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Of course Boeing want to deliver the planes, otherwise they get hit by significant late delivery penalties. However, thanks to how the industry is regulated, B

Of course Boeing want to deliver the planes, otherwise they get hit by significant late delivery penalties. 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.

ken 8y ago
The problem sounds to me like it's triggered by environmental conditions, not random chance: "during a step climb to a higher altitude in ice crystal icing conditions". In that case, does having two identical engines really constitute redundancy?
- eloff 8y ago
  Exactly, are we looking at correlated or uncorrelated risk here, because that makes a huge difference!
- cmurf 8y ago
  As the probability of a condition triggering failure increases, there is a decreasing probability that redundancy helps. 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.
gizmo686 8y ago
The bigger issue for the FAA is culture. Flight is so safe because all of those safty measures are taken seriously. Whenever exceptions are made, there is a risk of normalizing devience, and standards will slowly erode until a disaster shakes us back (and even a disaster is no guarantee to a return to anything near our current level of standards.) Building a safety culture as strong as aviation is hard, and the FAA doesn't like risking it.
JackFr 8y ago
> Of course Boeing want to deliver the planes, otherwise they get hit by significant late delivery penalties. 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.
- cma 8y ago
  Maybe GE has offered to pay them a huge amount if Boeing can avoid hitting GE with the SLA penalties. From Boeing's POV, the lost profit of not getting paid off by GE would be as bad as the loss from not having an SLA in place with GE.
  - anamexis 8y ago
    So GE would avoid paying SLA penalties by paying them an amount equal to the SLA penalties?
    - cma 8y ago
      I shouldn't have said "as bad". I'm sure they would take some hit. Maybe half on average, I'm not sure what negotiation theory would say.
394549 8y ago
> In this case, the likelihood of a single engine shutdown due to this elusive bug ... _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. 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.
LoSboccacc 8y ago
https://www.flightglobal.com/news/articles/boeing-requests-waiver-to-avoid-787-10-certification-447937/ https://www.flightglobal.com/news/articles/boeing-requests-w... 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 it’s currently certified, is suspended with the application of climb power"

ken 8y ago

The problem sounds to me like it's triggered by environmental conditions, not random chance: "during a step climb to a higher altitude in ice crystal icing conditions". In that case, does having two identical engines really constitute redundancy?

eloff 8y ago
Exactly, are we looking at correlated or uncorrelated risk here, because that makes a huge difference!
cmurf 8y ago
As the probability of a condition triggering failure increases, there is a decreasing probability that redundancy helps. 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.

gizmo686 8y ago

The bigger issue for the FAA is culture. Flight is so safe because all of those safty measures are taken seriously. Whenever exceptions are made, there is a risk of normalizing devience, and standards will slowly erode until a disaster shakes us back (and even a disaster is no guarantee to a return to anything near our current level of standards.) Building a safety culture as strong as aviation is hard, and the FAA doesn't like risking it.

JackFr 8y ago

> Of course Boeing want to deliver the planes, otherwise they get hit by significant late delivery penalties. 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.

cma 8y ago
Maybe GE has offered to pay them a huge amount if Boeing can avoid hitting GE with the SLA penalties. From Boeing's POV, the lost profit of not getting paid off by GE would be as bad as the loss from not having an SLA in place with GE.
- anamexis 8y ago
  So GE would avoid paying SLA penalties by paying them an amount equal to the SLA penalties?
  - cma 8y ago
    I shouldn't have said "as bad". I'm sure they would take some hit. Maybe half on average, I'm not sure what negotiation theory would say.

394549 8y ago

> In this case, the likelihood of a single engine shutdown due to this elusive bug ... _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. 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.

LoSboccacc 8y ago

https://www.flightglobal.com/news/articles/boeing-requests-waiver-to-avoid-787-10-certification-447937/ https://www.flightglobal.com/news/articles/boeing-requests-w... 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 it’s currently certified, is suspended with the application of climb power"