole decision was based entirely on did they have enough fuel and enough performance to get back to the UK on three engines. To my mind there were other things that needed to be considered before considering a 5000nm, 10 hour trip back home following an engine failure at take off.
My MCC instructor was an ex BA 744 Captain. He did say it was not uncommon for 747's to continue to destination OEI. But I am not sure he said it was normal to do so if the failure occured 100ft above the ground following take off.
My greatest concern is that 'pilots' and 'aviating factors alone' are no longer the sole individuals involved in deciding what to do following a malfunction. What is known as 'good airmanship' seems ever more to lag behind economics, passenger convenience, environmental concerns and what you could losely describe as 'making the rules work for you'.