How Does an Aircraft’s ‘Black Box’ Flight Recorder Work?

by guest blogger Puri Ruiz

Much has been written about this small device that all commercial aircraft have been incorporating for more than half a century. And little wonder: “black box” flight recorders are essential in order to identify the causes of an accident.

We know, thanks to ironclad statistics, that the airplane is the safest means of transportation, but several decades ago there was a model of aircraft, the Comet, whose accident rate was well outside of normal range. It was the early 1950s and the experts wanted to know what they were due to. Australian chemist and aeronautical engineer David Warren was the creator of the first black box, and developed it based on a technology that recorded in-flight conversation. But back in 1939 there was a more rudimentary prototype, created by Frenchman François Husseno, with photographic film and calibrated with mirrors, to which sensors launched flashes that reflected on it and thus recorded the flight history. An interesting fact: it’s said that Hussenot, aware of the importance of his invention, hid the box near a beach on the Atlantic Ocean when the Nazis invaded France, so that they wouldn’t get hold of it.

From Warren’s device to today, black boxes have come a long way. To begin with, airplanes do not incorporate one, but two, both normally located at the rear of the aircraft. And each of them has a specific function:

  • FDR (Flight Data Recorder): this device records all those parameters that can be recorded on a commercial flight, such as altitude, course, speed, engine performance, etc. Most of these devices today record between 17 and 25 hours of data and are subjected to exhaustive reviews annually to verify optimal reliability.
  • CVR (Cockpit Voice Recorder): records the voices and sound warnings of the last two hours of the flight (or the last half hour, depending on the plane and the device) via microphones located in the upper part of the cockpit, so that we can also have spoken information. A standard CVR records four different channels of audio data. Of course, digitization has brought noticeable improvements to its manufacture. On the one hand, yesterday’s magnetic tapes are no longer used; these days all the information is stored in solid state drives, also known as flash memories, which can also keep this data for years, and have their own power supply that does not rely on the airplane’s.

Airplane black boxes also have an underwater beacon that emits geolocation signals for 30 days. Technology is advancing rapidly in this regard, and black boxes are getting better and better: since 2019, different aircraft have begun to be equipped with devices that capture up to 25 hours of sound recording, and due to their smaller size they can be placed in two locations: one at the front of the plane and the other at the rear. In this way, the possibilities of preserving all the information are much greater. Technological companies such as Leonardo or L3Harris are two of the leading companies in its manufacture.

But of course, all this would not make any sense without one fundamental thing: the extraordinary resistance of chosen materials. The FDR and CVR devices are protected by the CSMU (Crash-Survivable Memory Unit) system, which makes them virtually unbreakable for two reasons:

The materials. Titanium and steel encase and armor the recording system of both devices. Titanium is a metal with the best hardness-density ratio, very resistant to corrosion, fatigue and capable of being subjected to high temperatures without deforming. Steel has similar properties, although its weight is greater. People often ask why the entire plane could not be made from these materials: it would simply be too heavy to take flight.

The demanding resistance tests. In addition to the fact that these devices are periodically inspected, before being installed on aircraft they undergo numerous tests that certify their extremely high durability: resistance to fire, penetration, water pressure, crushing and strong impact.

All information stored in the FDR and CVR devices (that is, the two black boxes) is digitally extracted and processed in a specialized laboratory through sophisticated programs.

Finally, it is interesting to know why it is called a black box. The origin of this name is not entirely clear: some old prototypes of the British Royal Air Force were painted in that color, and others were a kind of camera obscura that incorporated photographic plates. But they might also receive this name based on systems theory, where a black box is an element that receives input and produces an output, or series of responses. Whatever the origin, black boxes aren’t even black but rather covered with a special orange paint, also highly resistant to corrosion and high temperatures.

Photo | narvikk