In the decades following their introduction, their use has gradually declined due to a variety of factors, including the approval of twin-engine jets to fly farther from diversion airports as reliability increased, and an increased emphasis on fuel efficiency.

The shift away from 4-engine planes (like the Boeing 747 and Airbus A380) is driven by engine reliability, fuel efficiency, and changing regulations. Modern jet engines, such as the Rolls-Royce Trent XWB, are 25% more fuel-efficient than older models, allowing two engines to do the work that once required four. Economically, maintaining four engines is nearly double the cost in terms of inspections, parts, and labor. Furthermore, the introduction of ETOPS (Extended-range Twin-engine Operational Performance Standards) changed the legal landscape; previously, twin-engine planes were restricted from flying long distances over oceans for safety. As engine reliability reached near-perfection, these rules were relaxed, allowing twin-engine jets to fly almost anywhere on earth. Today, airlines prefer the "flexibility" of flying two smaller, efficient twin-jets on different schedules rather than trying to fill a single 500-seat "superjumbo," making the 4-engine giant a relic of a less efficient era of aviation.