I am working with FDR readout data and I am trying to find good resources about measurement units for those logs. The data seems to be a mix of SI and non-SI units and it can be quite difficult to work with data if you don't have correct units.

The data comes from Boeing 757, 767 and 737MAX aircraft but I am not sure what type the FDR equipment is installed (will find out at some point).

Does anyone have a good resource on this?

I am using this data to create graphs and measurements in Elasticsearch and Kibana, focusing on fuel efficiency. It is quite interesting to see how fuel flow is different between engines and how altitude affects fuel consumption.

  • 2
    $\begingroup$ Have you tried referring to ARINC Characteristic 747-3, Flight Data Recorder? It should have the relevant information, though you may also need a copy of ARINC 429 to understand individual data parameters. $\endgroup$
    – Gerry
    Sep 13 '18 at 11:43
  • 5
    $\begingroup$ Whoever supplied the data should be able to supply what’s called a data frame description which explains how to translate the raw data into engineering units. It can be different across tailsigns even on the same type. $\endgroup$ Sep 13 '18 at 12:40
  • $\begingroup$ @Gerry, the spec of the FDR does not give the order of the recorded parameters except for the first words that concern the airplane identification. In arinc 429 the label gives the parameters, on the FDR we have only 12 bits words, the parameters order is not mandatorily the same $\endgroup$
    – user40476
    Jun 13 '19 at 9:08
  • $\begingroup$ @Cpt Reynolds, not necessarily, the DFR data, are similar to QAR data, some maintenance engineers might deliver recorded QAR data, without knowing their interpretation $\endgroup$
    – user40476
    Jun 13 '19 at 9:12
  • $\begingroup$ @user40476 Of course. The operator should be able to acquire and pass on the description though. It’s not necessarily listed in the AMM, by the way - none of my airline’s are. $\endgroup$ Jun 13 '19 at 10:16

According to the provisions in ICAO Annex 6 - Operation of Aircraft, Vol 1 and Vol. III, a Type I FDR shall record the parameters required to determine accurately the aeroplane flight path, speed, attitude, engine power, configuration and operation. Types II and IIA FDRs shall record the parameters required to determine accurately the aeroplane flight path, speed, attitude, engine power and configuration of lift and drag devices.

Therefore the listing word by word is not defined by the authorities


As a start, but not only, it depends on the age of the aircraft, for instance early 737 had 64 words of 12 bits, most of these words have the first 2 bits for binary states(open, closed, selected on or selected off, etc) the remaining bits are for an analog value expressed binary, such as pressure, speed, vario, etc. Some other words are fully for states conditions, that is every bit of the 12 bits of the word indicates a state.

To the opposite of early 737 late 737s have 256 words, So it doesn’t depend on the type of FDR, but on the specific model of aircraft, the type of FDR is just a consequence; 2 FDRs recording the same number of words won’t have the same words definitions

But more than that:

The FDR will record what it receives from a computer that centralizes all the data and that manages the data into 12 bits words. The recorded data depends on the chronology of received words. This chronology doesn’t depend on the FDR but on the emitting computer that sends the data to the FDR

But also

It depends on the specific options of the aircraft, that’s why every aircraft has its own listing, the investigation center will get this data either from the aircraft manufacturer or from the operator, because the data is also available in the specific maintenance manual of the aircraft.

So unhappily you have to refer to the maintenance manual of what, of the specific aircraft

Now a hint: if you find in the nature an FDR, how to decode it if you don’t know ahead to what aircraft it belongs?

  • Externally it has a serial number that will normally allow the required traceability

  • While reading the data frames the identification of the aircraft is recorded on the first words

Is this a general answer, may be yes. Am I giving the parameters of every recorded word, the answer is no; Am I giving the corresponding units? The answer is no; However I am telling where to find these, that is the specific maintenance manual of that specific aircraft. Had I to refrain from answering? May be no. Since 1 year, not to give a general answer nobody has answered. Nevertheless hope this has been helpful.


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