A Long Stretch
A design that works sticks around.
The problem appears when a design is increasingly obsoleted by the boundary conditions but, still, it lingers more than what common sense would deem reasonable, mainly because the perceived effort to start a clean-sheet design is prohibitively higher than hacking a bit more the existing one. Until, of course, reality explodes in everyone's face, like those cigars in cartoons.
Everybody is shittalking Boeing these days. I am not going to delve into flying doors, loose bolts or quality control issues; I will leave that to all the knowledgeable armchair experts that are flooding our feeds with articles about the “downfall of Boeing”. Personally, I do not think Boeing is going down anytime soon, but they surely have homework to do if they want to fix their engineering and their credibility; I bet the stupidity that has encircled the engineering practice lately has reached them, as it has reached many other engineering firms of all sizes and colors across the globe. Boeing has it more difficult because the criticality level of the things they make is incredibly higher compared to other engineering firms who have also let their engineering rot in favor of consultants and vapid practices but run with the advantage that their failures don’t make headlines.
More than flying doors and falling oxygen masks, I am more into understanding how and why designs stick for unnecessarily too long.
The Boeing 737, one of the most iconic and widely used jetliners in the world, has a design history that spans over half a century. From its inception in the 1960s to the present day, the Boeing 737 has seen numerous iterations, upgrades, and redesigns, reflecting the evolving needs of the aviation industry but also perfectly illustrating the reluctance of organizations to let go of a market winner.
The story of the Boeing 737 begins in the 1960s. Boeing, looking to expand its product line beyond the large 707 and 727 models, designed the 737 as a smaller, more efficient short-haul airliner. The first model, the 737-100, made its inaugural flight in April 1967 (!). It was soon followed by the 737-200, which featured a longer fuselage and improved aerodynamics. These early models set the stage for what would become a highly versatile and long-lasting family of aircraft.
In the 1980s, Boeing introduced the 737 Classic series, including the -300, -400, and -500 models. These versions boasted advancements such as improved engines and greater passenger capacity. The Classic series solidified the 737's reputation as a reliable workhorse in both commercial and military aviation. “Workhorse” tends to be an euphemism for “a thing that pays the bills consistently so we better not touch it nor breathe too loud next to it”.
You could already feel the redesign fever derangement was unlocking when the 737 started to have those engines with weird flat bottoms.
When Boeing decided to update the 737 with more fuel-efficient, higher-thrust engines in the 1980s, they faced a technical challenge. The new engines, the CFM56 turbofans, were larger in diameter than the original Pratt & Whitney JT8D engines used in the first 737s. Thus, the Boeing 737 started featuring flat-bottomed engines to keep the landing gear the same and maintain adequate ground clearance. This distinctive design, often referred to as the "hamster pouch," allowed the engines to be mounted closer to the wing, thus maintaining the required clearance without major changes to the aircraft's design. You gotta love when a hack becomes a “distinctive” design feature. I bet someone patented something out of this.
The next significant leap came in the 1990s with the introduction of the 737 Next Generation (NG) series. This series included the -600, -700, -800, and -900 models, each offering various improvements like upgraded avionics, more efficient engines, and increased range. The NG series was a commercial success, becoming a mainstay for airlines around the world. Another red flag: when something is called “Next Generation”, you better start asking questions.
The most recent chapter in the 737's history is the problematic 737 MAX series, introduced in the 2010s. The MAX series, including the MAX 7, MAX 8, MAX 9, and MAX 10, was designed to be even more fuel-efficient and environmentally friendly, featuring new engines and aerodynamic enhancements. However, the MAX series faced significant challenges. Two fatal crashes involving the 737 MAX 8 model, in 2018 and 2019, led to a worldwide grounding of the fleet. The tragedies highlighted issues with the aircraft's flight control software and prompted extensive investigations, modifications, and a rigorous recertification process.
Now, if we compare the latest 737 MAX and the 737-100 from the late sixties. Are they the same thing?
Here, we can maybe discuss what “same” means when we talk about inanimate objects.
"The Ship of Theseus" is a philosophical paradox that explores the nature of identity and change. It centers around a legendary ship owned by Theseus, the mythical king and founder-hero of Athens. As the story goes, the Ship of Theseus was preserved in a harbor as a historical artifact. Over time, its wooden parts began to rot and were replaced with identical materials. Eventually, every part of the ship was replaced, leading to a compelling question: is the restored ship still the same Ship of Theseus? Furthermore, if the removed original parts were reassembled into a ship, which, if either, is the true Ship of Theseus? This paradox raises fundamental questions about what it means for an object to remain essentially the same despite changes and renewals.
Boeing's strategy in redesigning the 737 over the years reflects more of a calculated approach to stretch an existing system to achieve a multi-factor goal: build on top of a winning product with undeniable market share, but also saving the significant hassle with certifications compared to developing an entirely new aircraft. This approach was largely driven by economic and competitive factors, as well as the desire to meet the evolving needs of airlines without incurring the significant costs and risks associated with a new program which could cost billions.
By building upon the proven design of the original 737, Boeing was able to introduce new features, technologies, and improvements while maintaining a design “continuity”. This approach allowed Boeing to utilize many of the same parts, manufacturing processes, and even pilot training protocols from one generation of the 737 to the next, thus reducing the time and cost associated with bringing these new models to market. This not only permitted for a smoother certification process with aviation authorities, as the aircraft was already familiar, but also appealed to airlines, which could integrate these new models into their fleets with minimal additional training and without the need for extensive new support infrastructure.
You can really see how this could in fact make sense; if only we humans could see that invisible line between “enough” and “too much” and the inescapable nature of diminishing returns.
Boeing, and many others, went beyond this line; the Theseus’ limit. The 737 MAX crossed the line when Boeing took another stretch but this time the dynamic behavior of the aircraft was so altered that, just like Theseus’ ship, the thing silently became something else. Then, they expected a hack like the infamous Maneuvering Characteristics Augmentation System (MCAS) would make it behave like a 737 when it was already not a 737 anymore, costing 346 lives in the process. Sure, with the level of stakes at play, the 737 MAX can—and will—be made safe somehow, despite the Greek mythology. Thank you for flying with us.
No design lasts forever. By piling up incremental improvements we only approach faster to the point where the thing is not the same thing anymore, but something else. The clever ones start a new design *before* the previous one reaches obsolescence1.
To add some defense on Boeing, it is a rather known fact that Boeing was all but told by their customers—airlines—that if they pursued a clean sheet 737 replacement, they were switching to Airbus. Airlines are ruthless about the lowest cost option, and there’s no aircraft Boeing can build today—much less a decade ago—that can do the 737’s job cheap enough to overcome the massive logistical costs of transitioning pilots, maintenance, and support functions.
Updating the 737 was the smart business decision, QC problems, and the MCAS debacle notwithstanding. The latter wouldn’t have happened had certain airlines not pushed for MCAS to be omitted from publications, since that would have triggered a type rating change airlines weren’t about to swallow.