The Lava-Proof Box Aviation Couldn’t Do Without

Designed to withstand temperatures of over 1000 degrees C and the weight of a rhino, black boxes have assisted air crash investigators for the last 50 years. But, as Thomas Haynes discovers, their future could be even more impressive…

Is there an object on earth that can survive as much punishment as a black box flight recorder?

The testing requirements are some of the most extreme and stringent on earth. Firstly, the systems inside are covered by a fireproof box that is certified to withstand 1,100°C (2,012°F) for 30 minutes – that’s almost exactly the temperature of lava.

Black boxes can withstand 1,100°C - almost exactly the same temperature as lava. United States Geological Service

Following this, the black boxes must then survive a sustained 260°C (500°F) heat for ten hours – that’s basically the maximum temperature that the oven in your kitchen can go to.

Black Boxes
Black boxes, as they're widely known, are actually not painted black, but instead a bright orange colour. Wikimedia Commons/YSSYguy

But this is just the start. Black boxes can also handle a static crush force of 2.2 tonnes (5,000lbs) for five minutes on each of their six sides – that’s pretty much the weight of a Range Rover. The penetration resistance test then involves a 226kg (500lb), 2.5cm (0.25in) spike that’s dropped from 3m (10ft).

Flight recorders can withstand a static crush force equivalent to the average weight of a white rhino. Flickr Commons/Bernard Spragg

And with around 70% of the world covered by water, it’s surprising to note that the boxes themselves are not airtight, so water will enter the enclosure when it is submerged. The memory boards, however, are often given special protective coatings to stop corrosion.  

Black boxes are also accredited to survive 20,000ft (6000m) of water pressure for a 24-hour period. At that depth, for each square centimetre of the box’s surface, 611kg of force is being applied.


The black box recorders’ ability to survive a crash is one of their most important characteristics, and these ingeniously robust objects have been assisting air crash investigators for at least the last 50 years. When an aircraft incident occurs, finding out how it happened and what caused it, is a critical process. Discovering how an event transpired means that regulators and manufacturers can make sure a similar incident doesn’t happen again, and black boxes are one of the most valuable tools investigators have at their disposal to identify the complex chain of events that always precedes an accident.

These small devices have an intriguing past, and an equally fascinating future. The concept of recording flight data and cockpit voices has been around for more than 60 years, but in that time, the developments have been fairly minor in nature.

David Warren
David Warren, an Australian inventor, is widely credited with conceiving the first flight data recorder. Public Domain

Flight recorders are commonly split into two types: a flight data recorder (FDR) and a cockpit voice recorder (CVR). The latter’s role is in its name, as it captures the audio from the flight deck, while the FDR logs thousands of data points for a range of parameters every second.  

In the beginning, there were two competing designs – one from Australia and the other from the United States – both of which followed the same principles. They each wanted to record the flight data to assist investigators.

Conceived in 1953, the Australian device – which was invented by David Warren – was popular in the UK when the British Air Registration Board (the Civil Aviation Authority’s predecessor) realised the significance of the invention in aiding its investigations. During the same year, Professor James Ryan – the inventor of retractable seat belts for cars – applied for a “Flight Recorder” patent in the US. A “cockpit sound recorder” was independently realised in the country in 1961.


While the job flight recorders do hasn’t changed very much over the years, the way in which they capture and store the data has. Advancements in technology have led to changes in storage medium and the amount of information these devices can hold.

Mark Ford has spent more than 30 years working with flight recorders both at a major British airline and now as a senior investigator specialising in data recording systems for the UK’s Air Accidents Investigation Branch (AAIB). “In the 1960s when the first recorders started appearing on aircraft, they used some very old technology and were recording a limited number of parameters,” he says. “They scratched the data onto a metal foil that lasted about 200 hours before engineers had to replace the cartridges.”

The progression to magnetic tape from metal foil recorders was made in the 1970s. Flickr Commons/7263255

Throughout the 1970s, the technology moved to recycling (re-writable) recorders and then in the next decade, the progression to magnetic tape was realised. The Boeing 747-100, Lockheed L-1011 TriStar and the BAC One-Eleven all featured recycling recorders, negating the need to replace the cartridges.

Delta Air Lines
The Lockheed L-1011 TriStar was one of the first types to feature a recycling (re-writeable) recorder. Flickr Commons/Aero Icarus

“Through the 1990s we started to see the introduction of solid-state recorders with memory akin to what you would have in a USB flash stick,” Ford recalls. “But because of the shear cost of memory, the earliest recorders only had about 2MB of storage, but they could still fit 25 hours of recorded flight data.”

The development of the CVR followed much of the same path as the FDR. The transition between storage mediums was the same but slightly slower than the data recorder, moving to solid state because of the aforementioned memory limits.

Solid State Storage
From the 1990s onwards, recorders made the transition to solid state storage. NTSB

Presently, the requirements for the CVR is that it records the last two hours of each flight. In the near future, this is set to expand to come in line with the FDR at 25 hours.

The Leap to Live Streaming

The aviation industry is one of those sectors within which change usually occurs in response to regulatory mandates or guidelines. An example of this is the CVR recording time extension, which comes as a result of a European Union Aviation Safety Agency (EASA) mandate.

A separate regulatory directive covers the future requirement for all flight recorders to be able to allow for the “timely recovery of data”. The mandate doesn’t specify how this is to be done, it just states that the retrieval of information needs to be completed in a timely manner.

A company at the forefront of combatting this challenge is Honeywell Aerospace. The Arizona-based firm is no stranger to developing and manufacturing flight recorders as they’ve been doing it for more than 60 years, and are now on their sixth generation of the devices.

Honeywell Aerospace
Amanda King (left) and Borka Vlacic (right) from Honeywell Aerospace.

Borka Vlacic, director of marketing and product management for satellite communications at Honeywell Aerospace, said: “We are very well recognised by the industry as a leader for black boxes for all commercial aviation. We have also been involved in developing industry standards for a long period of time too.”

Amanda King, vice president/general manager of Aerospace Connected Secure Solutions, added: “Honeywell is on all the narrowbody aircraft and most of the widebodies; the designs we made previously and the ones we’re developing for the future are easy to upgrade. We make the form and fit the same… and this is how we secure our position on so many aircraft like we are today.”

Honeywell Devices
Honeywell makes its recorders' form and fit the same to allow for an easy upgrade process. Honeywell Aerospace

The next big step in the development of flight recorders comes in the form of connected variants. Honeywell is currently in the process of creating devices that are linked to the cloud through satellite communications. These systems are being designed to satisfy the EASA “timely recovery” mandate, which is due to come into effect in 2023.

“When you think about timely recovery of data, how do you get that with something that’s flying at 30,000ft?” asks King. “There are a few interesting options, but the most logical one to us was to leverage the satellite communication capabilities that we have and integrate that into our recorders.”

Honeywell Infographic
An infographic showing how Honeywell's new HCR25 connected flight recorders will work. Honeywell Aerospace

The technology to allow connected black boxes to function has been around for quite some time, however, the cost was uneconomic until recently. “With the increase in the use of satellite communication, bandwidth became wider, transmission and installation costs also dropped. All that boom and development allowed something to happen and made it possible and accessible,” explains Vlacic.

Honeywell is working with satellite operator and long-time partner, Inmarsat, to bring this next generation set of devices to the market. Called the Honeywell Connected Recorder (HCR-25), the system will enable flight data and cockpit voices to be streamed live via a satellite to a secure facility on the ground, reducing the urgency to find the boxes when an incident occurs.

Honeywell Aerospace
The HCR-25 FDR looks almost identical to previous generation devices. Honeywell Aerospace

There are a number of options to do with what data, and how much of it is transferred live from the aircraft. The first and simplest is the live transmission of everything in real-time; the downside to this, of course, is that this will use the most bandwidth.

The second option is a condition-based set-up which would transmit certain parameters if a predetermined event were detected. This choice would limit the total bandwidth requirements for the device.

Honeywell's HCR-25 CVRs will satisfy the EASA mandate to record 25 hours of audio that comes into effect next year. Honeywell Aerospace

“Flight has core parameters – airspeed, attitude, altitude and another subset of things that are also important – and if anything were to go outside the limits the system could trigger something that would then start auto streaming, so we don’t have to use the bandwidth 100% of the time but we want it when we need it,” King says.

Traditional Recovery

When an aircraft accident occurs, the black boxes are always the items we’re always waiting to be found. But how do investigators find them, and what tools do they have available?

Currently most recorders in service are fitted with underwater locator beacons. Prior to the MH370 and Air France 447 crashes, the requirement was for a high frequency beacon at 37.5khz that would last 30 days. Following these crashes, it was extended to 90 days.

The black, vertically mounted cylindrical object in this image is the underwater beacon. Honeywell Aerospace

“The rationale behind that is that if you have an aircraft crash inshore, you should be able to find it reasonably quickly, but as we know, if something is a long way offshore, it takes a lot of time to get the ships which are required to search deep waters in place,” says Ford.

These beacons have relatively short ranges, depending on the sea-state, that may only extend to 2nm (3.7km). If the aircraft is deep, says Ford, they use underwater hydrophones to locate the devices.

The AAIB tows the equipment behind a boat at roughly 4kts (5mph) along a racetrack-type pattern up and down at 1500m (5,000ft) spacing. Investigators are then listening for an audible tone, which indicates the presence of the recorders.

On some aircraft that fly over water, there is also now a set of recorders that have a low frequency beacon that transmits at 8.8khz. The benefit of this option over its higher frequency counterpart is that it provides much better range, topping out at around 10nm (18km).

“The idea is that you would use this to home in on the approximate location and then use the high frequency beacon which will give you better direction. One we’ve identified the area of the wreckage we have equipment that divers can go down with to use to home in on the recorders,” Ford said.

If the sea is too deep then investigators send down remotely operated vehicles. The ROV pictured is being used by the US' National Transportation Safety Board (NTSB). US Department of Defense

If the crash has occurred in a location where the water is deeper than is allowed for divers, the organisation uses remotely operated vehicles to carry the hydrophone equipment humans would otherwise be using.

Future Focus

For accident investigators like Mark Ford, the next generation connected units will allow for a much faster information gathering process. “Clearly the big benefit for us is, rather than having to go out to sea or visit the accident site, in theory we will circumnavigate that part,” says Ford.

There are a number of issues which sometimes makes locating the crucial devices very difficult, notes Ford. “They can be notoriously hard to find – for example, if the recorders are embedded deep into the sand or under aircraft wreckage. All of those factors can affect the range of the beacons so it can take some time.

In MH370's case, the recorders have so far, not been found. It's hoped that the connected boxes will make data retrieval faster and cheaper. Wikimedia Commons/Laurent Errera 

“Hence, this is why we’re looking to livestream the data – it’s also expensive to recover them especially if you’re working deep sea,” Ford notes.

With the connected capability right around the corner, we will soon see these devices rolled out on new and existing aircraft around the world. The development will undoubtedly change the way investigators work and should make the success rate of recovering the all-important data, which is crucial to an investigation, higher than it already is.