[dingaling]

The DC-10 was a rushed programme to avoid Douglas being frozen out of the 1970s widebody market by Lockheed and Boeing.

Similarly, the MD-11 was a cost-restricted update of the airframe to avoid McD being frozen out of the 1990s widebody market by Airbus and Boeing.

McD management wouldn't fund the more ambitious four-engined MD-12, so the trijet's fuselage was stretched and aerodynamic tweaks applied.

The MD-11 never met its performance targets and heralded the end of the Douglas commercial line. It was fairly quickly relegated from pax to cargo service where it has a good payload but little else to commend it.

[consumer451]

I always thought that the third engine was thrown into the tail of the DC-10 when they learned of the L-1011. However, I think I first heard that from a retired Tristar pilot.

https://en.wikipedia.org/wiki/Lockheed_L-1011_TriStar

[dghlsakjg]

Trijets were mostly a thing to allow operations further away from diversion airports. Until the mid 80s twin engine jets had to stay less than an hour from diversion airports which meant that most stuff over water or remote routes had to be trijet or quad.

The MD-11 was late to that party, and by the time they started flying they were already allowing twins to go farther. Now the limit is all the way up to 370 minutes from the nearest airport for some twins, and most are capable of flying transatlantic.

[consumer451]

My personal theories as far the current grounding of all MD-11s:

1. Boeing wants no more responsibility for these airframes. Good call by the Board.

2. MD-11 style engine arrangement is an entire design flaw in itself. You can only recover from an uncontained engine failure at V1 if two engines remain. Good luck with that since on the MD-11, engine #2's intake is in the debris field of the other two turbines.