The importance of black boxes in resolving aircraft accidents is undeniable. So why do we still face unresolved mysteries?

At 1:49 a.m. Universal Time on June 1, 2009, the pilots of Air France Flight 447, en route from Rio de Janeiro to Paris, communicated with Brazilian air traffic control as they exited their airspace. They were about to enter a communications black hole over the South Atlantic Ocean, where it would take two hours before they could reach anyone on the ground again. For the experienced captain of the Airbus A330, this routine handoff was typical. Despite the impending thunderstorm, nothing indicated any issues. "Air France four-four-seven, contact Atlantic center," the captain confirmed before leaving the cockpit for a scheduled rest—standard practice on this lengthy 11-hour flight. A relief pilot took over with the copilot at the controls.

Those were the final communications from the cockpit, and the 228 passengers and crew aboard would not reach their destination. Two years later, however, a team that previously discovered the Titanic managed to recover two metal boxes from the wreckage at a depth of 13,000 feet in the ocean. If the recordings inside had withstood the harsh conditions of the ocean floor, they could unravel the mystery of Flight 447's fate.

The search thus far had been one of the largest and most expensive in airline accident history, costing over $30 million. This latest endeavor employed autonomous submersibles to scour the ocean floor, marking what would be the final attempt before authorities considered halting further costly underwater investigations.

Contrary to what their name suggests, black boxes are actually orange, designed for easy discovery. They are incredibly durable, built to endure fires reaching 2,000 degrees Fahrenheit and impacts equivalent to 3,400 times Earth's gravitational force, roughly the speed of 310 mph. (Humans can typically tolerate about 5 Gs before losing consciousness.) Inside these boxes is vital information detailing the plane's last moments. Remarkably, they had never been retrieved after such prolonged submersion in extreme depths. Upon their arrival under police protection at a laboratory in Paris, investigators quickly discovered that, aside from some minor damage, the data within was intact.

By May 2011, the final moments of the Air France flights had come to light, unveiling a sequence of events, each of which could have been avoided, but ultimately led to a tragic crash. Initially, a cloud of ice pellets struck the aircraft, freezing its speed sensors, known as pitot tubes. The cockpit erupted with loud alarms, sending the pilots into a state of panic. A minute later, the alarms ceased when a backup speedometer system activated. However, the copilot had tilted the Airbus 330 upward, causing it to stall, and he spent the last moments of the flight trying to raise the nose, counter to standard pilot training. The aircraft plummeted at an alarming rate of 12,000 feet per minute. Just before impact, the transcript revealed the pilots were still struggling to comprehend their situation, with one pilot exclaiming, "[expletive] we’re going to crash! It’s not true! This can’t be happening!" The final recorded words were, "We’re dead."

The conclusion pointed towards pilot error, but the reality was more complex. “It was just mind-boggling,” remarked David Learmount, a former British air force pilot and aviation safety expert. How could skilled pilots, operating a cutting-edge aircraft for a prestigious airline, make such a fundamental error? One disturbing theory suggested that pilots flying modern ‘fly-by-wire’ jets, where much of the flying is managed by computers, were simply unprepared to manually fly the plane and recover from a stall at cruising altitude.

This incident served as a critical alert to the airline industry about the perils of excessive dependence on automation. The information extracted from the black boxes prompted the industry to implement new global training protocols for pilots on managing emergencies at 35,000 feet, including how to address high-altitude stalls.

The recovery of the AF 447 black boxes marked a significant triumph in the realm of aircraft crash investigations. However, for many observers, it highlighted the shortcomings of existing technology. Why was it so challenging to locate the plane? Black boxes are equipped with underwater locator beacons that activate automatically and emit a signal once per second, detectable by sonar—but only for a mere 30 days. Then arises a larger question: In a world where cellphones can track our location globally, why aren’t we transmitting flight data in real-time? This query has haunted the aviation industry ever since.

The development of the first black box flight recorder—an essential device on every civilian airliner since the 1960s—stems directly from the failures of another aviation milestone. The British De Havilland Comet was the first jetliner to enter commercial service in 1952, but soon after, several of these aircraft mysteriously crashed. As the incidents increased, pilots and aviation experts united to uncover the underlying causes.

Among these experts was David Warren, an Australian research scientist who worked on fuel tank designs at a government aeronautical research facility in Melbourne. Growing up in the remote Northern Territory, he was the son of missionaries. The aviation industry in Australia was still in its early stages, and in 1934, when Warren was just nine years old, his father died in a small propeller plane accident while traveling to his new parish in Sydney. Although Warren—who passed away at 85 in 2010—claimed that this personal tragedy did not influence his drive to create a crucial aviation safety tool, it undeniably highlighted the dangers of early aviation.

Warren was also passionate about radio technology. In 1953, while contributing to a scientific panel investigating the Comet crashes, he encountered a German invention at a trade fair. Known as the "Minifon," it was marketed as the first pocket recorder and closely resembled a modern Sony Walkman. Recognizing the potential for this small device to enhance aviation safety, he later recounted, "The idea struck me after a major Comet crash in 1953. It happened without any clear reason, without witnesses, and with no survivors—truly a perplexing mystery.

After observing the miniature recorder, I combined these concepts in my mind. I thought, ‘If a businessman had used one of these devices on the plane and we could recover it from the wreckage, we could replay it and uncover the cause of the crash.’

While this might be considered the pivotal moment in the black box narrative, Warren's supervisor was not impressed. Years later, he shared with a BBC interviewer, "I was instructed to focus on blowing up fuel tanks and to pass my idea to someone else." However, Warren persevered and eventually secured more backing to create a prototype, which he presented to Australian authorities in 1958, only to face harsh criticism. One reaction was, "This recorder will produce more expletives than explanations."

Warren’s invention might have languished in obscurity if not for a fortunate meeting with the U.K.'s leading aviation official. During a visit to Warren's laboratory, the official recognized the significance of the prototype. He arranged for Warren to fly to England, where he demonstrated the device to a much more receptive audience than he had experienced back home. A British manufacturer quickly acquired the rights, but it would still take nearly a decade before these devices became mandatory for flights in major aviation countries. Warren was not alone in his efforts; during and after World War II, other devices aimed at capturing flight data, such as airspeed and altitude, were already under development. In the U.S., a University of Minnesota engineering professor, James Ryan, patented a flight recording device in 1953, although it lacked the capability to record cockpit conversations.

According to Sean Payne, an accident investigator with the National Transportation Safety Board who has researched the history of flight recorders, the fundamental idea of capturing flight data dates back to the Wright brothers. "They apparently used a clock to record the propeller's revolutions per minute during their first flight," he noted. However, it is Warren who is credited with the concept of installing a cockpit voice recorder in an aircraft.

At the same time, unresolved aviation accidents continued to diminish public trust in air travel. The De Havilland Comet was grounded in 1954 after two more fatal incidents—three crashes within 12 months—ultimately leading to its retirement from commercial service years later. Investigators found that cracks in the fuselage due to metal fatigue had caused the jets to explode mid-flight. Despite initial resistance to the idea, Australian authorities finally mandated the installation of both data and voice recorders in all aircraft following yet another tragic air crash in 1960, making them the first in the world to do so. The United States followed suit in 1964, and by 1967, nearly all aircraft operating in the U.S. and most major aviation nations were equipped with these devices.

The first commercial model was produced by the British company S. Davall & Sons and was nicknamed the "red egg" due to its round shape and bright red color, which helped in locating it at crash sites. Since then, all black boxes, regardless of their origin, are encased in a bright hue known as "safety orange" for visibility. However, the term "black box" became popular as pilot slang for electronic equipment. The earliest models were quite basic, relying on foil or magnetic tapes that produced unreliable sound quality and limited measurements of parameters like speed and altitude. It wasn’t until decades later, in the 1990s, that solid-state recorders with more robust memory boards were introduced, although older aircraft still utilize analog models. NTSB’s Payne mentions that he sometimes encounters those vintage models in crash investigations worldwide.

Black boxes quickly demonstrated their resilience and essential value. Beyond the case of flight AF 447, numerous other aviation disasters saw these devices survive harsh conditions, providing crucial data. For instance, after TWA Flight 800 exploded over Long Island Sound just 12 minutes after departing JFK in 1996, initial suspicions pointed to terrorism or fire from nearby military aircraft. However, gaps in the cockpit voice recorder ultimately clarified the incident: a spark ignited nearly empty fuel, causing a fire that cut off power to the recorders just before the aircraft disintegrated. "The cockpit voice recorder sometimes reveals more by what it omits," states Christine Negroni, an air crash investigator and author of *The Crash Detectives*.

A similar situation unfolded in 1988 when Pan Am Flight 103, carrying 259 passengers and crew, detonated over Lockerbie, Scotland, just days before Christmas. The recovered voice recorder offered a vital clue by continuing to record for a brief moment after the power was lost, capturing the sound of the bomb that had been concealed in the aircraft's cargo area. More recently, the black boxes retrieved after the crashes of Lion Air Flight 610 in October 2018 and Ethiopian Airlines Flight 302 in March 2019 revealed that flight control software, which repeatedly forced the nose of the Boeing 737 MAX down, contributed to both tragedies, prompting the FAA to mandate software updates from Boeing.

Commonly referred to as the "black box," this crucial device actually consists of two components: the cockpit voice recorder (CVR) and the flight data recorder (FDR). The CVR captures sounds in the cockpit, using microphones placed in the pilots’ headsets and the cockpit center, recording up to the last two hours of a flight before being overwritten by the next one unless needed for an investigation. The FDR collects a wide range of parameters, including speed, altitude, and outside temperature, using sensors located throughout the aircraft. The Federal Aviation Administration mandates that commercial airplanes record a minimum of "11 to 29 parameters," depending on size. Each unit typically weighs between 10 to 15 pounds. To illustrate their functions: while the FDR indicates what happened, the CVR provides insight into why it occurred, emphasizing the human factor, as noted by Payne. Furthermore, these boxes appeal to airlines due to their long lifespan—up to 30 years—minimal maintenance requirements, and relative affordability, generally costing under $20,000 each.

Housed in protective titanium or steel casings, the recorders are located in the tail of the aircraft for optimal safety. As planes usually crash nose-first, this positioning helps shield them from damage. Before installation, the recorders undergo rigorous testing. For example, the crucial cylinder containing the memory boards is propelled from an air cannon and smashed into a target. It also endures a 500-pound weight dropped from a height of 10 feet. Researchers challenge the FDR by crushing it, exposing it to flames, soaking it in jet fuel, and submerging it in pressurized saltwater tanks to ensure it can emit signals even from 20,000 feet underwater. Such preparation is clearly effective: no recovered black box has ever been so damaged that it failed to provide usable data.

When retrieved from accident sites, the boxes, despite their durability, require careful handling. A team of specialists places them into secure containers, sometimes under police protection, as was the case with AF 447. In underwater incidents, the boxes are stored in water-filled coolers to protect them from air until they reach specialized labs for data downloading and analysis, a process that can take several months. Not all countries have the necessary facilities, so in some instances, the boxes are shipped thousands of miles to leading labs in the U.S., France, and other locations. Experts—including airline representatives, aircraft manufacturers, and NTSB specialists—gather to examine the data, with comprehensive investigations typically taking around 18 months to complete.

While black boxes are known for their durability and cost efficiency, they do have notable limitations. The most significant of these is the time and expense involved in retrieving the devices, which could potentially be minimized if the industry adopted a system allowing for data transmission from black boxes to satellites during flight.

Although the technology is available, the airline industry—concerned about the costs and the need to completely revamp current systems to accommodate the streaming of large data volumes—has been slow to adopt it. Experts in the field argue that because fatal crashes are infrequent, it boils down to a cost-benefit analysis. However, there are initiatives underway to encourage progress: The International Civil Aviation Organization (ICAO) has mandated that by the end of 2023, airlines must show that they are prepared for the "timely recovery of flight data" from aircraft.

Another driving factor is the fact that nearly 10 years have passed since Malaysia Airlines Flight 370 vanished from radar while en route from Kuala Lumpur to Beijing on March 8, 2014, as it entered Vietnamese airspace. The Boeing 777 and its 239 passengers have never been located, leaving MH 370 as one of the most significant unsolved mysteries in aviation history.

This incident is one of the motivations behind Honeywell's proposal for a "black box in the sky," which supports the idea of live-streaming data from aircraft to ground stations through a network of satellites. Additionally, there are calls for underwater locators to have longer battery lives and broader operational ranges; some experts are even advocating for a backup recording device that would eject from the aircraft prior to impact.

There is growing momentum within the industry to extend the duration of recorded data. The NTSB supports the initiative for 25-hour cockpit voice recordings, aligning with the flight data recorders that collect readings for the same period, a standard already implemented by European countries. Additionally, a proposal to install cameras in the cockpit would serve as a further safeguard.

However, there has been strong resistance from pilots regarding privacy concerns, reminiscent of the pushback David Warren faced around 70 years ago when he began developing the first CVR. Warren expressed understanding of these concerns, stating, “Initially, it feels like Big Brother is listening. But once pilots realize that this recording is deleted right after the flight, they begin to accept it.”

Many pilots recognize that the introduction of black boxes has significantly enhanced their safety. John Cox, a U.S. airline pilot and head of an aviation safety consultancy, emphasizes this impact: “The significance of this advancement cannot be overstated. It provided us with objective data that cannot be overlooked.”

If all necessary data is streamed in real time, could this signify the end of the black box as we currently know it? NTSB’s Payne suggests that while this may happen eventually, it is not imminent. For now, having a set of black boxes on every aircraft serves as an effective backup system and contributes to the safety of commercial aviation. “Among other advantages, airlines can analyze data from each successfully landed flight to detect issues before they escalate into tragedies,” Payne notes. According to recent statistics, 2022 marked one of the safest years in commercial aviation history, with only five fatal accidents out of 32.2 million flights.

Some experts, including former NTSB member and aviation safety consultant John Goglia, argue that black box technology has proven so effective—and the rare occasions it has failed are so few—that the industry should refrain from rushing to overhaul it. “The data we've received has been instrumental in solving nearly every accident, anywhere in the world,” he asserts. “That’s an impressive track record.”