Originally Posted by
.Scott
Having programmed in machine language, I would NOT recommend it. It would be very difficult to reach the level of confidence for direct machine code (or even assembly) that would be required for this software.
The sequence would be: requirements, requirements review, design, design review against the requirements, test development based on the design, test procedure review, coding, code review, code testing. This requires code that can be examined by several team members with no chance of misinterpretation.
I fully agree, as an example the automotive functional safety process has the following steps:
-> Hazard & Risk analysis
-> Functional safety concept
-> Technical system safety concept
-> System achitecture
-> Technical Software Safety concept
-> Software architecture
-> fine design
-> implementation (code writing)
-> Module test
-> SW integration test
-> System integration test
-> System test
-> Vehicle Integration test
It is recommended to write technical safety documents in formal language to exclude misinterpretation. Implementation is less than 10% of the work. Toolchain qualification is also an important part of the process. Even the best compiler may cause errors if the memory module within the programmer's laptop has defective bits... (Yes, it already happened).
All documents are to be reviewed, accessed, there are walkthrough meetings and so on. All requirements need to have verification criteria specified together with the requirement and test cases are later based on there criteria... Within accessments, certain levels of safety require a certain independence between accessor and author (other team, department, division, company...).
Safe code can be done and if this was skipped just because one feared a diagnosis (AoA disagree), reaction (deactivate MCAS) and pilot teaching (continue flying, you probably never need MCAS anyway), this is a violation of safety culture beyond my imagination.
Fun fact: Emission standards for cars (onboard diagnosis 2) require 2 out of 2 for every sensor which may cause the violation of emission standards (ULEV, EU6...) and the engine control light on disagree. Seems like this is more important than a few hundred airplane passengers...
Oh, just one question:
People claim that the manual trim may not be operable in certain flight conditions while the electric trim motor is more powerful.
On the other hand the manual states that in case CUTOUT does not work, one should grasp and hold the wheel (?against the motor?). Did I miss something?