Two too many?

With each progression civil aviation took a bold new step and gradually the culture of the travelling public caught up and kept pace. Dinner jackets and silver service slowly gave way to the cold efficiency of international air travel where time was of the essence. In two decades the face and very nature of world travel had changed, but still there remained one constant; four engines.

For all intents and purposes, once an airliner sought to reach far beyond its borders, only four engines would suffice. Those engines could be pistonpowered or turbojet, but either way there needed to be a quartet of them once land lay behind and oceans lay ahead. Pilots and passengers alike clung to the comfort of seeing multiple power units sitting outside their windows – a wealth of ‘spares’ ready to carry on should one or two fail, regardless of the reality of the performance implications.

From the Boeing 707 and the DC-8, to the emergence of the game-changing ‘Jumbo Jet’ there was safety in numbers and the ‘light twins’ were better served staying closer to home. Even so, change was afoot and as surely as designers ultimately proved that biplanes could fly without a top wing, the extinction of outboard engines fell under their slide-rule’s steely gaze.

The transition to two-engined global airliners was not a giant leap in logic. Fuel prices were on the rise and engine technology had evolved dramatically. Tremendous new high-bypass engines could deliver levels of power and reliability that could only once have been imagined. Now their documented performance was beyond argument.

The leap of faith was somewhat more difficult to achieve. To one and all, two engines did not seem quite enough to span the world. After all, it only provided a lone spare engine should one have cause to fail. It was a compelling argument and one that the greater travelling public could understand far better than the incredible dispatch reliability and workings within the modern jet engine. Consequently, the move to twin-engined fleets was more about a change in perception and culture than it ever was about performance.

The first tentative steps were taken to allow the twin jets to fly increasingly further from the safety of alternate airfields. Extended Twin Engine Operations, or ETOPS, gradually edged the aircraft farther from land as their track record of reliability began to bank up in undeniable statistics. In the early days pilots could still be heard to err that “It’s a long way on only two engines” or that ETOPS stood for, “Engines Turning Or Passengers Swimming”. In time these jests and their supporting arguments began to fade in the wake of aircraft like the Boeing 777. Its impeccable safety record led to a bloodline that continues to grow today in its latest gestation, the 777X. Even its smallest sibling, the Boeing 737 began to stretch its wings and fly farther from home than it had ever done before. Just as the monoplane said goodbye to the struts, ETOPS was no longer an experiment, it was the norm.

Reliability had become the expectation of passengers and the majority no longer counted the engine cowlings outside their window as they fastened their seatbelts. Now the inflight entertainment system and cabin service had a greater impact on their travel decisions. It was a change that was not lost on the airlines and manufacturers.

And what of the four-engined giants? While Airbus launched its massive A380 and Boeing sought to build upon the long-held superiority of the 747 with new variants, it has been the Boeing 787 and Airbus A350 ‘twins’ that have heralded in the new century with their bulging order books from expectant airlines. The four-engined ‘heavies’ with efficient engines have their niche in the market, but will they always? That niche is no longer established on the back of four-engined security, it emanates from the ability to uplift massive payloads and minimise airspace ‘slots’. As such, the airlines may well determine the ultimate fate of these giants with their future policies. Service frequency may become the priority and the economics of fuel purchasing will continue to weigh heavily on fleet decisions.

It is possible that there will come a time when all air travel is conducted by twin-engined airliners. The cultural acceptance will be complete at that point and four engines will be a novelty. ETOPS and Extended Range (EROPS) will still have their specific operational requirements to satisfy, but will essentially be the norm.

Today we look back at the flying boats nostalgically as the ladies of the skies whose time at the top of the tree was a fleeting glance. Progress maintained a heady pace throughout the twentieth century to bring us to this point today. What will come next? Will pulse jets skip airframes off the atmosphere to have us in London by lunch? And if they do, how then will we perceive the graceful four-engined giants? Perhaps we will warm at the sight of their sheer expanse, or perhaps we will reflect upon the days when four engines was really two too many.