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Backgrounder: Flight recorders

The International Civil Aviation Organization (ICAO) requires large commercial aircraft to carry 2 flight recorders: a flight data recorder (FDR) and a cockpit voice recorder (CVR). The FDR records parametric data for at least the last 25 hours of operation. The CVR records the flight crew’s communications and the aural environment of the cockpit for the last 2 hours of operation. Some newer flight recorders combine the functions of the FDR and CVR into a single unit. These units are referred to as cockpit voice and data recorders (CVDR) or combination recorders.

Although flight recorders are commonly referred to as “black boxes,” they are actually orange, which makes them easier to find at a crash site.

Technical standard for crash-protected flight recorders

The international technical standard for crash-protected flight recorders is document ED-112A, Minimum Operational Performance Specification for Crash Protected Airborne Recorder Systems, published by the European Organization for Civil Aviation Equipment (EUROCAE) in September 2013. According to the standard, flight recorders must meet the following crash survivability standards:

Each flight recorder must have an underwater locator beacon (ULB). The ULB activates when the recorder is immersed in water and transmits a signal for 90 days to help locate the flight recorder.

Flight data recorders

FDRs are required to record a minimum of 88 parameters, but most modern aircraft are equipped with models that record significantly more data than that. For example, the FDRs carried on new Boeing 737-800 aircraft record over 1500 parameters, and those carried on Airbus 380 aircraft record more than 2800 parameters.

Cockpit voice recorders

CVRs record 4 audio channels: the pilot microphone, the co-pilot microphone, an extra channel for other crew, and the cockpit area microphone (CAM). The first 3 channels record crew conversations and radio transmissions. The CAM records aural warnings and alerts, as well as the aural environment of the cockpit..

Recovering recorded data

Flight recorder data is stored in solid state memory and manufacturers frequently use data compression techniques to store the data. Manufacturer-developed hardware and software are used to connect to and communicate with the recorder in order to download the data. Once the download is complete, the file containing the data is typically decompressed using the manufacturer’s software to produce usable audio and flight data files. Analysis of the audio and data files is then carried out using specialized software applications.

If a flight recorder is not damaged, downloading data from it is relatively straightforward, as long as the required equipment and software are available.

Damaged flight recorders

If the flight recorder has been damaged, additional procedures, equipment, and software are required to ensure the safe recovery of all recorded data. The solid state memory unit is removed and inspected for damage. Repairs to the memory unit may require replacing connectors, repairing circuit boards, or cleaning and drying.

Once the memory unit has been repaired, it is installed on a surrogate flight recorder chassis (of the same model as the damaged recorder) and normal download procedures are followed to obtain the data files.

If the solid state memory unit is severely damaged, it may be necessary to remove the memory chips and read each one using a chip reader. Once all memory chips have been read, the data must be reassembled using special information and software from the manufacturer.

In addition to having the required tools, equipment, technical information, and software, the safe recovery of data from damaged flight recorders requires personnel with significant expertise in data recovery and data analysis to do the work.