What are Aircraft Black Boxes & Their Importance?
You may have heard of the infamous ‘black box’ or the Aircraft Black Boxes, the device aviation professionals always seek to recover after a plane crash so they can know what really happened.
However, you may be shocked to find out that the black box is in fact, not black and not just a single box.
The black box is actually a very bright shade of orange called “international orange”, and is more technically known as the flight recorder.
In this post, I will address:
The function of the black box,
The origin of the term,
The components of the black box,
How the black box operates,
How data is retrieved from it,
And the latest developments with aviation recorders for safety.
What Does the Black Box Do?
The black box is an instrument that records the overall performance and condition of an aeroplane during flight. It is usually the last thing to survive from ghastly plane crashes.
This is because it is constructed to be indestructible and kept in the aircraft’s tail section (or other sections at the back of the aircraft) which is least susceptible to damage in a crash.
When there is no survivor from a plane crash and the aircraft has been so badly damaged that aviation investigators cannot put the pieces together, the black box offers useful insight into the events that may have led to the plane crash.
Additionally, the black box may be used to clarify whether the pilots’ report of what happened on a plane accident/incident is true or not.
The black box is just about the size of a shoe box but it is an extremely important instrument.
The reason for it being such a bright shade of orange is to make it very conspicuous from the site of a crash; investigators need to be able to point to it easily among all the debris from the plane.
Why Is It Called a Black Box?
The term ‘black box’ was coined during the second World War, when the use of aviation recorders had become widespread. The recorder was first referred to as the black box in a May 1945 Flight article titled “Radar for Airlines”.
The original flight recorders looked different from the current ones. They were kept in non-reflective black boxes and so were just referred to as black boxes.
By 1967, the use of flight recorders had become compulsory in leading aviation countries and by then, the name had stuck even as the appearance of the recorders changed.
The original boxes were painted black in order to prevent rust of the metal components. Some people believe that the black box is actually so called because of its soot-covered appearance when it is recovered from a crash that involved fire outbreaks.
NB: there is another “black box” term used in science and engineering. It refers to a system whose inner workings are not known and is only regarded in terms of its inputs and outputs when analysis is carried out.
Parts of the Black Box
The black box consists of two main units namely, the flight data recorder (FDR) and the cockpit voice recorder (CVR). In modern black boxes, the two units are often combined into a single device.
- Flight data recorder: the FDR records variables such as airspeed, vertical acceleration, altitude, heading, pitch, fuel flow and the conditions of the internal environment of the plane. It also records the instructions sent to any electronic systems (instruments) on the plane. It has 17-25 hours of recording storage, enough for multiple long haul flights.
- Cockpit voice recorder: the CVR records verbal interactions between both pilots in the cockpit, and between the pilots and the ATC on the ground. It also records the sounds of switches, the engine and other background noise that can be heard from the cockpit. These can help ascertain whether the some parts of the aircraft were running properly in the final hours of flights. The CVR only has recording storage of 2 hours, meaning it only captures the last 2 hours of flight. In the event of a crash, the information recorded by the CVR is transcribed into documents that are sent to investigators, along with the recordings themselves.
The black box also has other parts such as:
- The underwater locator beacon in front of the devices.
- Solid-state memory boards which store information. The early flight recorders used magnetic tape instead, but by the 90’s, the advent of solid-state technology made for more durable and easier-to-retrieve devices.
- The crash-survivable memorable unit in which the memory boards are kept.
- Power supply.
- High-temperature insulation.
- Stainless steel or titanium housing. There is also a thin layer of aluminium housing around the memory boards.
How the Black Box Operates
The voice and data recordings of the black box are stored in digital formats on solid-state memory boards. The recordings are made in continuous loops, meaning old data is constantly replaced by new data.
This is how the CVR is only able to record information from the final hours of flight. The old recorders which used magnetic tape only had a recording storage of 30 minutes.
The memory unit is designed to survive extremely severe conditions. Before the black box is okayed for use, it is tested to see if it can withstand the following:
- Impact with a concrete wall at a speed of 750 km/h,
- Shooting the unit down an air canon to create an impact magnitude of 3,400 g (units of gravitational acceleration),
- A static load of 2.5 tonnes for at least 5 minutes,
- A maximum flame temperature of 1,100 °C for at least one hour,
- The water pressure that is found at 6,000 m/ 20,000 ft in salt water for at least 24 hours,
- Submersion in saltwater for at least 30 days,
- Immersion in aviation fluids such as jet fuel, lubricants, hydraulic fluids, etc.
The data collected by the aircraft’s sensors are sent to the flight data acquisition unit (FDAU) in the avionics bay, which is at the front of the aircraft. The FDAU then sends these data to the FDR at the back of the aircraft. Generally, each parameter is recorded multiple times in a second. Every pilot command is recorded by the FDR.
The CVR is connected to all the microphones that may be found in the cockpit. An associated control unit pre-amplifies the audio signals from the microphones before sending it to the CVR. The CVR then digitises the audio signals.
The microphones in commercial aircraft are typically up to four: one in each pilot’s headset, one in the third crew member’s headset (if there is one), and one near the center of the cockpit or in the cockpit roof to pick up other sounds.
The memory boards store the data that is recorded by the CVR and FDR. It is made of stacked memory chips. It has no moving parts which makes it easier to maintain and less susceptible to damage.
The solid-state recorders can record thousands of parameters – however, only 88 are mandated by the Federal Aviation Administration (FAA). This translates to several terabytes of data stored per flight thus, complex data management systems are required to analyse these data.
Many modern aircraft are equipped with an “event” button. In the event of an abnormality, the button can be pressed so that a signal can be placed on the recording which marks the time of the event.
The black box is connected to either of the aircraft’s generators for power supply, however, they also have their own batteries in case the aircraft electrical system fails.
If the plane crashes in the sea, the underwater locator beacon emits an ultrasonic pulse in the form of a ping sound.
This sound can be detected by sonar and audio equipment and is emitted once per second for at least 30 days – the duration of which the beacon’s battery is expected to last for.
The beacon only emits this sound when the black box is under water to aid its recovery. Thus, if no sound is detected, it is clear to investigators to look for the box on land.
How Information Is Retrieved from the Black Box
After the black box is recovered, aviation investigators take the CVR and FDR to a lab where they can download the data and attempt to fully recapture how the accident occurred.
The process requires a lot of patience and meticulousness, often taking week or months to be completed.
In the US, the manufacturers of the black box provide the National Transportation Safety Board (NTSB) with the readout and data management systems required for analysis.
If the FDR is not damaged, investigators can simply connect it to a readout system, so they can extract the stored data. This can be done using USB or Ethernet ports.
However, if the FDR is damaged as is likely the case, the memory boards are removed, cleaned up and fitted with a new memory interface cable. This then allows the memory board to be connected to a working recorder, so the data can be extracted.
The team of experts who analyse the data include representatives from the airline and plane manufacturer, an NTSB transportation-safety specialist and an NTSB air-safety investigator.
The Future of the Black Box
In recent years, it has been looking more and more like the black box will be replaced – in commercial aircraft – in favour ofsystems that can give complete status reports in real time.
This development was especially triggered by the disappearance of the Malaysia Airlines Flight 370.
Critics suggest that if such a system had been on the aircraft, investigators would have concluded the search and rescue within a matter of hours since it would be traced to the last transmitted location which would have been made seconds before its crash.
To this day, no one knows the whereabouts of the plane, or has even been able to recover the black box.
One of such suggested systems is ADS-B which stands for Automatic Dependent Surveillance Broadcast. ADS-B enables aircraft to automatically transmit and/or receive relevant data in the form of a broadcast data link to nearby ground stations.
It does not record data of its own, but rather relies on other aircraft systems to record data and then send the data to it. ADS-B is space-based, meaning it communicates with satellites which are outside the earth’s atmosphere.
The broadcast data link sent by ADS-B can be sent to ground stations for surveillance (ADS-B Out) or to surrounding aircraft to increase their situational awareness (ADS-B In). ADS-B requires that there are several broadcast stations/towers along the course of the aircraft.
The broadcast nature of ADS-B means it does not involve any two-way communication. ADS-B works alongside Surface Movement Radars (SMRs) in terminal areas.
The SMRs demodulate the received signal and tags the aircraft with its call sign and Mode S address, data which can be used to obtain the call sign and flight number.
‘ADS-B Out’ mode uses the transponders on board and works hand in hand with the Flight Management System or GPS directly. ‘ADS-B In’ requires that there is a receiver, computer and any suitable cockpit display.ADS-B has a coverage of about 130 nautical miles (NM)
ADS-B is a relatively new system and so, has not been installed in a lot of aircraft. Only about 700 aircraft are reportedly ADS-B equipped.
However, as of early 2020, FAA mandated ADS-B compliance in the B777 200 series for aircraft with engine-driven electrical systems in certain airspace categories.
United Parcel Service (UPS) aircraft in the US have equipped some of their fleet with modern ADS-B technology since 2016. Some reports have been made concerning poor GPS reception in some terminal areas with large structures.
This poor GPS reception is a major hindrance to ADS-B Out transponders which have even led to their failure in the past. This called for the incorporation of more modern and accurate Generation 3 GPS receivers in their aircraft which initially was not readily available but now is.
One shortcoming of ADS-B is that is not able to record and store nearly as much data as the black box, but efforts to make this possible are underway.
Advanced ADS-B systems would only be a replacement for the FDR since they cannot record voice data. Thus, even with this development, CVRs would still be a necessary part of aircraft.
Some aviation bodies have tried to implement devices that can capture visuals too into the black boxes, but pilots have protested against this, saying it would violate their privacy and that the current black boxes already capture all the necessary information.
Airbus helicopters currently have a Vision 1000 system that records from behind the pilot’s head. The camera is able to pick up the pilot’s actions, the cockpit area, and the view beyond the windshield at four frames/second.
References
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Bonsor, K. and Chandler, N., 2022. How Black Boxes Work. [online] HowStuffWorks. Available at: <https://science.howstuffworks.com/transport/flight/modern/black-box.htm> [Accessed 18 May 2022].
The Times of India. 2020. Airplane black box: All you need to know about the device | India News – Times of India. [online] Available at: <https://timesofindia.indiatimes.com/india/airplane-black-box-all-you-need-to-know-about-the-device/articleshow/77434032.cms> [Accessed 18 May 2022].
En.wikipedia.org. n.d. Flight recorder – Wikipedia. [online] Available at: <https://en.wikipedia.org/wiki/Flight_recorder#:~:text=The%20term%20%22black%20box%22%20was,reflective%20black%20boxes%20or%20housings.> [Accessed 18 May 2022].
Finlay, M., 2020. What Are Black Boxes On An Aircraft And Why Are They Important?. [online] Simple Flying. Available at: <https://simpleflying.com/black-boxes/> [Accessed 18 May 2022].
