Eight things you might not know about black boxes

With the crashes of AirAsia flight QZ8501 and Malaysia Airlines MH17, along with the disappearance of flight MH370, there is again focus on airline "black boxes".

What is "black box"?

An airplane actually has two black boxes: a flight data recorder, which stores information on specific parameters such as flight control and engine performance, and a cockpit voice recorder, which records background sound and conversations between crew members and air traffic control.


Here are some things you might not know about black boxes.

1. They're not black:  Black boxes are the same colour as the Golden Gate Bridge in San Francisco ... kind of. They are a tone of what's known as international orange, which is a set of three colours used in aerospace and engineering to distinguish objects from their surroundings. The Golden Gate Bridge is a darker shade, while the international orange used for black boxes is much brighter.
   
2. A 'black box' comes in two parts:  The "black box" is made up of two separate pieces of equipment: the flight data recorder (FDR) and a cockpit voice recorder (CVR). They are compulsory on any commercial flight or corporate jet, and are usually kept in the tail of an aircraft, where they are more likely to survive a crash. FDRs record things like airspeed, altitude, vertical acceleration and fuel flow. Early versions used wire string to encode the data; these days they use solid-state memory boards. Solid-state recorders in large aircraft can track more than 700 parameters.
   
3. They were invented by an Australian:  Dr David Warren's own father was killed in a Bass Strait plane crash in 1934, when David was just nine years old. In the early 1950s, Dr Warren had an idea for a unit that could record flight data and cockpit conversations, to help analysts piece together the events that led to an accident. He wrote a memo for the Aeronautical Research Centre in Melbourne called "A Device for Assisting Investigation into Aircraft Accidents", and in 1956 produced a prototype flight recorder called the "ARL Flight Memory Unit". His invention did not get much attention until five years later, and the units were eventually manufactured in the UK and US. However, Australia was the first country to make the technology compulsory.
   
4. Experts don't call them "black boxes":  The term "black box" is favoured by the media, but most people in the know don't call them that. There are several theories for the original of the name "black box", ranging from early designs being perfectly dark inside, to a journalist's description of a "wonderful black box", to charring that happens in post-accident fires.
   
5. Only 2 hours of cockpit conversations are kept:  Digital recorders have enough storage for 25 hours of flight data but only two hours of cockpit voice recording, which is recorded over itself in a loop. The CVRs track the crew's interactions with each other and air traffic control, but also background noise that can give vital clues to investigators. Earlier magnetic tape versions could only record 30 minutes of cockpit conversations and noise, which was also recorded in a loop.
   
6. It can take a long time to find one:  Black boxes are fitted with an underwater locator beacon that starts emitting a pulse if its sensor touches water. They work to a depth of just over four kilometres, and can "ping" once a second for 30 days before the battery runs out, meaning MH370's black box stopped pinging around April 7, 2014. After Air France flight 447 crashed into the Atlantic Ocean, it took search teams two years to find and raise the black boxes. They provided valuable information about what actually happened prior to the crash.
   
7. They're virtually indestructible:  FDRs are usually double-wrapped in titanium or stainless steel, and must be able to withstand atrocious conditions. The crucial part that contains the memory boards, the CSMU, is shot out of an air cannon to create an impact of 3,400 Gs and then smashed against a target. It is subjected to a 227kg weight with a pin attached to it, which is dropped onto the unit from a height of three metres. Researchers try to crush it, destroy it in an hour of 1,100 degree Celsius fire, submerge it in a pressurised salt water tank, and immerse it in jet fuel.
   
8. But they're not as powerful as your phone:  In the aftermath of MH370, experts say it might be time to update methods of collecting flight data. Passengers are able to text, stream and surf the internet but the data recorders on board are not communicating in real time with the rest of the world. However, the bandwidth needed to stream huge amounts of data from large aircraft is not currently feasible. Aviation author Stephen Trimble writes in the Guardian that Boeing has applied for a patent on a system that will transmit a subset of data including the plane's location. 

Taken from:  abc.net.au