>If someone at the FAA had made the effort to check the design of the flight control system,
That's not really how regulated industries work.
If the FAA had to check every line of code in Boeing's systems they would need more programmers than Boeing with more experience of the Boeing software design than Boeing itself. At this point why not just have the FAA design all aircraft ?
If the FAA don't trust Boeing's design, can they trust Boeing's manufacturing? Do they have to have an FAA inspector standing next to each Boeing machinist watching what they are doing? Does this extend down the supply chain to all subcontractors? Does the FAA have to have a guy in the mine watching somebody dig out the bauxite?
The point of ISO9001 and ISO13485 and ISO all-the-bloody-rest, is that you say what you are going to do and you do it in the way you said. At some point the regulators have to trust you.
It's the same reason you have traffic laws rather than a cop sitting next to every driver.