I had no idea that Trijets were effectively limited by a form of ETOPs limitations at all!
Not sure about anyone else, but in the good old days before 9-11, when flight deck visits were not a problem, I was on a longhaul DC-10 from LGW to DFW heading for a flight simulation conference, and we ended up routing a long way north over Greenland. There were a couple of us visiting at the time, and we got talking about some of the restrictions on the 10. At that point, one of the more dusty manuals came out, and the FE and ourselves retreated to the front galley area to look at the book in some detail, and allow the cabin crew to rotate some younger visitors into the flight deck.
The relevant section got found, and it transpires that there's a limit on the DC-10 that it can't go above ( I think, it was a good while back now) 70 or 75 N, as in the event of a pressurisation failure, it can't get clear of the FL170 sector safe altitude limitation before the oxygen generators expire, and if they've no pressurisation and no oxygen, they need to get down to FL120 or less. I have to admit, that little nugget gave us some pause for thought when we sat down to think about it in some detail.
Suffice to say that the conversation on the flight deck was sufficiently stimulating to all concerned that we were still there enjoying the view, ( it was a rare VFR day) and the conversation as we passed over the home of Flight Simulation, Chicago Meigs, some good while later.