Originally Posted by
Luc Lion
If you re-read the Seattle Times article, you'll notice that it is only 2 bits flipping that are required for enacting the scenario.
Five bits have been actually flipped because this is the standard procedure for this category of tests ; flipping what is considered the most extreme and improbable data corruption : 5 bits simultaneously.
That's not what the article says:
"For these simulations, the five bits flipped were chosen in light of the two deadly crashes to create the worst possible combinations of failures to test if the pilots could cope. For these simulations,
the five bits flipped were chosen in light of the two deadly crashes to create the worst possible combinations of failures to test if the pilots could cope."
"In one scenario, the bits chosen first told the computer that MCAS was engaged when it wasn’t. This had the effect of disabling the cut-off switches inside the pilot-control column, . . . A second bit was chosen to make the horizontal tail, also known as the stabilizer, swivel upward uncommanded by the pilot, which has the effect of pitching the plane’s nose down. Other bits were flipped
to add three more complications.'
So the article clearly says that all five bits were specifically selected to create the simulated scenario. The three bits were not selected at random.
What is the basis for your statement that flipping five bits "is the standard procedure for this category of tests"?
As for MurphyWasRight's statement that the five-bit failure was a "rational stand in for 'something happens we have not though about'," my understanding is that the regulatory issue is that you cannot have a single failure that is catastrophic, and the FAA considered five simultaneous bit flips a single failure. If the only way to create the Seattle Times-reported scenario is to fail multiple components, then is it still a single failure?