Nepal plane crash: What colour is a black box, how does it work? Explained

Nepal plane crash: A police man carries the black box after it was recovered from a Sita airplane wreckage after it crashed.

The black box of the crashed Yeti Airlines' aircraft in Nepal with 72 people, including five Indians, on board was recovered on Monday, as rescue workers retrieved 69 bodies from the accident site in the resort city of Pokhara. Both the cockpit voice recorder and flight data recorder have been recovered as search and rescue teams rappelled down a 300-metre gorge to continue their efforts, which were suspended overnight, officials said.

The boxes could offer vital clues about Sunday's crash - Nepal's deadliest aviation accident in over 30 years.

Here is how a black box helps investigators find out more about a plane accident:

The “black box” is usually two different boxes with different functions. The name itself is a misnomer because neither of these are black nor resemble a box.

What is it made of?
The black box is made of two separate pieces of equipment: Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR).

What does FDR do?

The flight data recorder (FDR) records more than 80 different types of information such as speed, altitude and direction, as well as pilot actions and performance of important systems. The FDR records aircraft system and flight data, such as the position of control surfaces (flaps, elevator, rudder, ailerons), barometric data (altitude, airspeed, vertical speed, engine performance, etc)

What does CVR do?

The Cockpit Voice Recorder (CVR) records radio transmissions and other sounds in the cockpit, such as conversations between the pilots, and engine noises. The CVR is a multi-track audio recorder that continuously captures every audible sound in the cockpit.

What colour is a black box?

Black boxes are not black. They are bright yellow or orange. The bright colour is used to assist in locating the boxes after an accident. Before airlines made day-glow orange a standard colour for the flight recorders, some Boeings used a yellow sphere.

Why is it called so?

There are several theories about the origin of the name “black box”. The most widely accepted one refers to the early black box designs which were dark inside. Another view is that it got its name from its charred look due to post-accident fires.

What does it look like?

Black boxes don’t look like boxes. The device may come in a variety of shapes, including spheres, cylinders and domes. It has to be large enough for investigators to find among the plane’s debris.
How is it traced after plane accidents?

Black boxes have an underwater locator beacon that starts emitting a pulse if its sensor touches water. They can only be detected if the aircraft is under water. If a crash happens on land, investigators have to depend on its orange colour that acts as a beacon.