L-1011
By far the best airplane I ever flew. Way ahead of it's time.
My understanding is that the RR RB.211 engine did not live up to it'e specifications. It used more fuel and required earlier overhauls than the sales people said it would. This translated into higher operating costs for the airlines.
Too bad, for it was such a beautiful bird. With the DLC (direct lift control) the approach and landing were so easy.
Unfortunately Lockheed got rid of the moulds and refused to allow other manufacturers to copy the DLC system.
As for the SO vs FE question, the SO was a pilot (P3) and the FE was a mechanic (no pilot licence). Different airlines used one or the other.
I didn't know the L1011 was still being used by airlines, thought they were all gone to bed.