Isn't the third engine on the MD-11 just for TO performance and to act as a spare in the cruise? :DBest regards,Robin.

No

In the days when DC-10s and L-1011 where designed, there weren't powerful enough engines to get safely those giants into the air with only two units.Furthermore, there only was an ETOPS-60 rule. Twins were not certified for crossing the Atlantic in commercial flights.So, McDonnell and Lockheed built the "Three-holers", that where, at least in their external aspect, "strangely" similar, don't you think...?Why didn't they go for a quad like Boeing with the 747 ?, even when the maintenance duties in the #2 engine were extremely complicated..Any aviation historian out there ??