Mike Sinnett: My name is Mike Sinnett. I’m the vice president of Engineering and the chief project engineer for the 787 program. There’s been a lot of interest in what an electrical power system is on an airplane and how our power system is different than other airplanes. And then what role the batteries play in the power system.
There are many systems on airplanes that need power; flight controls, avionics, air conditioning, in-flight entertainment. All of these systems on the airplane use electrical power. And because the airplane carries batteries, but only enough for some very small loads, we have to generate power while the airplane’s in the air. And then we have to safely distribute that power to the other systems on the airplane.
Now, there’s a schematic view of the 787. One of the things you’ll see is that there’s two generators on each engine and two generators back on the auxiliary power unit. There are six generators in the 787 that provide primary electrical power versus the three on a conventionally configured airplane for the provision of electrical power.
Besides just more efficient energy conversion there’s some other things that come along with the capabilities of the system, like better control of the power, better switching capability, better ability to balance loads and to manage loads. It helps us manage redundancy better than we’ve been able to before.
The other thing that you can see is that that power, instead of being taken all the way to the forward electrical equipment bay is taken to an aft electrical equipment bay.
Now, a lot of questions about the batteries and what the batteries do on the airplane. The batteries on the 787 – there are two large batteries. One is the main battery located in the forward electrical equipment bay. The other is the APU battery located n the aft electrical equipment bay.
There is a general impression that our batteries do more than they really do. I’ve had people ask me, do the batteries run the engines? No, they don’t run the engines. Do you use the batteries to start the engines? Nope, we don’t use the batteries to start the engines. We use the battery, the main battery, when you walk out to a cold dark airplane and want to start it up.
The APU battery is used to start the APU. Once the APU is running, the APU powers its own fuel unit and all that APU battery is doing is providing power to the APU controller.
This is an expanded view of what the 787 battery looks like. This is an indication of the complexity of the battery. It’s made up of eight cells. Each of the cells is essentially a four volt cell, which means that the battery is a 32 volt battery.
We’ve got multiple layers of protection to keep the battery from ever being overcharged. And the same is true for things like where the voltage could get too low, or charging at too high of a current, or charging it too low of a temperature. So there are a lot of protections that are built into the battery. And it also can be stored for longer than a NiCad battery can.
Just Comparing the 787 battery with the 777 battery, you can see it’s a 32 volt, 8 celled battery. The 777 is a 24 volt 20 cell battery. The 87’s battery weighs 63 pounds compared to 107 pounds. And we can provide 150 amps of power up versus a lower power requirement on the 777. So these were some of the design characteristics that were considered when we chose lithium-ion technology for the 787.
We never take a technology and ask, how can we put that technology on an airplane? It’s always driven by the need of the airplane. And so any of the technologies that made their way into the 787 – and in fact, I’ll say any technology that makes its way onto any Boeing airplane – earns its way on.
A lot of testing went into these batteries. More than 5,000 hours of testing in the lab of these batteries. 25,000 hours of other integration testing that included these batteries in the testing and more than 10,000 hours of flight test and ground test with these batteries on the airplane.
Now, obviously everyone’s aware of the two incidents we had in January. We had an APU battery fault and we had a main battery fault. Those happened within just eight days of each other. We believe we had very rigorous protections designed around the battery and were in the process now of working with the investigators, both the NTSB in the United States and the JTSB in Japan to try to better understand what potentially could cause those failures.
You know, the one thing that I’d like to say as we’re working our way through this problem is we’re conscious of a couple of things. Safety absolutely is our highest priority and we never move forward until we’re convinced ourselves that the fleet going forward is as safe as we intend it to be. And that’s why we’ve got hundreds of people working around the clock, 24/7 to make sure that we understand what’s going on here and we return the fleet safely to commercial flight.