Why does it take so long to develop a passenger aircraft? I was researching about the Boeing 737 MAX, and came across some information on a Business Insider page:


  But in the 2010s, Boeing tried to replicate the success of the 737NG with the 737 Max. But this time, it wasn't simply competing with Airbus; it was playing catch-up. Boeing began to discuss a successor for the 737 as early as 2006, looking at both putting new, more efficient engines on an existing 737 airframe, or starting from scratch with a brand new airframe. Boeing knew that Airbus was similarly exploring an A320 replacement, but both companies were still in early stages.It was still trying to decide in 2010, when Airbus launched the A320neo family (neo = new engine option). The jets used the original A319, A320, and A321 airframes, but used new engines that offered a 15-20% increase in fuel efficiency, consequently lowering operating costs and giving the planes longer ranges. Airbus has since released two longer-range variants of the neo family — the A321LR and A321XLR.


Then the article began talking about how it could take up to 10 years for Boeing to create the new aircraft, so instead of creating a completely new airplane, Boeing decided to just add bigger engines.

Now my question is, why does it take so long to develop a new passenger aircraft?
It's similar with military aircraft. In a mature field it becomes ever harder to create something that is clearly better than what we have already.

Since every new development costs so much, the consequences of failure are immense. Therefore, management will try to lower the risk of failure which again drives up development cost and time. It is a self-reinforcing spiral.

Add to that the fact that we now have only two major civil aircraft producers which both are heavily backed by their respective governments and are too big to fail. This creates political interference which makes major decisions even more complex and precludes bold, risky decisions. Only the most safe* option will be chosen after years and years of deliberations.

And I refuse to believe that we don't know enough yet in aerodynamics or materials science. When a wing test lets the wing break at a load factor of 1.54 (where 1.5 is the goal) on the first try, we are pretty good already. Same for performance: New models hit their predicted fuel consumption within 2%! And regarding the many subsystems: COTS. Of course, if you insist on re-inventing the wheel all over again for a new airliner, then those 10 years are acceptable.

* "Safe" meaning the one promising the highest bonus to management for the time they hold their position, and with their current state of incomplete knowledge. Sadly, the ethos of companies like Newport News Shipbuilding, whose motto was: 'We will build good ships here — at a profit if we can, at a loss if we must, but always good ships.' has been lost to the Harvard MBA culture with its focus on short-term results.