Why do we need to find the black box in a plane crash? How important is it?

Experts in this article:

Liu Yuxuan, Tianjin Foreign Studies University

Qizheng Yi, Composite Materials and Engineering, Shenyang Aerospace University

This article was reviewed by Lin Wenjie, engineer, senior researcher at Chuanduo Think Tank

On March 21, China Eastern Airlines flight MU5735 lost contact and crashed over Wuzhou, Guangxi, while performing a mission from Kunming, Yunnan to Guangzhou, Guangdong. There were 123 passengers and 9 crew members on board. Currently, all relevant functional departments are still carrying out intensive search and rescue work.

As an important flight data recorder, the black box records a lot of important information during the flight and becomes the key to solving the cause of the flight accident.

According to the latest information revealed by the State Council Investigation Team at a press conference on the evening of March 22, no survivors have been found on board so far during the rescue process. The press conference also mentioned that the two black boxes on board will be searched as soon as possible.

On March 22, staff searched for the black box at the crash site of China Eastern Airlines MU5735. Photo by Xinhua News Agency reporter Zhou Hua

So, what exactly is a black box? Why is it so important to aviation accident investigations? Let’s take a look…

Is the black box black?

Black box is the common name for aviation flight recorders, which are now generally orange in color.

During World War II, aviation flight recorders began to be installed on military aircraft. After the war, this technology was applied to civilian aircraft, which was the prototype of the black box. By 1954, this instrument was uniformly installed in a black box, which is the origin of the name black box.

However, in order to facilitate searching after an accident, the black boxes are now painted a striking orange color, and some even have reflective strips.

Modern black box Source: Xinhuanet

How important are black boxes to aviation accident investigations?

The official name of the black box is "flight information recorder". A complete black box system is mainly composed of a cockpit voice recorder (CVR) and a flight data recorder (FDR). In other words, an aircraft has two black boxes with different functions.

On March 22, staff searched for the black box at the crash site of China Eastern Airlines MU5735. Photo by Xinhua News Agency reporter Zhou Hua

The cockpit call recorder can record various conversations taking place on an aircraft. It has multiple sets of audio tracks, which can respectively record conversations between the pilot and the ground control tower, conversations between pilots, broadcasts from the captain and flight attendants to passengers, various abnormal sounds and various sounds in the cockpit, which can help investigators analyze the cause of the accident.

The flight data recorder can record all kinds of flight data, including flight attitude, flight trajectory, etc. There are various sensors all over the plane, which send data to the flight data recorder, which then records it. The flight data recorder is like a recorder that records everything, providing important data support for the analysis of air crashes.

Will the black box be damaged?

The black box is not big, weighing only a few kilograms and only one-third the size of an ordinary drawer.

Modern black boxes are resistant to high temperatures and high pressures. They can withstand a maximum overload of 3400G for 11 milliseconds, and can withstand temperatures of 1100°C for up to one hour. They can also be immersed in seawater for several months while still ensuring the integrity of the internal data.

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The black box is usually placed in the safest part of the tail of the aircraft and is also placed in a special safety container, so it can be said to be foolproof.

After entering the 21st century, the storage medium of the black box has also changed from magnetic tape to today's more reliable solid-state storage chip, which can store up to two hours of audio and 25 hours of flight data.

How do search and rescue personnel generally search for black boxes?

The black box is mainly located underwater by underwater positioning beacons. The black box will emit a pulse signal at a fixed frequency. The built-in battery of the black box can keep it working continuously for 30 days. The search and rescue personnel will use sonar detectors to detect its location and then salvage it.

On March 22, staff searched for the black box at the crash site of China Eastern Airlines MU5735. Photo by Xinhua News Agency reporter Zhou Hua

The black box that crashed on land mainly relies on manual visual search. After finding the crash site, the black box's bright and unique color and reflective markings are used for search. Search and rescue personnel can also rely on more search equipment (such as multi-rotor drones) to search.

However, the crash site of this air crash has complex terrain and dense vegetation, so it can be said that the search and rescue mission is more difficult than usual.

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