Now that the quad-jets (namely the Airbus A340, Airbus A380, and Boeing 747) are out of production, they are slowly being replaced by twin-engine aircraft. So now, if an engine flames out, that means the aircraft loses 50% of its engines instead of 25%. There are no quad-engined airliners in production today (although, ironically enough, the introduction of ETOPS is credited with being one of the factors that killed the Airbus A380).