|First, I'd like to thank once again CM,|
tdscanuck, rcair1 and others for informative posts. I would also like
to welcome b2319 to a.net, your post certainly got me thinking about
containment and relief valves as far more complex beasts than I had
thought before. Thanks.
Second, I have a plea that this thread would not descent into political
speculation or accusing NSTB or FAA of misbehaviour. They are one of the
most respected organizations in the world in this area, and it would
be, IMO, unthinkable that they would be misbehaving any way. They are
the true experts. They have all the information that we do not have here
in a.net. Exact state of containment systems and other equipment in the
bays, for instance. If they say they need to ground the plane, they
have a reason to do so. Even if it is just not being certain that no
other damage occurs in some (perhaps obscure) other scenario than the
one played out in the two incidents. Let them do their work.
And now to the topic of my post. I'm trying to understand different scenarios for lifting the grounding.
Scenario 1: Operational changes
ETOPS limitations, in-the-ground inspections, lower thresholds for
diversion, perhaps some battery usage/charging changes in flight. If
these procedures would be sufficient, the grounding could have been over
in days. I can only conclude that either these procedures are
insufficient, or that the NTSB does not understand the events well
enough to allow the grounding to be lifted yet. Obviously, the root
causes need to be found.
Scenario 2: Battery manufacturing quality
A problem is discovered in battery batches and/or manufacturing process,
the issue is fixed and the planes start to fly again. If this was the
solution, we could see the end of the grounding in weeks, particularly
if defective batteries can be found by testing.
I think this is somewhat unlikely as the only fix, as I suspect the NTSB
wants to understand how well the containment works in the eventual
cases that even with high-quality batteries, there can be a thermal
runway in one of them some day.
Scenario 3: Battery charging systems
Or perhaps these systems misbehaved in some way. A fix to them would be
an engineering (and re-certification) process. In the best case this
would take a few months, in the worst case more. I remember that the
battery system manufacturer took seven years to design the current
batteries. In my opinion, that is a very long time, and changing a
component should be possible in months.
Charging system issues is a possible root cause, but it is looking a bit
unlikely perhaps, if the early reports are true that the batteries were
not overcharged. That being said, if the per-cell history of events
burned down with the batteries, how would we know?
Scenario 4: Containment structures
It is probably not sufficient to fix the containment structures, but if a
battery manufacturing fault is found, fixed, and the containment is
enhanced to make the NTSB/FAA confident that it works in all cases, then
the plane cloud clearly fly.
It is difficult to estimate how long this would take. A steel plate
"shower curtain" would be very easy to add. Certification, analysis that
it works in all cases would probably take longer. I'd say months.
A more significant modification, such as fluid venting out of the
aircraft or even enlarging or moving the battery containment structure
could take much longer. Half a year for venting out, years for moving
the structure or making the EE bay larger to fit the new containment
structure. FWIW, I think the shower curtain is probably going to be
Scenario 5: Electrical system
Or maybe there is some issue with the electrical system that is causing
trouble for the batteries. If this is the case, it would be very
difficult and time-consuming to understand and fix the issues. But as an
engineer, I find it difficult to believe this to be the case. Surely
the design has voltage and current regulators that isolate the quality
of the aircraft electricity from the quality of the electricity fed to
But if they need to do something with the electrical system, it could
take years. Adding a more high-quality regulation circuitry could be
easy, however, maybe only months.
I think the issues are somewhere in categories 2 through 4. If a battery
or charging system fault can be identified and a slightly enhanced
containment put into place, the plane should fly in 4-6 months, if not
sooner, at least as a temporary measure for current frames. And a more
intelligent new containment adopted for future frames.
But it is also possible that once the events are understood, the current
containment system is deemed adequate (as tdscanuck and CM
believed early on in this thread). Then the critical time factor is
understanding why the batteries failed, and I'd predict that to take
some number of months anyway.
In the other extreme, it is also possible that the containment system
needs a significant change. If no intermediate solution can be found,
this could drag on for over a year. (Interestingly, according to
Wikipedia, A350 should enter service mid 2014. If the worst comes to
worst, we could see the 350 fly commercially before the 787 is back in
the air. But I do not believe this to happen.)
Finally, I should add that none of this is rocket science. Batteries and
charging systems are well understood. And the energy levels for
containment are still... small, when you consider the size and energy
content of the device. It is some number of times bigger than a car
battery, not a nuclear bomb. Boeing engineers know how to enhance it, if
it needs enhancing.