Each time an aviation accident occurs, the media talk about the black box. This is always presented as kind of a magic tool to solve all issues with the investigation. As I already mentionned in previous posts about the TAM crash in Sao Paolo and others, life is not so easy, and I’d like to unveil some of the black-box mistery with this post.

First of all, there are two black-boxes, not one. The first one is the “Cockpit Voide Recorder”, and its name is quite self explanatory. It just records all voice communication, as well as cockpit noises. It can help to explain the human factor part of an accident.

The second one is the “Flight Data Recorder”, or more recently, “Digital Flight Data Recorder”, or DFDR. This one records several parameters, including but not limited to:
1) Air parameters (speed, altitude, …)
2) Aircraft configuration (flaps position, gear position, control column inputs, control surfaces position)
3) Engine parameters (power, pressures, temperatures, …)

Depending the type of operation and the number of seats of the aircraft, it can be mandatory or not to have CVR, FDR, or both. On modern airliners, there are also technical recorders, called “Quick Access Recorder”, or QAR, which are used by maintenance teams to monitor the technical status of the aircraft.

If you want to know more about FDRs, the french incident investigation burea produced a very good report about them, including details of their functionning, regulations, and some pictures.

Oh, and by the way, the black-boxes are orange, so as to be easier to locate for rescue / investigation teams. They are in protected cases, supposed to resist a crash, but it frequently happens that they get damaged. This was particularly true with the magnetic tape ones, where the tape tended to melt, or to be damaged by sea water.

It is also quite frequent to not have the very last seconds of recordings, because of communication failures between the aircraft and the recorder, in case the aircraft is broken up, or if electrical cables are damaged by overloads.

The analysis and transcription of black-box contents can be done only be certified and assermented officers.

To close this post, here is a link to the French air incident investigation bureau website, listing some other equivalent organisations. From here you can find many investigation reports. And please remind that these reports are the only one holding established facts. All the rest is journalist work as its best.