black box - flight recorder - flight data recorder

The Black Box Part 2

Martina Roters
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6 minutes

Why is everyone talking about the black box…

… when in reality the black box is not black, but bright red?

We have already reported on the history of the black box in the first part. Now we will answer some questions you might have already asked yourselves.

The black box consists of two large and one small component: The Flight Data Recorder (FDR) and the Cockpit Voice Recorder (CVR). The small component (ULB = Underwater locator beacon) is the underwater transmitter with which the black box draws attention to itself. This allows the rescue teams to find the crash site at all.

This is exactly the reason why it is not black like the shallows of a gorge or a sea, but bright signal red, so that it stands out well from its surroundings. Why it is called a black box, there is no unanimous opinion on this, but there are a number of theories. Here simply enumerated:

Black Box - Flight Recorder - Cockpit Voice Recorder
A flight data recorder (left) and a cockpit voice recorder (right) mounted in the rear fuselage of an aircraft. Each has an underwater locator beacon mounted in brackets at the front / © Wikimedia Commons – Yssy Guy

No. 1: Like a darkroom

An early development variant of the data recorder worked with picture exposure. This means that the inside of the recording box had to be pitch black, like in a darkroom – black box!

No. 2: Camouflage colour

During the Second World War, all components of airplanes were painted black so that they could not be recognized by the enemy by light reflection. Of course, this also happened with the black boxes – so they lived up to their name.

No. 3: Journalist’s word

In the memory of Peter Warren, the son of David Warren, inventor and advocate of the black box, an English journalist had said to Warren: “You have a wonderful black box there.”

No. 4: Fireproof paint

In the 1950s, some black boxes were reportedly painted with a fireproof paint that was black.

No. 5: Component with mysterious interior

In the 1960s, the term black box came up for components where engineers knew input and output but did not know what was going on inside the component. The data and voice recorders that came up at that time were the same, hence the term black box.

No. 6: Burnt and charred

© Wikimedia Commons – Aviation Safety Board Norway

How does a black box work?

According to international standards, every aircraft with a take-off weight of over 5,700 kg must have a black box on board. This is a good thing, considering the emotional pain that comes with the fact that relatives cannot find out why their loved ones had to die. Not to mention the criminal and insurance aspects. Furthermore, nobody feels comfortable when getting on a plane of the same type as a plane that just crashed and nobody knows what caused the accident. 

The black box – let’s stick with the naturalized term from now on – is usually located somewhere in the rear of the aircraft, because this is less endangered in case of a crash.

By law, the flight recorder records at least 88 different parameters, here are just a few important ones: time, speed, direction, altitude.

In reality, however, a high-tech device today can record thousands of data. The records run for 24 hours, then they’re overwritten.

The CVR not only records the voices in the cockpit, as the name suggests. There is also a microphone that picks up ambient sounds, for example a possible bang, hissing, or even voices of other people speaking in the cockpit. The recording lasts two hours, after that it is overwritten.

Of course, all this only makes sense if the black box actually “survives” a crash and the recorded data can still be evaluated.

What must a black box be able to withstand?

The housing is made of stainless steel or titanium and is fitted with a fire-retardant filling. Inside, there are no steel or plastic magnetic tapes anymore, but memory cards of immense capacity.

Black boxes are masterpieces of engineering, cost as much as a small car and must pass the toughest tests:

Impact test:

The black box must be able to withstand an acceleration of 3,400 G-force for 6.5 seconds. This corresponds to an impact speed of approximately 750 kilometres per hour. The test is actually performed with a cannon!

Black Box - Flight recorder
© Wikimedia Commons – Swedish Accident Investigation Authority

Penetration test

A steel tip that falls on the module at a height of three meters must not penetrate the wall of the recorder. That sounds harmless? But the falling object has a mass of 227 kilos!

Deformation test

2.5 tons act on the recorder from each side for five minutes. Nevertheless, the device must function intact inside.

High temperature test (fire test)

For one hour the recorder is held in a flame of 1,100 degrees Celsius (that’s how hot kerosene burns).

Low temperature test

The recorder is exposed to 260°C for 10 hours. Nevertheless, the unit must function inside.

Deep-sea test

The black box is stored for 30 days under deep-sea conditions: simulated water pressure of 6,000 metres in salt water.

Test with aggressive liquids

The box must also prove immune to all liquids used in an aircraft, such as oils, fuels, acids, alkalis and even fire extinguishing agents, for 48 hours.

Not only for the extreme emergency

In an emergency, data overwriting is prevented by an accelerometer or the interruption of the power supply (tearing off or braising away of the current-carrying cables).

However, the records are not only useful for crashes, but also for other serious danger situations, such as “near-collisions in the air”. For this reason, the crew also has a switch with which they can manually interrupt the power supply to the voice recorder and thus prevent the recording from being overwritten.

The records of the flight data recorder are sometimes evaluated even when nothing very serious has happened yet: by the maintenance engineers who have their eyes on a particular component approaching the end of its service life.

An intermediate step into the future

Only a black box that can be found is a good black box. The manufacturer Airbus is working on a black box that “catapults” itself away from the aircraft in case of a crash over land or water. And it should be able to swim, not, as is currently the case, wait in secret for its discovery somewhere on the seabed.

A better solution?

But isn’t there a better solution to the problem?

If we’re going by the word “crash”. What does the average consumer do when he wants to protect his hard drive data from a crash and the associated data loss?

Right. He just sends his data into the cloud.
So why don’t the airlines do the same and transmit the flight data directly to headquarters via satellite instead of still storing it in the old-fashioned black boxes?

In some cases they already exist, such transmissions from the onboard network systems of the aircraft. The problem is that satellite transmissions are expensive and capacities are limited.

In addition, questions will certainly also arise about the possible manipulability of the data. The data of the good old black box was at least “hackerproof” down there at the bottom of the sea…

Here, the Black Box is again explained in detail by Captain Joe:

Titelbild © Wikimedia Commons Mattes 1

by Martina Roters

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