5 ms·

that's not how safety margin work, is not a budget leftover set aside for known unknowns, it's there for unknown unknowns. e: downvoters might want to read Fey

that's not how safety margin work, is not a budget leftover set aside for known unknowns, it's there for unknown unknowns. e: downvoters might want to read Feynman again "If a bridge is designed to withstand a certain load … it may be designed for the materials used to actually stand up under three times the load … But if the expected load comes on to the new bridge and a crack appears in a beam, this is a failure of the design. The O-rings of the solid rocket boosters were not designed to erode. Erosion was a clue that something was wrong. Erosion was not something from which safety could be inferred" if you fail a test before your margin you haven't established that your safe up to 90% margin, you've established that the hypothetical on which your design was based are wrong and no further inference might be warranted, regardless of whether you fail at 99% or 60% of where you expected to fail

tempestn 7y ago
That doesn't apply in this case. Modeling will never be a perfect representation of reality. IE you're never going to have tested failure at 100.00% of the expected failure load. If it had failed at 90% I would agree that they should take another look at the design, but at 99% it's within expectations. And you still maintain essentially all of the designed safety margin for the unknown unknowns.
alkonaut 7y ago
They didn't get a pass at 99%.
- LoSboccacc 7y ago
  I didn't address my reply to FAA either
perl4ever 7y ago
You aren't paying attention to the phrase "expected load". If, in the bridge scenario, it cracks under 2.95x the normal load, vs. 3.0x or 3.05x, that is not what Feynman was describing. He was explicitly talking about a partial failure under about 1.0x. Which based on other comments is not what happened here.
- LoSboccacc 7y ago
  except 3.75g here is the expected load°, the certification requirement. the design is engineered to reach that 3.75g°, the safety margin is what lies beyond. °with the disclaimer that the plane might be not airworthy after landing

tempestn 7y ago

That doesn't apply in this case. Modeling will never be a perfect representation of reality. IE you're never going to have tested failure at 100.00% of the expected failure load. If it had failed at 90% I would agree that they should take another look at the design, but at 99% it's within expectations. And you still maintain essentially all of the designed safety margin for the unknown unknowns.

alkonaut 7y ago

They didn't get a pass at 99%.

LoSboccacc 7y ago
I didn't address my reply to FAA either

perl4ever 7y ago

You aren't paying attention to the phrase "expected load". If, in the bridge scenario, it cracks under 2.95x the normal load, vs. 3.0x or 3.05x, that is not what Feynman was describing. He was explicitly talking about a partial failure under about 1.0x. Which based on other comments is not what happened here.

LoSboccacc 7y ago
except 3.75g here is the expected load°, the certification requirement. the design is engineered to reach that 3.75g°, the safety margin is what lies beyond. °with the disclaimer that the plane might be not airworthy after landing