What does the black box on an airplane record?

In the mid-1950s, while investigating a series of mysterious accidents involving the de Havilland Comet - the world's first commercial jet aircraft, young scientist David Warren came up with a bold idea: to build a device that could record all flight data.

He envisions a device that can store parameters such as speed, altitude and especially cockpit sounds to know what the pilot said and how he reacted right before the accident happened.

Warren was 28 at the time and working at the Aeronautical Research Laboratory in Melbourne, Australia. Although the idea was not widely accepted at first, the black box laid the foundation for one of the most important tools in modern aviation.

Since then, the black box has become an indispensable device in every aviation accident investigation, from commercial aircraft to helicopters. So what does the black box actually hold?

Black boxWhat is that?

The flight recorder, commonly referred to as the "black box," actually consists of two separate devices, a flight data recorder (FDR) and a cockpit voice recorder (CVR).

While the FDR tells us what happened, the CVR helps reveal why it happened, says David Esser, an aeronautical scientist at Embry-Riddle University in Florida. It is the combination of technical data and cockpit audio that has become the key tool in deciphering airline accidents.

Typically, the data recorder is located in the tail of the plane, an area more likely to survive a crash, while the voice recorder is located in the cockpit to record conversations between pilots as well as unusual sounds such as system warnings or engine noise.

Both devices are equipped with underwater locator beacons, which help to quickly locate aircraft that crash into the sea.

Although called "black boxes," the devices are painted bright orange to make them easily identifiable in the rubble.

In terms of durability, Abdalla Elazaly, an advanced systems engineer at Honeywell, which makes black boxes for companies like Boeing and Airbus, said the devices are designed to withstand high impacts, extreme temperatures, explosions and deep water pressure. The casings are typically made from titanium or stainless steel, which are extremely durable materials used in the aviation industry.

But nothing is infallible. Elazaly said that in extreme situations, such as a total power outage, a high-speed crash, or prolonged immersion in deep water, even the black boxes could be damaged or unrecoverable. But even so, they remain vital in post-crash investigations.

What does the black box record?

According to the US National Transportation Safety Board (NTSB), many modern flight data recorders can store at least 88 important parameters about the aircraft's operation, from flight time, altitude, wind speed to thousands of other technical details, continuously recorded for the last 25 hours of flight.

Some advanced devices can even track more than 1,000 data points inside an aircraft, supporting in-depth analysis during crash investigations.

For example, the machine can record whether and when a smoke alarm was triggered, the specific position of the flaps, or when the plane switched to autopilot. This information helps experts accurately reconstruct the flight before the accident.

Meanwhile, the cockpit voice recorder (CVR) focuses on capturing sounds and noises in the cockpit, from engine noise, landing gear noise, switches, to audible warnings and pilot conversations. This device is usually connected to a ceiling-mounted microphone located between the two pilots, ensuring that all important sounds are recorded.

According to regulations of the US Federal Aviation Administration (FAA), all commercial aircraft are required to be equipped with a cockpit voice recorder capable of continuously recording at least 25 hours of flight time, helping to ensure data is always available for investigation and improving flight safety.

When an airplane crash occurs, flight recorders become the golden key that helps experts track down the cause of the incident. However, only those in the official investigation team such as the NTSB, FAA and other competent authorities are allowed to access the data collected from these devices.

According to electrical engineer Houbing Song from the University of Maryland (USA), who participated in developing the recording system for the FAA, analyzing data from the black box is "no different from a criminal investigation", where every detail can be vital evidence.

Unlike older generations that used magnetic tape, modern flight recorders store data on solid-state memory cards, similar to the memory cards in laptops or phones.

The first phase of the recovery process will check that the memory card is intact, then back up the entire contents for analysis. Depending on the severity and complexity of the accident, the investigation can take anywhere from several weeks to several years.

In addition to post-accident investigations, flight data recorders provide significant value in day-to-day operations. Many commercial airlines are now participating in a voluntary program called Flight Operations Quality Assurance (FOQA), which works with the FAA to download portions of their flight data for analysis, monitoring, and performance improvement.

For example, the FAA could use this data to detect fuel consumption problems, potential engine failures, or other inefficient operating behaviors.

“The idea is to spot and address dangerous trends before they lead to serious incidents,” says expert David Esser.

However, a major weakness of the black box is that it can only be accessed after the flight. In situations where the device is severely damaged or cannot be found, data recovery may become impossible.

To overcome this limitation, there are now initiatives aimed at transmitting real-time data from flight data recorders to the ground. "The technology is there. It's just a matter of when we decide to deploy it," Esser said.