Extension or Break?

Boeing's 737-MAX story is probably going to be the biggest fail of 2019, with the flight ban unlikely to be lifted anytime soon. I would be far from blaiming Boeing doing all that deliberately, as many are saying. Something else happened instead.

Boeing was caught off guard. 737 was the most successful program in the company history and whatever they would planning was considered an extension of that success. It turned out, however, the MAX changes touched deeply into the architectural design of the aircraft. And the MCAS system went from an auxiliary augmentation feature, never considered flight - critical, to becoming absolutely critical. And Boeing failed to categorize MCAS as critical, as it should have right after the planes were grounded. So first they fixed the angle. Then they added the input from the secondary AoA sensor. And now they are reportedly redesigning the system to make use of BOTH flight computers simultaneously. Redesign after redesign after redesign. That could have been avoided if they analyzed and categorized the system as flight critical in the first place.

I see similar stories elsewhere too. Without calling names, there is one very popular and well established wired device control standard. And it now wants to move to wireless. So they designed a wireless adaptation layer, making sure all the application - layer frames would be nicely encapsulated and carried over other physical medium. Apparently, what they failed to realize, is there has been one property of the current physical layer they use, which is no longer present on the new physical layers.

The current PHY is reliable. The new ones are not. This has severe consequences. What used to work for many years no longer will. And guess what - nobody has tested that. Caught off guard like the Boeing MAX. A development that has been considered and planned as an extension turns out to be changing the architecture fundamentally. In a way that things will break. And the only way is to redesign the architecture, acknowledging the change is not "just" an extension.

It is an interesting story and I do hope the 'MAX similarity will serve as the warning sign for the designers to think twice, test and implement the architectural changes required so the move to the next generation will be successful.