What is a Black Box? The device that can solve mystery behind Gen Bipin Rawat's helicopter crash

A Black Box is a vital electronic device also known as Flight Data Recorder that records 88 vital parameters about a flight including, airspeed, altitude, cockpit conversations, and air pressure among others.

Image for representation

The sudden and untimely passing away of the Chief of Defence Staff (CDS) General Bipin Rawat in a military helicopter crash near Coonoor in Tamil Nadu has raised the big question about how the crash happened. Officers from the Indian Air Force are at the crash site collecting all relevant data and material to ascertain the cause of the crash that led to death of multiple armed forces officers including Gen Rawat.

The emphasis of the technical team from the IAF would be to find the Black Box (if it hasn't been retrieved till now), a vital electronic device, also known as Flight Data Recorder that records 88 vital parameters about a flight including, airspeed, altitude, cockpit conversations, and air pressure among others. When a crash happens, the black box is located on a priority basis to understand what actually caused the crash. Here is how the process works.

What is a Black Box?

A Black Box is neither black in colour, nor box in shape, but is actually a compressor shaped device made in high-visibility orange colour. Experts disagree how the nickname originated, but many historians attribute their invention to Australian scientist David Warren in the 1950s. A Black Box is mandatory for all commercial airliner and armed forces to preserve clues from cockpit sounds and data to help prevent future accidents.

What's inside a Black Box?

A typical Black Box weighs about 10 pounds (4.5 kilos) and contain four main parts:

- A chassis or interface designed to fix the device and facilitate recording and playback

- An underwater locator beacon

- The core housing or 'Crash Survivable Memory Unit' made of stainless steel or titanium

- Inside there, the precious finger-nail sized recording chips on circuit boards 

There are two recorders: a Cockpit Voice Recorder (CVR) for pilot voices or cockpit sounds and a Flight Data Recorder (FDR). The BEA released a photo of the FDR from the Ethiopian jet appearing to show that the chip's crucial housing is intact while the replaceable chassis is crushed.

How is recording sourced? 

Technicians peel away protective material and carefully clean connections to make sure they do not accidentally erase data. The audio or data file must be downloaded and copied. The data itself means nothing at first. It must be decoded from raw files before being turned into graphs. Investigators sometimes use "spectral analysis" - a way of examining sounds that allows the scientists to pick out barely audible alarms or the first fleeting crack of an explosion.

How is data processed?

There's a listening room like a recording studio with audio mixing and playback equipment linked to a screen showing synchronized data. Four channels separate voices and ambient noise. Only the main investigator and a handful of people hear most tapes, which are then sealed. A technician will first prepare the recording to ensure it is intact. In France, Trauma counselling is available for staff hearing tapes.

When will the result come?

Investigators prefer to work methodically, but public and media pressure can be intense. Depending on any damage to the boxes and type of accident, some investigators acknowledge they can get a very basic idea in days or even hours. But they stress this is not always the case and rarely the whole story. Interim reports are published over a month after the black box is retrieved, but are often sparse. Deeper investigations take a year or more to complete. A Lebanese investigation into an Ethiopian Airlines crash in 2010, took two years.

Modern day Black Box

While the older models used to record on wire, foil or reels of magnetic tape, modern versions use computer chips housed inside "crash-survivable" containers able to withstand g-forces 3,400 times the feeling of gravity. Since the crash and the unresolved disappearance in 2014 of Malaysian Airlines MH370, there has been intense debate about whether black boxes should stream live data back to the ground, which involves high cost and manpower. 

With inputs from Reuters