Is the raw data fetched from the FDR available only in binary format and if so what are the software tools that are used to convert it to readable format?
FDR data, today, are recorded in solid state memory. Magnetic tape recorders cannot be used anymore since 2016.
International recommendations (ICAO Convention, annex 6) states:
126.96.36.199 In approving the means to make flight recorder data available in a timely manner, the State of the Operator shall take into account the following:
a) the capabilities of the operator; b) overall capability of the aeroplane and its systems as certified by the State of Design; c) the reliability of the means to recover the appropriate CVR channels and appropriate FDR data; and d) specific mitigation measures.
Note.— Guidance on approving the means to make flight recorder data available in a timely manner is contained in the Manual on Location of Aircraft in Distress and Flight Recorder Data Recovery (Doc 10054).
No mandatory data format is provided, but each country must ensure in its regulations that the description of the format is available to any agency involved in FDR readout. E.g. for the US in FAR 125.226:
Documentation sufficient to convert recorded data into the engineering units and discrete values specified in the applicable appendix must be maintained by the certificate holder.
The description of the data frame layout encompasses:
- The origin of the recorded parameter, and any computation done
- The method used for parameter calibration
- The method used to encode the value of the parameter
- The unit used.
- The method to be used to convert recorded values into readable values.
In spite of this, there are cases where information is missing, e.g. BEA, the French investigation agency noted for a case:
The operator was not able to provide the BEA with any data frame layout documents. A list of recorded parameters and their allocation in the data frame was obtained, but the conversion equations and the calibration reports were missing. The FDR data could not be analyzed.
(Flight Data Recorder Read-Out, §188.8.131.52)
In the same document you may read other cases where the FDR data readout has been difficult or impossible.
Data are recorded in any efficient format, generally not a user readable format. Data are compacted as much as possible to save memory requirements and volume, because this memory has to be protected against the effect of an accident, which can be expensive.
Readout is done using simple hardware/software. Many vendors have read/analysis suites. Exemple:
Other readout solutions:
You can see the FDR itself is used for the readout. In case the FDR unit is broken (which is frequent after accidents), the protected memory unit is extracted and read with another working FDR. Extraction of the memory module protected in temperature resistant foam:
(Source: ATSB accident report)