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The “Black Box” – Brief History and Future Developments

Whenever there’s an aircraft accident, the term “black box” typically gets mentioned in the news. That’s because of the crucial role it plays in finding out what happened. But before we go any further, we must clear up one misconception, the black box is in fact painted bright orange so its easily located amongst the wreckage after a tragic crash.

For more than 60 years, investigators have used black boxes to determine what caused an aircraft accident. They use information from the Flight Data Recorder(FDR) and Cockpit Voice Recorder (CVR) to reach their conclusions. The two flight recorders are required by international regulation, overseen by the International Civil Aviation Organisation, to be capable of surviving the conditions likely to be encountered in a severe aircraft accident. For this reason, they are typically specified to withstand an impact of 3400 g and temperatures of over 1,000 °C, as required by EUROCAE ED-112. They have been a mandatory requirement in commercial aircraft since 1967.

But where did it all start?

One of the earliest and proven attempts was made by François Hussenot and Paul Beaudouin in 1939 at the Marignane flight test centre, France, with their "type HB" flight recorder; they were essentially photograph-based flight recorders, because the record was made on a scrolling photographic film 8 metres long by 88 millimetres wide. The latent image was made by a thin ray of light deviated by a mirror tilted according to the magnitude of the data to be recorded (altitude, speed, etc.). A pre-production run of 25 "HB" recorders was ordered in 1941 and HB recorders remained in use in French flight test centres well into the 1970s.

François Hussenot

In 1947, Hussenot founded the Société Française des Instruments de Mesure with Beaudouin and another associate, so as to market his invention, which was also known as the "hussenograph". This company went on to become a major supplier of data recorders, used not only aboard aircraft but also trains and other vehicles. SFIM is today part of the Safran group and is still present in the flight recorder market. The advantage of the film technology was that it could be easily developed afterwards and provides a durable, visual feedback of the flight parameters without needing any playback device. On the other hand, unlike magnetic tapes or later flash memory-based technology, a photographic film cannot be erased and reused, and so must be changed periodically. The technology was reserved for one-shot uses, mostly during planned test flights: it was not mounted aboard civilian aircraft during routine commercial flights. Also, cockpit conversation was not recorded.


Another form of flight data recorder was developed in the UK during World War II. Len Harrison and Vic Husband developed a unit that could withstand a crash and fire to keep the flight data intact. The unit was the forerunner of today's recorders, in being able to withstand conditions that aircrew could not. It used copper foil as the recording medium, with various styli, corresponding to various instruments or aircraft controls, indenting the foil. The foil was periodically advanced at set time intervals, giving a history of the aircraft’s instrument readings and control settings. The unit was developed at Farnborough for the Ministry of Aircraft Production. At the war's end the Ministry got Harrison and Husband to sign over their invention to it and the Ministry patented it under British patent 19330/45.

The first modern flight data recorder, called "Mata Hari", was created in 1942 by Finnish aviation engineer Veijo Hietala. This black high-tech mechanical box was able to record all important details during test flights of fighter aircraft that the Finnish army repaired or built in its main aviation factory in Tampere, Finland.

During World War II both British and American air forces successfully experimented with aircraft voice recorders. In August 1943 the USAAF conducted an experiment with a magnetic wire recorder to capture the inter-phone conversations of a B-17 bomber flight crew on a combat mission over Nazi-occupied France. The recording was broadcast back to the United States by radio two days afterwards.

Magnetic Wire Recorder

In 1953, while working at the Aeronautical Research Laboratories (ARL) of the Defence Science and Technology Organisation, in Melbourne, Australian research scientist David Warren conceived a device that would record not only the instrument readings, but also the voices in the cockpit. In 1954 he published a report entitled "A Device for Assisting Investigation into Aircraft Accidents".

David Warren ARL Flight Memory Unit

Warren built a prototype FDR called "The ARL Flight Memory Unit" in 1956, and in 1958 he built the first combined FDR/CVR prototype. It was designed with civilian aircraft in mind, explicitly for post-crash examination purposes. Aviation authorities from around the world were largely uninterested at first, but this changed in 1958 when Sir Robert Hardingham, the Secretary of the British Air Registration Board, visited the ARL and was introduced to David Warren. Hardingham realised the significance of the invention and arranged for Warren to demonstrate the prototype in the UK.

The ARL assigned an engineering team to help Warren develop the prototype to airborne stage. The team, consisting of electronics engineers Lane Sear, Wally Boswell and Ken Fraser, developed a working design that incorporated a fire-resistant and shockproof case, a reliable system for encoding and recording aircraft instrument readings and voice on one wire, and a ground-based decoding device. The ARL system, made by the British firm of S. Davall & Sons Ltd, in Middlesex, was named the "Red Egg" because of its shape and bright red colour. The units were redesigned in 1965 and relocated at the rear of aircraft to increase the probability of successful data retrieval after a crash.

Red Egg

Carriage of data recording equipment became mandatory in UK-registered aircraft in two phases, the first for new turbine-engine public transport category aeroplanes over 12,000 lb in weight was mandated in 1965, with a further requirement in 1966 for piston-engine transports over 60,000 lb, with the earlier requirement further extended to all jet transports. One of the first UK uses of the data recovered from an accident aircraft was that recovered from the Roystan "Midas" data recorder that was onboard the British Midland Argonaut involved in the Stockport Air Disaster in 1967.

Stockport Air Disaster

The "Flight Recorder" was invented and patented in the United States by Professor James J. "Crash" Ryan, a professor of mechanical engineering at the University of Minnesota from 1931 to 1963. Ryan's "Flight Recorder" patent was filed in August 1953 and approved on November 8, 1960 as US Patent 2,959,459. A second patent by Ryan for a "Coding Apparatus for Flight Recorders and the Like" is US Patent 3,075,192 dated January 22, 1963. An early prototype of the Ryan Flight Data Recorder is described in the January 2013 Aviation History Magazine article "Father of the Black Box" by Scott M. Fisher.

Professor James J. "Crash" Ryan

Ryan, also the inventor of the retractable safety seat belt now required in automobiles, began working on the idea of a flight recorder in 1946, and invented the device in response to a 1948 request from the Civil Aeronautics Board aimed at establishing operating procedures to reduce air mishaps. The requirement was for a means of accumulating flight data. The original device was known as the "General Mills Flight Recorder".

General Mills Flight Recorder

The benefits of the flight recorder and the coding apparatus for flight recorders were outlined by Ryan in his study entitled "Economies in Airline Operation with Flight Recorders" which was entered into the Congressional Record in 1956. Ryan's Flight Recorder maintained a continuing recording of aircraft flight data such as engine exhaust temperature, fuel flow, aircraft velocity, altitude, control surfaces positions, and rate of descent.

A "Cockpit Sound Recorder" (CSR) was independently invented and patented by Edmund A. Boniface, Jr., an aeronautical engineer at Lockheed Aircraft Corporation. He originally filed with the US Patent Office on February 2, 1961, as an "Aircraft Cockpit Sound Recorder". The 1961 invention was viewed by some as an "invasion of privacy". Subsequently Boniface filed again on February 4, 1963 for a "Cockpit Sound Recorder" US Patent 3,327,067 with the addition of a spring-loaded switch which allowed the pilot to erase the audio/sound tape recording at the conclusion of a safe flight and landing.

Boniface's participation in aircraft crash investigations in the 1940’s and in the accident investigations of the loss of one of the wings at cruise altitude on each of two Lockheed Electra turboprop powered aircraft led to his wondering what the pilots may have said just prior to the wing loss and during the descent as well as the type and nature of any sounds or explosions that may have preceded or occurred during the wing loss.

His patent was for a device for recording audio of pilot remarks and engine or other sounds to be "contained with the in-flight recorder within a sealed container that is shock mounted, fireproofed and made watertight" and "sealed in such a manner as to be capable of withstanding extreme temperatures during a crash fire". The CSR was an analogue device which provided a progressive erasing/recording loop of all sounds (explosion, voice, and the noise of any aircraft structural components undergoing serious fracture and breakage) which could be overheard in the cockpit.

Future technology

The disappearance of Malaysia Airlines Flight 370 demonstrated the limits of the contemporary flight recorder technology, namely how physical possession of the flight recorder device is necessary to help investigate the cause of an aircraft incident. Considering the advances of modern communication, technology commentators called for flight recorders to be supplemented or replaced by a system that provides "live streaming" of data from the aircraft to the ground.

Honeywell Aerospace took up the challenge and are developing the “black box in the sky” a.k.a. the Honeywell Connected Recorder (HCR-25). It will let airlines access flight data and cockpit voice recordings during flight. The recorder uses a secure, cloud-based satellite link to send data from the aircraft to a data centre using their software. There it can be analysed and maintained.

If an incident occurs, flight data can be quickly accessed by the airlines and investigators in real time. Key information will be available even before the black box is found. Investigators will be able to locate the site almost immediately and will have faster access to information that will help them understand events leading up to the accident.

The recorder collects data on thousands of variables including fuel levels, altitude, engine performance, temperature, direction and speed, which operators can use to improve operational and maintenance efficiency.

The HCR-25 represents a leap forward in this technology. It will include several innovations and meet the new European Aviation Safety Agency cockpit voice recording mandate, which takes effect in 2021 and requires a 25-hour voice recording capability.


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