e.g. volcanic ash is also an environmental trigger. But it is likely to certain to cause engine failure. No amount of ash is acceptable, but there is a density at which engine failure will happen quickly, and it's going to affect all engines at pretty much the same time. So in this extreme case, certain probability of engine failure in the triggering conditions means you have no redundancy with additional engines.
Whereas the problem sounds more variable and complex. Probably is low, therefore additional engines does provide redundancy just not as much redundancy as being in non-triggering conditions. Decent chance there's enough time to find another altitude to avoid additional failures.
That's not very reassuring to me. The article is light on details, but this bug is apparently triggered "during a step climb to a higher altitude in ice crystal icing conditions." The fact that the plane can operate one one engine doesn't do much good if both engines fail due to the same bug because they're experiencing the same conditions at the same time.
How is it that they can't pass those on to GE? You'd have to figure that if you've got your own SLA, you'd want an SLA on upstream providers.
looks like the bug is know but they plan to deploy a fix to the airliner after it enters production, for reason unknown to me (likely having to restart some certifications?)
"The root cause of this event is the fact that ICI [ice crystal icing] accommodation logic, as itβs currently certified, is suspended with the application of climb power"
However, thanks to how the industry is regulated, Boeing don't take chances if there is a risk to passenger safety. In this case, the likelihood of a single engine shutdown due to this elusive bug + the failure of the automatic restart system + the failure of the manual restart procedures, _combined with the fact that all commercial aircraft needs to be able to operate with only one of the engines_, makes Boeing ask for the exemption.
The FAA, on their part, is 100% right in demanding that Boeing show their work and is unlikely to grant such an exemption unless the risk is calculated to be negligible.