Multi-Axial Accelerometer

From the time that Wilbur and Orville Wright made their first powered flight in 1903, there has been a need to record flight data. In the case of the Wrights, they wanted to know how many turns the propellers had made during a flight, which was information that was useful in determining – and improving – the propulsive efficiency with the propellers.

For the most part, the next 40 years of flight data was primarily of interest to those engaged in building and testing new aircraft designs and that information was recorded by hand during the test flights, or in post-flight pilot observations. In 1939, however, two French inventors developed a device that automatically recorded several flight parameters on slowly moving photographic film that was exposed to a thin beam of light bent by moving mirrors. Because the container needed to be completely lightproof,some believe that this may have been the origin of the phrase “black box” as being synonymous with flight data recorder.

While recorded flight data continued to be important in understanding how new aircraft designs were performing purely from an engineering standpoint, with increasing numbers of people flying aboard commercial airliners by the 1950s – the challenge of understanding aviation accidents of production airplanes became the driving interest in understanding what – and why – things sometimes went wrong during flight. Realizing that accident investigators very rarely had the luxury of the first-hand observations of the cockpit crews involved in accidents, in 1953 an Australian aviation engineer, David Warren, built the first flight data recorder that also recorded the conversation of the cockpit crew. Warren realized that the comments of the flight crew, recorded concurrently with certain physical data about the airplane itself, could prove invaluable in determining why an accident happened.

By 1960, the Australian government mandated that all commercial airliners be equipped with cockpit voice recorders (CVRs) and flight data recorders, and soon the United States and most industrialized nations around the world followed suit.

In the half-century since data and voice recorders have been required, equipment on all scheduled airlines flights, the devices have evolved to measure not just the early 1960s parameters of airspeed, altitude, heading and attitude (whether the nose of the airplane is pointed up or down, or the wings are level or banked), but thousands of other parameters which can help pinpoint why an accident happened. Beyond the post-accident investigatory importance of this information, the recorded data from normal, day-to-day flights is proving increasingly useful to aircraft owners and operators who periodically download it for computer analysis which can reveal maintenance concerns in their earliest stages of development, or can help determine more cost-effective ways in which the aircraft can be operated.

Flight Data Recorder (FDR) is a device which records multiple parameters of aircraft performance for the purpose of helping safety investigators determine the cause of an accident. Additionally, the recorded data can be used in normal (non-accident) operations to detect maintenance issues which may be developing, or to improve efficiency by better understanding how normal flight operations are being conducted.

Although the use of flight data gathered during day-to-day normal flight operations is becoming increasingly important for owners and operators of aircraft, the FDR’s historically famous role remains being one of the so-called “black boxes” which are recovered following an accident (the other black box being the cockpit voice recorder (CVR)). This is because in the past half-century in which the use of FDRs and CVRs have been mandated by aviation regulatory authorities around the world, the knowledge gained from these devices have led to major improvements in air safety, not only in the mechanical aspects of aircraft themselves, but in how flight crews conduct flight operations.

An FDR performs three functions:

• Collects data, Flight Data Acquisition Unit (FDAU)

• Records that data, Solid-State Memory (SSM)

• Protects that data from loss in the event of an accident, Crash-Survivable Memory Unit (CSMU)

Whether an aircraft is taxiing, taking off, landing or in an extended period of cruising flight, it is generating vast amounts of data. In modern aircraft, almost all of this digital data is already being generated for the aircraft systems, which require it.

For example, temperature and altitude (atmospheric pressure) data is needed by the engine control system, while airspeed, heading and position data is needed by the navigation system. In these cases all the Flight Data Acquisition Unit (FDAU) needs to do is tap into the digital data stream of the respective systems. Other types of data are only critical in the investigation of an accident, and for this purpose dedicated sensors are installed which provide this information to the FDAU. An example of this kind of data would be the output of an accelerometer, which measures the acceleration (G-forces) the aircraft is experiencing at any given moment.

It is fair to say that the one aspect of an FDR that distinguishes it from any other technological product ever made is its ability to survive an accident and still allow recovery of the stored data. This is accomplished by the Crash-Survivable Memory Unit (CSMU), which is collectively the solid-state memory chips and a hardened metal container filled with specially designed heat insulating material. It is this container that provides the survivability, for it is able to withstand massive crushing loads, intense heat, and exceptionally high G-forces, all of which is proven by crash survivability testing.

Elements of crash survivability include:

• Resistance to impact and G-forces: The CSMU must not only withstand an impact at very high speed, but sudden deceleration which produces extreme G-forces

• Resistance to crushing loads: The CSMU must be able to withstand the weight of tons of debris under which it may be resting following an accident

• Resistance to intense heat and “heat soaking”: The CSMU must not only be able to withstand the intense heat of a raging fire, but the often more damaging effects of “heat soaking,” which means a lower level of heat to which the unit is subjected to for hours, such as residual fire that may burn for an extended period following an accident

• Resistance to submersion at great depths: The CSMU must be able to withstand the tremendous pressure of being submerged thousands of feet below the ocean’s surface

Automatic Identification System (AIS) is a VHF-based transponder system for:

Collision avoidance - Enable vessels to identify radar contacts with vessel identification and communication details

Maritime surveillance - Maritime authorities can identify all AIS-equipped vessels operating within VHF range of their shore stations and air-sea platforms

Asset management - Secure AIS allows maritime authorities to track their air-sea assets securely through the use of encrypted AIS messages

Anomaly detection - AIS provides a means for automating detection of maritime anomalies such as vessel intrusion, unidentified radar/sonar contacts, and suspicious maritime activity

“Black Box” is the name widely used for a flight data recorder or cockpit voice recorder. They are, however, not black, but are painted a high-visibility orange to help safety investigators locate them following an accident. So how did something that is universally orange become called “black”?

There is no definitive answer, but it is possible that aviation black boxes may have originally picked up the moniker because some of the earliest flight data recorders which were developed in the early 1940s employed photographic film as the recording medium; therefore, the inside of the box had to be completely dark as a narrow beam of light “wrote” data on a strip of film.

More likely, though, the term “black box” became associated with aviation FDRs and CVRs because, broadly speaking, a black box is any electronic device which has an input and an output over which the operator of the device has no control, that is, what goes on inside the device happens “in the dark” from the viewpoint of the operator. This is essentially the case with FDRs and CVRs – the devices automatically do their job with no involvement from the flight crew.

Although among the general population the term is almost exclusively associated with the FDRs and CVRs carried aboard aircraft, in recent years “black box” is tied to a similar type of accident investigation technology being used on passenger ships and freighters. In this maritime application the device is known as a hardened voyage recorder (HVR). And, it too is painted orange.

Similar to the flash memory found in a myriad of consumer electronics, the digital data that has been collected by the FDAU is stored on memory chips. These chips are specifically made for FDRs, and are therefore more resistant to heat and G-forces than those found in consumer goods.

An FDR always retains the last 25 hours of flight data by continuously recording over data which is more than 25 (operational) hours old. Because of this capacity, there is no non-stop or multi-stop flight which can’t be recorded in its entirety. An FDR’s memory can be configured to store more than 25 hours by employing data compression and other techniques.