And certainly, even as turbofan and aircraft manufacturers alike make appeals to cleaner technology, their goal is not to reduce human air travel. Regarding its A330 model, Airbus charts 1,694 orders for these planes, of which only 1,373 are fulfilled. The implicit message: Demand has not been met, which means building more planes, and faster. And this is presented as an ongoing condition. An airline manufacturer would never aim to satisfy the needs of all airlines once and for all, but rather to keep producing new jets ad infinitum. So even if the planes to come are powered by relatively cleaner Trent 7000 turbofans, the assumption—the goal—is to put ever more A330s in the sky. That somewhat complicates the straightforward aim of hitting “environmental targets,” as Rolls-Royce puts it. Individually, sure—but collectively, if more planes are in the sky?

Aviation futurists might argue that as old planes are retired, the newer, more efficient aircraft will simply replace these, and that consolidation will reduce overall flights and eliminate unnecessary routes. Yet it is clear that Airbus and Boeing are hardly going to turn away new business, or slow down production. Consider how Airbus boldly claims that their A320 family is the “world’s best-selling aircraft of all time”; and then look at how Boeing shows off their cornucopia of customers for their comparable next-generation 737. This is obviously a race for growth, not just efficiency.

Turbofan engines offer an audible reminder of the paradox of progress. As much as people may want to experience new things, they have to use old tools and means to do so. Sometimes those tools and means can function as blinders. People are tied to existing patterns, infrastructure, and systems even as they might want or need to do something different and truly innovative.

Leaving Washington a few days later, I was struck by the beauty of Eero Saarinen’s Dulles International Airport at dawn. The way it sweeps up from the ground, how it architecturally announces the grand project of flight. It feels like a paean to the jet age, a living monument of sorts.

As I plodded through the security-checkpoint slog to my gate, however, it occurred to me how stuck travelers are in this bizarre moment of the past, this mid-20th-century endeavor that is jet travel. Innovations in turbofan-engine design and technology may be well-intentioned and forward-thinking, at least in some sense. And the actual work that turbofans do day in and day out, hour after hour of nonstop chugging across the sky—it’s nothing less than incredible, from a technical standpoint. But, at the same time, the din of flight really can’t help but remind people of something that had its heyday several decades ago.

The bitter truth is that human air travel probably won’t get much better in the years to come. It might have reached certain limits in terms of speed, economy, and comfort. There are any number of signs that this is the case: climate change, limited resources, land-use constraints, wealth inequality, and so on. Recently, news broke about problems in the Rolls-Royce Trent 1000 engines that power the Boeing 787, which was first introduced in 2011: The turbine blades on two separate aircraft broke down during flight, resulting in severe vibrations and causing the aircraft to abort their journeys. Concerning these recent incidents, Warren East, the chief executive at Rolls-Royce, admitted an obvious but uncomfortable truth about turbofan parts: “They wear out.”