They do put extensive precautions in place for over water duel engine flights: https://en.wikipedia.org/wiki/ETOPS https://en.wikipedia.org/wiki/ETOPS “Avoidan

They do put extensive precautions in place for over water duel engine flights: https://en.wikipedia.org/wiki/ETOPS https://en.wikipedia.org/wiki/ETOPS “Avoidance of multiple similar systems maintenance. Maintenance practices for the multiple similar systems requirement were designed to eliminate the possibility of introducing problems into both systems of a dual installation (e.g., engines and fuel systems) that could ultimately result in failure of both systems. The basic philosophy is that two similar systems should not be maintained or repaired during the same maintenance visit. Some operators may find this difficult to implement because all maintenance must be done at their home base.” http://www.boeing.com/commercial/aeromagazine/aero_07/etops.html http://www.boeing.com/commercial/aeromagazine/aero_07/etops....