What's in plane's legendary black box?

In past few days, crash of China Eastern Airlines passenger plane MU5735 has touched people's hearts. The key to finding out truth about accident lies in black box.

Before we start, answer two questions: Why is black box orange? Why is it called a black box?

Everyone can guess color problem. The orange color is more recognizable and easy to find and locate. After all, it stores very important flight data.

As to why it's called a black box, it's widely believed that it's because the way it works is relatively simple and only requires input. As for what's going on inside, it's impossible to know, which is a bit like a "blind box".

Then some people will ask me if one I dismantled fell from a crashed plane→_→

If he really fell from a crashed plane. So for now the black box should look like this:

Or like this↓

So don't worry, it's usually a decommissioned black box.

Next, let's do a little extra homework, otherwise it will be a little hazy to watch disassembly later.

There are two main black boxes in aircraft - FDR and CVR.

Top - FDR, bottom - CVR

A flight data recorder (FDR), commonly referred to as a flight data recorder in Chinese, is basically a device that records data of various indicators and parameters during flight of an aircraft. Generally speaking, most of black boxes are FDRs, which is most important direct evidence in an accident investigation.

Cockpit Voice Recorder (CVR), Chinese usually translated as cockpit voice recorder. In human terms, it is a tape recorder that is used to record radio calls, conversations between pilots, and environmental sounds.

It's a pity that this time it's not FDR, but CVR, so it looks relatively simple.

The CVR is broadly divided into three parts: FDAU, CSMU, and position beacons.

Flight Data Acquisition Unit (FDAU), translation must be a Flight Data Acquisition Unit, which is a base part with straight edges and corners that is used to communicate with aircraft related data bus to obtain appropriate data and encoding. This.

The Crash-Survivable Memory Unit, which should be called Crash Data Storage Unit in Chinese, is orange cylinder above, which is actually used for data storage, and accounts for 70% of weight of entire black box.

The last small cylinder attached to CSMU is an underwater radar device (underwater radar device) that automatically activates and sends a positioning signal when it encounters water.

Having done our homework, let's get a general idea of ​​the model we've disassembled this time. This is a CVR from L-3 Communications, model FA2100. Appearance is exactly as in picture:

The thing looks small, but weight is very touching, and bulk of weight comes from raised CSMU.

According to design parameters of this CVR, its operating temperature can be from -55℃ to 70℃, and it can withstand:

5000 pounds of pressure

One hour continuous operation at 1100℃ high temperature

Ten hours continuous operation at 260℃ high temperature

Influence of 3400G acceleration

Without losing any data, this is a super powerful USB flash drive overall!

Let's see what's inside!

First, remove protective cover protecting service port, then remove surrounding screws securing CVR itself.

Remove all screws and tighten them one by one without panic.

At end of disassembly, it turned out that CSMU needed to be removed before continuing to remove top cover of FDAU, so I unscrewed 4 huge bolts, lifted it vertically and removed connecting cable to remove entire KSMU.

I only have regular precision tools at home, I don't have a wrench that size. Having removed it, first thing you see is two DSP TIs, we will talk about this later, but first we will continue to disassemble.

Lift top cover and set it aside, remove screws securing circuit board, and you can then remove entire bottom board. The whole board looks dirty, but it's actually quite clean. Everything is glued, but it looks more like some kind of resin. As for reason for glue, I think I should know it by heart!

There are still a few not removed boards in interface part, we continue to remove second half...

There are two boards on side, and something else under them. So keep fucking...

Remove first board which is a few logic circuits with main control in middle.

The second board should be responsible for power supply, I still see this to some extent.

It's a capacitor (?) pasted on sidebar, you must be right?

Sure, there's something on other side of power board, but it's basically a circuit connected to the power supply. There's also a lovely toroidal transformer, which isn't surprising given that this thing can run on both 28V DC and 115V AC.

All boards, without exception, are carefully glued and fundamentally not damaged by liquids, while boards are connected by connectors, which is convenient for maintenance and replacement.

The next step is to dismantle CSMU. Given that production date is end of last century, solid-state records will most likely be used.

Tear off cushioning foam at bottom, and there are four large screws, so it took a lot of effort to unscrew them all...

Handwritten serial number on a small ponytail. Same as on sticker. All this must be manually assembled, calibrated and configured. The degree of care in special equipment is different.

Remove bottom cover and you can check if solid state media used in this device is being used for recording. The surrounding circle should be a thermal insulation layer and shock absorbing material, and black on top should be same, but material seems to be different.

I picked it up with my hands, and it felt like some kind of mixture of asbestos and polystyrene, very light. The overall function is mainly thermal insulation and cushioning.

I must say that this thing is much smaller than I imagined. After it is taken out, there is practically nothing inside that can be taken out, it's all black foam.

It really took a lot of effort to protect this cylinder, which shows importance of contents inside.

Without further ado, go straight to screwdriver and unscrew all screws on cylinder. The top cover can be detached.

It is not surprising that interior is a multi-layered multi-level structure. It is tightly fastened together with 4 racks and screws.

The main control is on left and FLASH is on right. Well, it's time for a no-prize quiz, which company made flash used in this black box?

Expand answer:

Supplier moved to Intel.

To be honest, I was a bit surprised that they were Intel particles.

Despite everything, taking them all apart and lining them up in a row is a bit spectacular.

According to date on label, it should have been assembled in 21st week of 1998, and chip itself was manufactured in 1997. This is a good SLC chip in Intel product line.

Achieving 10,000 erasures in that era should be considered a good level. Working temperature is 0°C to 70°C, it should be wide particle temperature.

However, there is a 182°C sticker on top cover, which means data inside is dangerous when internal temperature reaches 182°C is not very clear.

Finally, see what master control you're using. As I suspected, it was a custom chip, and it seems that reusing entire module is basically impossible.

To calculate total capacity of entire module, 8x15 is 120MB, recording 4 audios for 30 minutes, basically consumes 1MB per minute?

Finally, let's go back to this picture again, let's not talk about two TI chips in middle, they should be used to process analog microphone signals, one chip is responsible for two channels, two in upper left corner and lower right corner of DSP. The black chip should be DRAM cache for DSP.

The controller with sticker in middle should be main controller FDAU from QuickLogic series (quick series), which is essentially similar to current FPGA. It's a highly customizable ASIC, but its flexibility is not as high as that of an FPGA. My personal understanding is that it's a custom made chip.

Apart from this, there are several other large chips that QuickLogic also makes, in which a whole set of solutions had to be applied.

I used to think about buying a maintenance tool kit to read information in it. I later checked internet and cheapest quote was around $40,000. I think it should be parsed directly.

Disassembled wreckage looks like this. In fact, design of this thing is not very complicated. I still have impression of solid materials and some detailed constructions. In future, I will find a way to parse it using FDR. Solid state CVRs are easier.