Simbad, tulips.
When Court line started operating Tristars (-1) Luton-Antigua (1972-3) the UK overwater rules related to 50% of the power plants inoperatives based on 4 engined aircraft.(Hence the twins only relate to single failure) This was the first time that 3 engined aircraft had been involved in this long range flying so the CAA stated that the performance was predicated on 2 engines inop. The Luton - Santa Maria leg was not a problem as at the overwater stage the aircraft was light enought to maintain on 1 engine. The Santa Maria-Antigua leg was more of a problem due to high weights for the southbound leg. With the aircraft at MTOW the CAA allowed that any point during the climb a double engine failure would allow the aircraft to descend on its climb path thereby allowing it to get back to Santa Maria. After TOC double engine failure would result in drift-down. After the failure(s) the aircraft starts going down hill at an fixed rate but as fuel is burnt off that rate decreases. The original Lockheed drift down figures recomputed the drift down rate every 2,000 feet and this did not allow the operation. Lockheed went back and re-computed the drift down at every 100 feet which then made it work !!
Court Line operated the route until its demise in 1974.