3 ms·

I can definitely concede there can be some asymmetry, but I think it's system dependent. As the Boeing 737 Max 8 shows, adding new items (in this case a new de

by dv_dt 8y ago

I can definitely concede there can be some asymmetry, but I think it's system dependent. As the Boeing 737 Max 8 shows, adding new items (in this case a new design element) is also fraught with risks. You have to get the root analysis correct when adding or removing elements. Adding has risks of unknown (not accounted for) like removing has risks of unknown (accounting forgotten). In the end, I guess I still believe the best strength is in good analysis at the consideration stage.

ngcc_hk 8y ago
I think the case of 737 max is they game the checklist approach - use the guy who should be checked to be the guy to check it. Hence the argument to remove an item is so dangerous. (But then it is also may be bad blood. Life is more complex than a checklist. )
brianpgordon 8y ago
Adding a design element is completely different from adding an item to a checklist. The asymmetry with checklists is that it's completely risk-free to add a new check, but it's risky to remove one. For example, someone might say "we're not totally sure that our system won't fail when we do X, so let's check that in QA, or at runtime, or at takeoff, or whatever." Now that the check is there, it protects you from failures when you do X. And now you're in a situation where you can't safely remove that from the checklist unless you can prove that your system won't fail when you do X. Adding requires only a suspicion, removing requires rigorous proof. The case you describe with the 737 Max isn't the same at all. There's an actual risk when adding a new component to the system, but no risk when adding additional verification. That's not to say that there aren't other costs, but it can't directly make your system less reliable.
- dv_dt 8y ago
  Just one example: If I add a step of, If patient enters with heart attack symptom X, was patient injected with 100cc of <drug>? It's not a risk free check at all. It will likely increase the rate at which the drug is administered, with all types of plusses and minuses associated with adding a component to a system.

by dv_dt 8y ago

ngcc_hk 8y ago

I think the case of 737 max is they game the checklist approach - use the guy who should be checked to be the guy to check it. Hence the argument to remove an item is so dangerous. (But then it is also may be bad blood. Life is more complex than a checklist. )

brianpgordon 8y ago

Adding a design element is completely different from adding an item to a checklist. The asymmetry with checklists is that it's completely risk-free to add a new check, but it's risky to remove one. For example, someone might say "we're not totally sure that our system won't fail when we do X, so let's check that in QA, or at runtime, or at takeoff, or whatever." Now that the check is there, it protects you from failures when you do X. And now you're in a situation where you can't safely remove that from the checklist unless you can prove that your system won't fail when you do X. Adding requires only a suspicion, removing requires rigorous proof. The case you describe with the 737 Max isn't the same at all. There's an actual risk when adding a new component to the system, but no risk when adding additional verification. That's not to say that there aren't other costs, but it can't directly make your system less reliable.

dv_dt 8y ago
Just one example: If I add a step of, If patient enters with heart attack symptom X, was patient injected with 100cc of <drug>? It's not a risk free check at all. It will likely increase the rate at which the drug is administered, with all types of plusses and minuses associated with adding a component to a system.