"This all comes after CNN cited unnamed sources in reporting that while testing a supposedly fixed version of the MCAS software in a simulator, pilots found that a microprocessor in the anti-stall system would lock up. As a result, the plane would pitch down and, for several seconds, the pilots would struggle to regain control. Presumably the new software was run on actual MCAS hardware within the simulator, triggering the hardware freeze.
To us, it sounds as though code in the MCAS update either forces the processor into a locked state, such as a tight unbreakable and uninterruptable infinite loop, or triggers an exception that can’t be handled and the CPU halts. It is remotely possible the code encounters a design flaw in the unidentified microprocessor that causes the circuitry to freeze."
My take is that the simulator runs the same software on the same hardware as the actual plane, which would make sense. And the software fix probably fixed the problem it was supposed to fix, but somehow borked something else.1)
This still leaves the systems that provide the simulated input for the simulator as a potential source for problems, though.
Sounds like debug hell.
1) There is a German expression for that, verschlimmbessern.
The reason for the MAX existing is Boeing making a desperate rush to preempt the market start of the Airbus “neo”. They did this by slapping a modern, but too large engine on a frame that was never designed for it. The result was an aerodynamically unsound plane, that would probably not have been approved in “the olden days”. However we live in the gizmo age, and they “solved” the problem by putting in MCAS, that will force a control surface movement upon detection of a critical flight attitude and -speed, to cheat around that unsafe spot in the flight envelope. The inputs to MCAS are comparatively primitive though. I could be wrong, but to my knowledge, it does not know or care about the altitude, landing gear or flap configuration, let alone forward terrain or flight regime. As a result, there are flight situations where MCAS’ automatic “fix” to the sub-par aerodynamics can only create a disaster. Perhaps this could be solved electronically, but it would require a far more advanced system than MCAS, that takes a lot of additional factors into consideration. The proper way to solve this however, would be to design a proper, modern airframe to fit those modern engines. But Boeing’s management and shareholders have staked the project, and maybe the whole company, on exactly not doing that to get one up on Airbus. Now what do you do.
An absolutely stupid and terrifying business decision. Further, the primary reason they did it was to not require retraining and recertification of pilots. If you can fly a 737, you can fly a Max, was the reasoning. I never want to fly on one. They’re solving a fundamental design flaw with a shoddy software patch. It’s inevitably going to crash again if they recertify it.
Boeing’s 737 Max Software Outsourced to $9-an-Hour Engineers
Increasingly, the iconic American planemaker and its subcontractors have relied on temporary workers making as little as $9 an hour to develop and test software, often from countries lacking a deep background in aerospace – notably India.
The coders from HCL were typically designing to specifications set by Boeing. Still, “it was controversial because it was far less efficient than Boeing engineers just writing the code,” Rabin said. Frequently, he recalled, “it took many rounds going back and forth because the code was not done correctly.”