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Recovering data from black boxes

While air travel is consistently rated as one of safest forms of transport, recent disasters including ill-fated flight Air Asia QZ8501 from Surabaya to Singapore,  MH370 from Kuala Lumpur to Beijing, which disappeared without a trace in the middle of the Indian Ocean and flight MH17 from Amsterdam to Kuala Lumpur, which was struck down by a missile fired by pro-Russian separatists fighting against the Ukrainian government, remind us that there will always be a need for black box technology and recovery.

Orange is the true black

But while many of us have heard of the black box and appreciate their importance, how much do we really know about this crucial piece of equipment?  For a start, many of us are unaware of the fact that each black box has two elements or that they are not actually black at all but orange in colour to make them easier to spot in wreckage.

The first element of ‘orange’ black boxes contains the Cockpit Voice Recorder, a microphone that records any conversations between crew members as well as background noise that could help to provide significant clues about a crash.  The black box records sound in analogue, then converts it into a digital format, which means that only the last two hours of sound from the cockpit can be analysed as the system continuously rewrites over the digitised data.

The second element is the Flight Data Acquisition Unit (FDAU), which records the vital operating functions of the aircraft.  FDAUs store a minimum of 25 hours of flight data and gathers data from sensors to piece together how, when and why a plane didn’t make it to its designated destination.  Sensors can pick up on everything from altitude and travelling speed, to the direction in which a plane was travelling and the speed of its rotors.

Following the pinger

Investigators use information from the black box to understand as much as possible about a plane’s activity before a crash.  As soon as power is lost on a plane the black box is disconnected and a second internal power supply is initiated that starts the box’s ‘pinger’ working.  The pinger emits a periodic signal and this can be picked up by investigators searching for lost aircraft.

Built to last

Given the importance of black boxes, they’ve undergone rigorous tests to ensure they are built to last. Black boxes are double-wrapped in titanium or stainless steel and designed to withstand the harshest conditions. Researchers have shot them out of air cannons and tested their endurance when exposed to 1,100 degree Celsius heat and -55 degree freezing conditions.

They also comply with the standard CAE ED-112, which means they can cope with the impact of physical shock measuring up to 3,400 gs (normal gravitational force is just 1g).  Crash survivable memory units (CSMUs) are often the only element of a black box to survive intact.

First generation black boxes used basic magnetic strips to store data and these were superseded first by magnetic tape and then by solid state drives (SSDs), which are used in the current generation of boxes.

One size does not fit all

There are only a handful of manufacturers across the world and they design specific versions of their black boxes for different types of aircraft: an Airbus will have different housing and connectivity for its black box than a private jet, for example.  A further complication for those recovering data from black boxes is that each manufacturer has its own proprietary technology for storing and encrypting data.

The challenges of SSDs

Another challenge is that it can be difficult to recover data from SSDs in general. There are many benefits to SSDs, which are the same drives that are used in modern laptops, often supplementing traditional hard disk drives (HDDs).  Compared to hard drives, they are much quicker, quieter and smaller and run off semiconductor memory- which means there are no moving parts making them less prone to physical damage.

However, these same benefits make recovering data from SSDs tricky as well.  The small size, speed and the lack of moving parts enables SSDs to be integrated within smaller devices. They are usually wired into the circuit boards of devices alongside all other electronic components. This means that fault isolation and repair are far more complex than from a removable drive and require experienced professionals to extract data –especially in an event of a plane crash when so much damage can take place and the information in the black boxes hold vital clues to investigators.

Recovering vital data

Despite all the efforts to make black boxes indestructible, they can still get damaged, and when that happens there’s a need to get professional support to extract data from the SSDs.  When a black box is recovered it is typically taken to a specialist engineering lab, where printed circuit boards (PCBs) and chipsets are carefully removed and plugged into a special rig in which they can be analysed using specialist software from the black box manufacturer.

Engineers work to analyse data extracted from the black box, often repairing any memory cards that have been damaged and tracing data that may be replicated from one chip to another and can therefore be recovered.  Every case is different – according to the black box manufacturer, the amount of physical damage and the level of data encryption employed by the SSD.

Only engineers with the right level of technical expertise and ability to build a comprehensive picture from a number of different data sources – with an understanding that their conclusions will have enormous repercussions for different parties involved in an aviation incident – can manage such delicate and complex work. Findings will be used by both the prosecution and the defence in cases or investigations so should be held securely and prove beyond doubt that data is accurate.

Improving black box technology

With all of this in mind, manufacturers continue to work to improve the technology that underpins black boxes and there are some suggested ways forward. One of these is to enable planes to stream live data periodically via satellite so that investigators can look at this data rather than rely on black boxes.  However, with 1300 flights a day in the UK and 2400 in the US alone this would be an enormous undertaking using today’s infrastructure and would require considerable investment.

Another improvement under consideration is to ensure that each black box’s pinger could transmit a unique signal for its parent aircraft.  This would help to speed up recovery overall as there would be less false signals followed by teams trying to locate lost planes.

However, as black box technology develops in the future, there is always going to be a need for specialist skills to pick up the pieces after an airborne disaster to get to the truth of what happened.

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