Question: With all the aviation mishaps lately, I’ve been wondering about these “black box flight data recorders” the media talks about. I realize they can help determine why a crash happened. But how can they survive a crash, especially one where the plane sinks in the ocean or burns. — Wary Traveler, San Diego, CA
Answer: They call them “black boxes” but as you can see from the NTSB photo, this is a misnomer. When they were first developed, back in the 1930s–1940s, flight data recorders (FDRs) were indeed black — it helped with heat dissipation in these totally sealed devices. Advancements in materials science and technology ultimately allowed them to be painted bright orange for visibility during recovery. They use a special high-temperature paint that reflects heat and doesn’t blacken when exposed to flames.
FDRs have been required for commercial aircraft in the United States since 1967. Small private aircraft (like the popular Cessna 172) are exempt from this requirement — regulations only mandate an Emergency Locator Transmitter (ELT). However, modern small aircraft with digital cockpit displays have built-in data logging functions and can act as an FDR. Many private pilots also use their own portable recording devices, such as action cameras wired into their intercom systems. They can assist with training or when diagnosing an incident, but they are not a regulatory requirement.
There are two types of flight recording devices: the FDR preserves the recent history of the flight by recording dozens of parameters collected several times per second; the cockpit voice recorder (CVR) preserves the recent history of the sounds in the cockpit, including the words of the pilots. The two devices may be combined into a single unit. The technology must meet several rigorous standards:
- They are required to withstand an impact of 3400 g (340X the force of gravity),
- survive temperatures over 1,000 °C (1,830 °F) for at least 60 seconds,
- and include an automatically activated underwater locator beacon that can produce a signal for up to 30 days at depths of up to 20,000 ft.
In addition to the special paint mentioned earlier, black box memory components (these days mostly SSHDs) are encapsulated in fire-resistant insulation. This assembly is surrounded by a corrosion-resistant housing of stainless steel or titanium, weighing in at only 10 pounds. They cost between $10,000 and $15,000 each but last some 30 years. The data they hold is invaluable to investigators for determining the chain of events leading up to an accident. Current generation solid-state recorders can capture thousands of flight parameters, withstand more severe accidents, and store up to 25 hours of continuous flight data.
Less than 10% of all black boxes have been unrecoverable — physically lost in mid-air explosions or crashes at sea or in rugged terrain. Never has a recovered black box been so badly damaged that it yielded no usable data. These things are built to survive.
There’s a meme going around that’s worth comment: Why don’t they build airplanes out of the same stuff they use for black boxes? The question is not posed rhetorically. The answer is simple: The airplane would weigh too much. The less your airplane weighs, the easier it is to fly.
The normal weight of a commercial 747 airliner is around 750,000 pounds. If you swapped out its aluminum fuselage and skin with black box level titanium, the aircraft would weigh 1,260,000 pounds. With stainless steel it would weigh 2,150,000 pounds. That’s a tough lift even with larger wings and more engines — all of which also add weight. And before you ask, the same weight issues would apply to black box automobiles.
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