> **When are black boxes used?**

- Recording
- Reading
  - Accident investigation
  - Operational testing
     - Annual
     - Daily
  - Other purposes

Used for recording data
===

The FDR and CVR are obviously in-use, for recording data, when the aircraft is being used to transport passengers or cargo.


Used for reading data
===

In the event of an accident
---

As we all know, after an incident, the recorders are used by the investigators to retrieve the data that has been recorded prior to and during the incident.


For operational testing
---

There is no point having a recorder installed if it is not working. This means that the recorder must be used for operational tests.



###Annual checks

The regulatory bodies have varying [rules for testing of recorders](https://www.flightdataservices.com/fdm-foqa-products-services/fdr-replay-and-readout/regulations/).

Here is an extract from ICAO regulations

> 6.10.10 Flight recorders — continued serviceability Operational 
checks and evaluations of recordings from the flight data and
cockpit voice recorder systems shall be conducted to ensure the
continued serviceability of the recorders.

> Attachment D - 3.2 : Annual inspections should be carried out as
> follows: 
>   a) the read-out of the recorded data from the FDR and
>      CVR should ensure that the recorder operates correctly
>      for the nominal duration of the recording; 

>   b) the analysis of the FDR should evaluate the quality of
>      the recorded data to determine if the bit error rate is
>      within acceptable limits and to determine the nature and
>      distribution of the errors; 

>   c) a complete flight from the FDR should be examined in
>      engineering units to evaluate the validity of all recorded
>      parameters. Particular attention should be given to  
>      parameters from sensors dedicated to the FDR. Parameters
>      taken from the aircraft’s electrical bus system need not
>      be checked if their serviceability can be detected by other     
>      aircraft systems;

The French investigation body "BEA" [state](https://www.bea.aero/uploads/tx_scalaetudessecurite/use.of.fdr_01.pdf)

> 2.1.5 Information on US regulations

> Regulations concerning FDRs in the United States are prescribed in FAR (Federal
Aviation Regulations), Part 125 – “Certification and Operations of airplanes which
have a seating capacity of 20 or more passengers or a maximum payload capacity
of 6,000 pounds or more,” section 125.226. Aircraft operators are required to
establish a method of readily retrieving data and to maintain documentation
sufficient to convert recorded data into engineering units (in data frame layout
documents). However, a single document may be established for any group of
aircraft that are of the same type and on which the flight recorder system and its
installation are the same.

> In addition, the FAA’s HBAW (Handbook Bulletin for Airworthiness) 97-13B of 15
December 1997 provides Principal Avionics Inspectors (PAI) with guidance
needed to evaluate FDR maintenance programmes. In particular, PAI’s should
check if the data frame layout documents are kept up to date and any
modifications/retrofits to DFDR systems are documented and accounted for.
Furthermore, it is stated that, **“PAI action should include air carrier operator
readout of each airplane’s DFDR to determine that all required parameters are
being recorded, and to verify that each parameter is working properly.”** 

###Daily checks

It is easy to find airline checklists that specify that the FDR is to be tested (e.g. [Emirates 777 Freighter, p5](https://egcexternal.emirates.com/filegac/engineering%20procedures/approvedforms/Attachments/QAF0480.pdf))

I don't know what form this test takes, perhaps there is some sort of quick self-test capability built into at least some recorders?

---

Other Purposes
-------

>**Surely the black box could be used for other purposes?**

###Cockpit Voice Recorders

Note that there are regulations preventing other uses of cockpit voice recorders specifically. *Federal CVR nondisclosure laws (refer to 49 United States Code (USC) Section 1114(c) – Disclosure, availability, and use of information*


###Flight Data Recorders

This is a subject that has been looked at in the past by academics. 

[FLIGHT DATA PROCESSING - TECHNIQUES TO IDENTIFY UNUSUAL EVENTS](https://theses.lib.vt.edu/theses/available/etd-06222000-11480046/unrestricted/phd.pdf) begins

> Modern aircraft are capable of recording hundreds of parameters during flight. This fact not
only facilitates the investigation of an accident or a serious incident, but also provides the
opportunity to use the recorded data to predict future aircraft behavior. It is believed that,
by analyzing the recorded data, one can identify precursors to hazardous behavior and develop
procedures to mitigate the problems before they actually occur. 

Instead, I believe airlines, and their partners, use ACARS transmissions, Quick-Access recorders and other methods of collecting data.