> Yeah my understanding is that the 747 was a success because it could cross the major oceans in a single go, something smaller twin engines could not do at the time.
Technically they could but regulations didn't allow it at the time: 1953 FAA regulations required that twin-engined aircrafts always be within 60mn of an airport, and ICAO had slightly less restrictive limits of 90mn. This meant some routes were entirely unfeasible, or the flight path required to keep within 60~90mn of an airport at all time made it uneconomically unfeasible.
3- and 4-engined aircrafts were not affected by these rules (starting in '64 for the 3-engined ones).
The rules started being relaxed in the mid-80s with the introduction of ETOPS ratings (initially 120 and 180, now up to 370).
