How Black Boxes Operate

In Indonesia, divers successfully recovered one of the flight data recorders from the Lion Air jet that crashed into the Java Sea on October 29, 2018, killing 189 people. According to reports from AP, the flight data recorder is expected to assist investigators in uncovering the cause of the crash involving the two-month-old Boeing 737 MAX 8, which occurred just after takeoff. The cockpit voice recorder will also provide valuable audio, including the crew's communications, engine sounds, warning signals, and other flight sounds.

When an airplane crashes, numerous questions often remain unanswered. That's why investigators rely on flight data recorders (FDR) and cockpit voice recorders (CVR), or "black boxes," to uncover the truth. After any airplane accident in the U.S., the National Transportation Safety Board (NTSB) immediately begins a search for the aircraft's black boxes to assist in the investigation.

Unfortunately, answers don't always arrive quickly. Investigators took almost two years to recover the black box from Air France Flight 447, which crashed into the South Atlantic Ocean on June 1, 2009. Despite the crash, the black box survived both the impact and being submerged under nearly 13,000 feet of salty, corrosive seawater. Ultimately, the data confirmed that pilot error contributed to a stall, which led to the crash.

These recording devices, priced between $10,000 and $15,000 each, capture crucial details of the moments leading up to an accident. In this article, we explore the two types of black boxes, how they withstand crashes, and the processes involved in retrieving and analyzing them.

Black Boxes Begin

The adoption of aviation recorders became widespread only after World War II. Since then, the technology of black boxes has advanced significantly, allowing for the collection of far more detailed data about an aircraft's operation.

In the early days, black boxes used magnetic tape, which emerged in the 1960s. This system functioned much like a standard tape recorder, with Mylar tape moving over an electromagnetic head that recorded the data. Today, black boxes rely on solid-state memory boards, a technology that gained prominence in the 1990s.

Solid-state recorders are much more reliable than their magnetic tape predecessors. Solid-state technology employs stacked memory chip arrays, eliminating moving parts. This absence of moving parts reduces the likelihood of maintenance issues and the risk of failure in the event of a crash.

Both the CVR and FDR store data on stacked memory boards inside the crash-survivable memory unit (CSMU). These memory boards offer enough storage to hold two hours of audio data for CVRs and up to 25 hours of flight data for FDRs.

Aircraft are outfitted with sensors that capture various data points such as acceleration, airspeed, altitude, flap settings, external temperature, engine performance, and cabin conditions. While magnetic-tape recorders can monitor around 100 parameters, solid-state recorders can track far more.

Take the Boeing 787, for example, which is capable of recording an astounding 146,000 parameters, generating multiple terabytes of data from just one flight. While this massive data collection is valuable for aircraft monitoring, it can also be overwhelming for engineers and maintenance teams. To cope with this deluge, advanced data management software is essential.

Regardless of whether the system is old or up-to-date, all the data from the airplane's sensors is transmitted to the flight-data acquisition unit (FDAU), typically located in the electronic equipment bay beneath the cockpit. Acting as the key intermediary, the FDAU processes sensor data before passing it on to the black boxes.

Both black boxes are powered by two distinct generators sourced from the plane's engines. One provides a 28-volt DC power supply, while the other delivers a 115-volt, 400-hertz (Hz) AC power output.

Cockpit Voice Recorders

Almost every commercial airplane features several microphones in the cockpit designed to capture conversations among the flight crew. These microphones also record ambient sounds within the cockpit, such as the activation of switches or any unusual sounds like knocks or thuds. Typically, the cockpit is equipped with up to four microphones, all linked to the cockpit voice recorder (CVR).

The microphones transmit their audio signals to the CVR, where the sounds are digitized and saved. Additionally, the cockpit contains an associated control unit, which amplifies the audio signals before they are recorded by the CVR. The four microphones are positioned on the pilot's headset, co-pilot's headset, a third crew member's headset (if applicable), and one located centrally in the cockpit to capture alarms and other background noises.

Magnetic-tape CVRs typically record the last 30 minutes of audio. They operate on a continuous loop of tape, which refreshes every 30 minutes, erasing older recordings as new data is captured. Solid-state CVRs, on the other hand, can store up to two hours of audio and function similarly by overwriting old recordings with new ones.

Flight Data Recorders

The flight data recorder (FDR) is responsible for capturing the operational data from an aircraft's systems. Various sensors are connected to the flight-data acquisition unit, which then transmits the information to the FDR, ensuring that every action of the pilot is logged.

In the U.S., the Federal Aviation Administration (FAA) mandates that airlines record a minimum of 11 to 29 parameters, depending on the aircraft size. Magnetic-tape systems can store up to 100 parameters, while modern solid-state FDRs have the capability to record hundreds or even thousands more.

On July 17, 1997, the FAA introduced a regulation in the Code of Federal Regulations that necessitates recording at least 88 parameters for aircraft built after August 19, 2002. Below are some of the key parameters recorded by most FDRs:

Solid-state recorders are capable of tracking a broader range of parameters compared to magnetic tape, as they facilitate a quicker data transfer rate. Solid-state flight data recorders (FDRs) are capable of storing up to 25 hours of flight data. Recording additional parameters provides investigators with more insights into the possible causes of an accident.

Designed for Durability

Airplane crashes are often catastrophic events. In many of these incidents, the only components that manage to survive are the crash-survivable memory units (CSMUs) found within the flight data recorders and cockpit voice recorders. Typically, the chassis and internal parts of the recorders are severely damaged. The CSMU is a large cylindrical device that attaches to the flat part of the recorder. It is specifically designed to endure extreme temperatures, violent crashes, and immense pressure. In older models using magnetic tape, the CSMU is housed inside a rectangular casing.

The CSMU in a solid-state black box is constructed with three layers of materials to insulate and protect the stack of memory boards that store the digitized data.

Let’s take a closer look at the materials that form the protective barriers for the memory boards, starting from the innermost layer and moving outward:

These reinforced enclosures play a crucial role. Without sufficient protection, all of the flight data would be lost. To ensure the data remains intact, engineers subject their black boxes to rigorous testing, subjecting them to extreme conditions to verify their durability.

Testing the Durability of a Crash Survivable Memory Unit

To guarantee the reliability and crash-resilience of black boxes, manufacturers rigorously test the CSMUs. Remember, only the CSMU must endure a crash — if investigators retrieve this, they can access the critical information. To test the unit, engineers load sample data onto the memory boards in the CSMU. Afterward, they check the readout to see if any data was corrupted by impact, heat, or pressure from the crash.

There are various tests involved in the crash-survival sequence:

During the fire test, the memory interface cable connecting the memory boards to the circuit board is burned away. Once the unit cools, researchers disassemble it, retrieve the memory module, and restack the memory boards. They then install a new memory interface cable and reconnect the unit to a readout system to confirm that all the preloaded data is intact.

Black boxes are typically purchased directly from airplane manufacturers and installed by them. Both recorders are positioned in the tail section of the aircraft, as this location enhances their chances of surviving an accident. The exact placement of the recorders varies by aircraft model. Sometimes they are found in the galley's ceiling, the aft cargo hold, or within the tail cone that covers the rear of the plane.

Post-Crash Procedures

Despite being called "black boxes," aviation recorders are actually painted bright orange. This vivid color, combined with reflective tape on the recorders' surfaces, aids investigators in locating the black boxes after an accident. These features are particularly useful when a plane crashes into water. There are two potential reasons for the term black box: One theory suggests it stems from early recorders being painted black, while the other proposes it refers to the charring that happens in fires following an accident.

Black boxes, in addition to their paint and reflective tape, are fitted with an underwater locator beacon (ULB). If you observe a black box closely, you'll typically notice a small cylindrical object attached to one end. While it serves as a handle for carrying, this cylinder is primarily a beacon.

When a plane crashes into the water, the beacon emits an ultrasonic pulse that is inaudible to humans but easily detected by sonar and acoustic devices. A submergence sensor, shaped like a bull's-eye, activates the beacon when it comes into contact with water.

The beacon operates at a frequency of 37.5 kilohertz (kHz), and its sound can travel as deep as 14,000 feet (4,267 meters). Once activated, it emits a pulse every second for 30 days. Powered by a battery with a six-year shelf life, the beacon may occasionally break off in a severe impact collision.

In the U.S., when a black box is found, it is sent to the National Transportation Safety Board (NTSB) labs. Every effort is made to transport these devices carefully to avoid further damage to their recording medium. In water-related accidents, the recorders are placed in a cooler of water to prevent them from drying out.

Retrieving Information

Once the black boxes are located, investigators transfer the recorders to a lab where they can download the data and attempt to reconstruct the accident’s sequence of events. This analysis process can span several weeks or months. In the United States, manufacturers of black boxes provide the National Transportation Safety Board with the systems and software necessary to fully analyze the recorded data.

If the Flight Data Recorder (FDR) remains undamaged, investigators can replay the data directly from the recorder by connecting it to a readout system. With modern solid-state recorders, data can often be extracted in minutes via USB or Ethernet ports. Frequently, recorders found in wreckage may be dented or burned. In such cases, the memory boards are removed, cleaned, and fitted with a new memory interface cable. The memory board is then linked to a working recorder, which uses specialized software to recover the data without risk of overwriting it.

A specialized team of experts is usually called in to interpret the recordings on a Cockpit Voice Recorder (CVR). This group typically includes representatives from the airline, the airplane manufacturer, an NTSB transportation safety expert, and an NTSB air safety investigator. It may also involve a language specialist from the FBI and, if necessary, an interpreter. The team’s task is to analyze 30 minutes of recordings from the CVR, a process that is meticulous and can take several weeks to complete.

Both the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) are essential tools in any aircraft investigation. These devices are often the only components to survive an aircraft crash, providing vital insights that would be impossible to gather in any other way. As technology advances, black boxes will continue to play a key role in accident investigations.

The Future of Black Boxes

There are many possible advancements on the horizon for black box technology. A major gap in current systems is their inability to record video of cockpit activity. For years, the National Transportation Safety Board has tried unsuccessfully to add video capabilities to black boxes. However, many pilots oppose the idea, arguing that such systems would violate their privacy, and that the current data capture is already sufficient for accident investigations.

The NTSB firmly believes that more data is always better when it comes to investigating plane crashes. For now, however, video recording remains suspended in these investigations.

The technology, on the other hand, is fully equipped. Airbus, for example, installs the Vision 1000 system in all its helicopters. Positioned behind the pilot, the Vision 1000 camera captures both the pilot’s actions and the cockpit, as well as the view ahead through the windshield, recording at a rate of four frames per second. It weighs only half a pound and needs just power and a GPS connection to operate.

Video is not the only advancement that has faced resistance from traditionalists. Since 2002, certain lawmakers have backed the Save Aviation and Flight Enhancement Act, which would mandate two flight recorders, one of which would automatically eject during an incident. These self-ejecting recorders are easier to find and far less likely to suffer catastrophic damage. However, the bill has yet to pass Congress.

Black boxes are not exclusive to aircraft—they are now a common feature in many types of vehicles. You might even have one in your car without realizing it. Around 90 percent of new vehicles are equipped with Event Data Recorders (EDRs), which capture the same kind of data as airplane black boxes. Though primarily designed to oversee the vehicle's safety systems, EDR data is often used by investigators to analyze accidents and, in some cases, to assign responsibility.

When it comes to airplane black boxes, there is a possibility they might soon be phased out. Rather than recording data to a physical device, airplanes could begin streaming their essential data directly to a ground-based station. These systems already exist, such as AeroMechanical Services’ FlyhtStream, which transmits flight data to a central base via satellite.

These systems eliminate the frantic search for a black box that may have been destroyed in the crash, and they might also prove to be more reliable. However, for now, black boxes remain an essential tool, as thousands of flights take off every day, carrying millions of passengers around the globe.