Engine failure
2 Engines = 100% power available = 50% BACK-UP AVAILABLE WHEN 1 ENGINE FAILS
1 Engine = 50% POWER LEFT = 0% BACK-UP AVAILABLE WHEN THE REMAINING ENGINE FAILS
4 Engines = 100% power available =75% back-up when 1 engine fails
3 engines = 75% power available =50% back up when 2 ,, ,
2 engines = 50% power available =25% back-up etc
This tells me that any in-flight departure from full power availability to something less behoves one to land at the closest opportunity. Are there places on this globe where one is 5000 km away from a "closest" opportunity to land ? Is it possible that commercial flights are increasingly venturing over areas (North pole, longer tracks over water) where "closest" opportunity is compromised ? Responsibility for many lives (say a fully loaded A380) has to take precedence over expediency.............which has the potential to lead to snowballing problems.