I posted this as a response to a topic but is also here under it's own steam. A tri-jet is less powerful and has a lesser max climb performance than a twin. To be certified for operation, a new plane must be able to climb with one engine out. So a 757 must be able to climb with half of it's power lost, whereas an MD11, TriStar or 727 must be able to climb with only a third of it's power lost (not sure of exact rule on 4 engine designs).Therefore, the power in reserve on a twin is correspondingly higher, and a twin at max power would be able to outclimb any trijet, let alone any 4-engine design. This is why in some circles (the author included), twins are safer than 3- and 4-engine designs because most accidents occur on take-off and landing, virtually never over the ocean and never ever because of mechanical problems with engines (since jets). The greater power-to-weight ratio in a twin gives an extra margin of power when it may be most needed.
fly Saha Air 707s daily from Tehran's downtown Mehrabad to Mashhad, Kish Island and Ahwaz