|Quoting packsonflight (Reply 42):|
As I understand this, the special condition say that battery fire should contained and not pose a danger to other system, and this goes for the whole flight envelope with no exceptions.
The "exception" is the "extremely remote" stipulation...the FAA didn't require 100% protection, as they do for any single failure, but allow a (very small) probability of multiple things lining up. I don't see why turbulence wouldn't enter into that fault tree, as they do with lightning.
|Quoting beau222 (Reply 43):|
Does the 748 series use the same type of battery or batteries that the 787 is having issues with?
|Quoting Aesma (Reply 45):|
You just made me think of something. You're talking about the venting of the battery itself, but what about the outflow valve ? If that gets blocked, then there is nowhere to go for the smoke except in the cabin/cockpit.
There's another outflow valve (forward bilge) and overpressure relief valves (just below the main deck floor). The outflow valves are also large...it would take an extremely big piece of debris to fully block them.
|Quoting cornutt (Reply 46):|
Although if the outflow valve was completely blocked, I think the whole aircraft would quickly be in trouble with over-pressurization. I assume there are over-pressure relief valves, but I have no idea where in the aircraft they might be.
They're on the left side forward, I believe, just below the main deck floor.
|Quoting seahawk (Reply 51):|
Well, I would say the containment worked reasonably in the first incident, but failed in the second. Flammable liquids (or paste) must not escape the containment.
That's *not* a requirement of the special condition. In fact, by the way the special condition is written, it's explicitly allowed.
|Quoting seahawk (Reply 51):|
It is like the containment of any storage tank for flammable liquids. If the tank fails and burns and the material burns inside the containment, the safety design works. If the tank just releases the material and it escapes the containment, the safety design failed, even if the material never burned in that incident.
The object is to make sure any release is harmless. Normal flammability containment isn't pressure tight, it has to vent something or it needs to be built as a pressure vessel.
|Quoting mham001 (Reply 63):|
I do think however having the BMS in the same box is absurd. This would not have have happened were I in charge of that design.
The farther you move the BMS from the battery, the more potential failure points you inject into the fault tree. Given the extremely tight requirements the FAA put on the BMS, integration with the battery was probably, by far, the most reliable available option. The fact that the BMS was destroyed in the fire isn't that significant, since once a thermal runaway begins the BMS can't do anything about it anyway, it's too late.
|Quoting sankaps (Reply 67):|
Boeing and FAA officials decided that since design and testing of the plane was so far along, mandating the tougher standards would disrupt years of joint safety work and unfairly delay production of the cutting-edge Dreamliners, said people familiar with the details.
Before everybody freaks out, note that this is how virtually all certification is done. They freeze the certification basis at a point in time (usually when the OEM notifies the regulatory that they're pursuing a new or amended TC
) and agree to hold it there for a fixed period (usually 5 years) so that the OEM's have some design stability. Changes in the interim are assessed against the certification basis and they only roll in new requirements if they believe there's a really compelling need to do so. In this case, the FAA had no reason to think the existing standards weren't tough enough.