Why Airplane Black Box is Key to Discover Cause of China Eastern Boeing 737 Crash

Why Airplane Black Box is Key to Discover Cause of China Eastern Boeing 737 Crash
    Add a header to begin generating the table of contents

    China Eastern Airlines flight MU5735 went missing and crashed over Wuzhou city in Guangxi province on March 21 while on a mission between Kunming in Yunnan province and Guangzhou in Guangdong Province. There are 123 passengers and nine crew members in the plane. Search and rescue work are ongoing. Because the plane crashed in a mountainous area and the terrain is complicated, it is difficult to carry out the work with large equipment, so we can only rely on human and UAV search at present. An important part of the rescue effort is in search for the plane’s black box. The reporter introduced that the rescue team was equipped with flashlights to search overnight, and the soldiers carried out piece-style search with pickaxes, shovels and other tools at the scene. The airplane black box records the cockpit voice and flight data with detailed information during the flight, especially just before the accident. Only when the aircraft black box is found and combined with the wreckage will the cause of the accident be further determined.

    What is a flight data recorder/ airplane black box?

    Every plane must installed a airplane black box for flight data recording, which is made of electrical insulation and metal. There are two recorders, one is flight data recorder and the other is an aluminum cockpit voice recorder. Insulation will wrap the components and the box will be placed in stainless steel or titanium enclosures. It uses a specific algorithm to record flight information. This allows authorities to access recorded flight data when needed. Contrary to popular belief, black boxes are mostly bright orange, not black. The flight black boxes can withstand the most extreme conditions and is one of the most special tools in the aerospace research industry, with its voice recording function. At the same time, it can withstand explosive disintegration, high-temperature combustion, immersion and other damage. The battery in the black box lasts about 30 days. During this time, it will continuously send signals to the outside world. The location of the plane crash, mainly relies on visual search, after finding the wreckage, it is necessary to use the bright and unique color of the black box and reflective logo to search.

    what is airplane black box

    How do black boxes survive plane crashes?

    A airplane black box consists of a circuit board that contains all the electronic components needed to record and store data or audio. These circuit boards are also called memory boards, which are placed in an aluminum housing. Compared with alloys containing iron, aluminum is rustproof. An oxide layer forms on the aluminum housing, protecting the internal components from corrosion When exposed to water. The aluminum box is encased in a one-inch insulating layer. Insulation can withstand a temperature that is more than 2,030 degrees Fahrenheit. The insulated black boxes are wrapped in corrosion-resistant steel or titanium. A thick shell protects the internal components from shock, fire and water.

    Most airplane black boxes are designed to meet international standards created by EUROCAE. The FAA also requires black boxes to comply with European CAE standards. It’s required that a logger needs to be able to withstand an acceleration of 3400g for 6.5 milliseconds. That’s the equivalent of a 310-mile-per-hour impact. Airplane black box standards also include requirements to withstand high and low temperatures, penetration, static compression, deep-sea pressure, and immersion in seawater or fluids.

    Besides internal components protection, it’s also easier for investigators to locate the device with black box flight recorder. The Black boxes are painted bright yellow or orange with an underwater locator beacon, which activated automatically at the time of the crash. An ultrasonic wave that is undetectable by the human ear is be emitted and easily picked up by sonar equipment. Beacons pulse continuously for about 30 days and can be picked up by equipment at a depth of 6,000 meters.

    The flight data recorder and cockpit voice recorder are installed in the rear fuselage of the aircraft. The rear of the plane is the last part of the plane to be hit in a crash, maximizing the chances of survival for these devices. There have been only a few cases where the black boxes have not been found. Airplane black box is designed to provide more protection than the potential damage from a crash. Only a severe fire or impact that exceeds the designed strength of the device can damage the internal components.

    What information does the airplane black box record?

    There are two black boxes in most of the planes, among of them is the FDR, which records flight data, and the CVR, which records audio from inside the cockpit.

    hundreds to thousands of parameters per second are captured by FDR captures. It records the aircraft’s flight path, position, altitude and speed. Data related to the performance of aircraft components, such as engines and exhaust will also be stored.

    All sounds in the cockpit, such as private conversations between pilots are recorded by the CVR. The device can also capture the voice of air traffic controllers, automated computer broadcasts, passenger announcements and discussions with crew members. Older cockpit voice recorders can store up to 30 minutes of audio. For data protection purposes, audio continues to be overwritten after reaching its maximum capacity. Some modern airplane black boxes are modular. Cockpit Voice and Data recorders (CVDR) and newer personal recorders use digital technology rather than tape. Modern CVR can store over 120 minutes of audio.

    Do airplane black box actively emit signals?

    The black box sends out an active signal, a device called an underwater locator beacon that has a trigger on its side that only triggers an underwater locator beacon (ULB) when it hits water. The signal is not an electromagnetic wave, it’s an ultrasonic wave, so you can’t hear it.


    Underwater locator beacons are divided into high and low frequencies

    The high frequency “underwater locator beacon” can transmit sinusoidal signals at 37,500 Hz. Once triggered, the underwater beacons emit the signals continuously until the black box’s battery runs out. Under normal circumstances, the power of the underwater locator beacon can operate for a month. Once an airliner crashes to the sea floor, it is best to find the black box within 30 days. Otherwise, when the battery runs out and the airplane black box no longer emits signals, finding the black box is like looking for a needle in a haystack. High-frequency underwater locator beacons emit ultrasonic waves with high intensity and are easier to detect, but the signal range is limited, generally only within a range of 4 kilometers. It also takes more power, so it usually lasts only 30 days.

    Low-frequency underwater beacons use sound waves of 8,800 Hz, which are audible to the human ear and have a lower frequency, so they use less electricity and can last up to 90 days. Low frequency beacons can be transmitted from the surface of the sea to an area up to 20 kilometers away. At the bottom of the sea, the signal can still be transmitted to the surface of the sea within 6,000 meters, taking into account the loss of the signal.

    Even so, searching the ocean for airplane black box is difficult. Compared to the vast sea, the search area of more than ten kilometers is too small! China Eastern MU5735 crashed to land, so the black box’s “underwater locator beacon” will not be activated.

    Underwater locator beacons are divided into high and low frequencies

    Then why doesn’t the black box connected to GPS?

    In theory, the airplane black box can do the same as satellite positioning. However, due to various practical factors, the black box has not been equipped with satellite positioning. The theory of satellite positioning is pretty simple. People have x, Y and Z coordinates on the ground.

    why doesn't the black box connected to GPS

    The phone can calculate one of these values by picking up the time the satellites send out, and if there are three satellites it can calculate the exact location of the person. As the speed of light is fixed and the position of the satellites is different, the time signal of the three satellites received by the mobile phone finally has an error, so the fourth satellite is needed to correct the error, so at least four satellites are needed to locate.

    least four satellites are needed to locate

    Now that the principle is so simple, why aren’t black boxes equipped with GPS?

    To know that mobile phone positioning is for the user to see, even if the airplane black box can be located, only the black box knows its own position coordinates. What we need is for the search team to know the location of the black box, so this operation is unnecessary! Common mobile phone positioning, not mobile phone to send signals to the satellite, mobile phone does not have so much power to send signals to the satellite, are passive to receive satellite signals.

    Could the black box reveal its location by actively transmitting signals to satellites?

    As a matter of fact, there is no point in doing this. First, if the airplane black box could communicate with the satellite in a two-way way, it would be so powerful that the power consumption would increase dramatically and the size of the battery would also increase, which would cause the structural stability of the black box to be damaged. In addition, rather than sending signals to satellites, it would be better to increase the power and be more efficient for transmitting signals from the ground. You know, the plane black box standards for civil aircraft are from the 1980s, which means that in the past 40 years, the black box has basically not changed much. At most, some parameters are added to record. Not much progress has been made in hardware functions, especially in positioning systems.

    In conclusion, the National Transportation Safety Board has been planning to add video recording to the black box, which would record cockpit video, but pilots have been opposed to it because of privacy concerns. In terms of information storage, the new generation of aircraft black boxes may not need to be searched anymore. It can directly send flight data to the ground base station via satellite, which will realize real-time synchronization between the black box information and the ground base station.

    Talk to an Expert