Obviously, black boxes gather lots of media attention after tragic accidents where planes crash or explode mid-flight, since they could be crucial understanding the crash.

However, these are rather uncommon events.

Surely the black box could be used for other purposes like:

  1. Helping the pilots understand a small mistake/hiccup/etc. on their flight
  2. Monitor the plane's overall health
  3. ???

How often and for what purpose is black box data used?

  • $\begingroup$ Many data systems that might or will be used as evidence in a legal proceeding have to be used and treated in special ways or else their legal value is compromised. This extends far beyond "black boxes", but since CVRs and FDRs are expressly designed for investigation and legal action of some sort is extremely likely in the event of a crash, the forensic integrity of the data contained in them should be designed in from the start. Even read-only access can be considered to reduce forensic integrity in some situations. $\endgroup$ Commented Jun 20, 2016 at 17:44
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    $\begingroup$ You forgot 4. PROFIT $\endgroup$
    – Dan Hulme
    Commented Jun 21, 2016 at 7:45
  • $\begingroup$ @DanHulme which is accurate in this case ! $\endgroup$
    – Antzi
    Commented Jun 21, 2016 at 7:52
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    $\begingroup$ Monitoring plane's overall health is mainly done over ACARS. This transmits any fault indications over radio so the maintenance can have appropriate spare parts ready when the plane lands. Engines also similarly transmit data to the manufacturer. $\endgroup$
    – Jan Hudec
    Commented Jun 22, 2016 at 18:47

3 Answers 3


There are two recorders that are mandatory on board commercial aircraft: CVR for voice, and FDR for data. They are designed to survive an accident and include an ultrasonic beacon to facilitate locating them underwater.

enter image description here

It's worth mentioning that CVR and FDR are not connected to any external data port for data export/copy/extraction, and extraction of the recorders after an accident is done exclusively by the investigating agency.

(As everybody knows for years, these recorders are orange, so there is no need for journalists to continue to call them 'black boxes' as if we were not in the secret too and may not get what they are talking about...)

Cockpit voice recorder (CVR)

The CVR is a sensitive question. Crews have accepted the recording of cockpit conversations to help understand accidents. One condition is the conversations remain private in other circumstances. So there is definitely no other allowed use of the CVR.

Flight data recorder (FDR)

Certain technical parameters, like inputs on the flight controls, must be recorded, also to help determine the cause of an accident. Most FDRs record many more parameters than mandatory. Still the FDR cannot be used in other circumstances than an investigation (see section about data privacy further down).

Using in-flight data for improvement

FDR data causes less privacy concerns than CVR conversations. Safety agencies over the world have encouraged airlines and manufacturers to set up improvement programs (quality improvement) taking into account in-flight technical parameters.

diagram showing improvement cycle information flow

Quality improvement initiatives include:

FDM allows companies to:

  • Compare their flight standards (SOPs) and the crews' actual actions. This is a way to enforce SOPs, and detect deviations from SOPs, hence crews may be reluctant to see this becoming mandatory.

  • Detect excessive forces applied to the aircraft, that require maintenance checks and/or repairs.

  • Set fuel consumption improvement actions.

As the FDR data cannot be exported, new recorders used for data monitoring and analysis are now seen on aircraft.

Quick access recorders (QAR)

Quick access recorders (QAR) are used in place of FDR, they allow much freedom, they don't have the same use and disclosure restrictions, don't have to resist a crash and can be included in wireless networks. For example this is Wifi/Ethernet QAR:

enter image description here

QAR use the same data acquisition unit (DFDAU) as the FDR, using ARINC 573/717 links. They are essentially duplicating and extending the mandatory FDR, but data can be read at any time using data links. This access is not limited to investigation purposes.

Optical quick access recorders (OQAR) are QARs storing data on optical disks (e.g. Curtis-Wright), and they can record up to weeks or months of flight data. On the other hand, very small "micro" QARs exist too. This well known one uses a CompactFlash card:

an OQAR with a CF card inserted

Countries like India have mandated flight data monitoring and analysis using such devices, but most regulation bodies have taken into account the reluctance of crews regarding the spreading of sensitive data, and the programs remain subject to airline decision.

Privacy aspects of CVR and FDR data

This section is likely very incomplete as the topic is complex.


  • Investigation-related recommendations are described in Annex 13 to the Chicago Convention on International Civil Aviation: Aircraft Accident and Incident Investigation.

    Non-disclosure of records. 5.12 The State conducting the investigation [...] shall not make the following records available for purposes other than accident or incident investigation, unless the appropriate authority for the administration of justice in that State [...]: [...] b) all communications between persons having been involved in the operation of the aircraft; [...] d) cockpit voice recordings and transcripts from such recordings; 5.12.1 These records shall be included in the final report [...] only when pertinent to the analysis of the accident or incident. Parts of the records not relevant to the analysis shall not be disclosed.

  • Flight recorder cover both voice and data:

    Flight recorder. Any type of recorder installed in the aircraft for the purpose of complementing accident/incident investigation.

    However only CVR is mentioned in the article above, so there is some ambiguity about using FDR data.

  • The point about privacy is that if the information is disclosed, then the safety agencies may not be trusted in the future, information may not be provided, and security may suffer from this lack of information.

CVR in the US:

  • A CVR committee usually consisting of members from the NTSB, FAA, operator of the aircraft, manufacturer of the airplane, manufacturer of the engines, and the pilots union, is formed to listen to the recording. This committee creates a written transcript of the CVR audio to be used during the investigation.


  • Congress has required that the Safety Board not release any part of a CVR audio recording.

    (Source: ibid.).

  • Read also: "Privileged communications?" The bright line rule in the use of cockpit voice recorder tapes.

Recordings in EU:

  • Article 14, Protection of sensitive safety information in 996/2010:

    the following records shall not be made available or used for purposes other than safety investigation, or other purposes aiming at the improvement of aviation safety: (a) all communications between persons having been involved in the operation of the aircraft; [...]. Flight data recorder recordings shall not be made available or used for purposes other than those of the safety investigation, airworthiness or maintenance purposes, except when such records are de-identified or disclosed under secure procedures.

    • The article above covers both CVR and FDR, but seems less restrictive than the ICAO.
  • Article 34 in 76/2014:

    In order to ensure the confidence of employees or contracted personnel in the occurrence reporting system of the organisation, the information contained in occurrence reports should be protected appropriately and should not be used for purposes other than maintaining or improving aviation safety.

  • Reading the many CVR transcripts available online, it's obvious that this rule has sometimes been transgressed. Authorities have now difficulties when making the proposition to increase the legal duration of the recordings from 2 to 24 hours.

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    $\begingroup$ You indicate that the CVR & FDR data cannot be used except in an accident/incident investigation. Is that specific to certain country's regulations, or is that an ICAO standard that all countries have accepted? $\endgroup$
    – FreeMan
    Commented Jun 20, 2016 at 12:59
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    $\begingroup$ excellent! I'd give you another +1 for the update, if I could. $\endgroup$
    – FreeMan
    Commented Jun 20, 2016 at 14:53
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    $\begingroup$ I believe aircraft operators are required to regularly read FDR data as part of the operational checks mandated by the regulatory authorities to ensure the FDR is functioning. They have to use this to check that recorded sensor values are correct. This suggests they have the technical means to read FDR data for other purposes. $\endgroup$ Commented Jun 21, 2016 at 9:29
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    $\begingroup$ @Aron - just because something doesn't have a USB port doesn't mean data can't be extracted from it on a somewhat regular basis. I asked mins to clarify his statement that the data cannot be used except in an incident investigation, and he did so quite admirably. A USB port, or lack thereof, has nothing to do with the regulations around when data can be used from a data collection device. $\endgroup$
    – FreeMan
    Commented Jun 21, 2016 at 11:58
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    $\begingroup$ "there is no need for journalists to continue to call them 'black boxes' " Black is not a reference to their color. The name is used because they are write-only storage, only accessible to investigators. I.e. the user has no idea what goes on inside them. $\endgroup$
    – Hobbes
    Commented Feb 7, 2019 at 18:46

Addressing just your first item, the purpose of the cockpit voice recorder is to provide a record of all sounds in the cockpit from the time the recording stops back to however long the recording loop goes for. It should be used for accident or incident investigation only. You don't want pilots modifying what they say (or passing notes or using hand signals) because they have to be concerned with usage of the recording for anything other than accident investigation. Pilots don't expect to crash, thus, secure in the knowledge that the CVR will not be looked at except as part of accident investigation, they are free to say what they will.

Some pilots are more paranoid than others, at least they used to be back in the 1990s. I occasionally flew with pilots who availed themselves of being able to erase the CVR after a flight. On 747-100/200 aircraft you could erase the CVR if the engines were shutdown, you were on APU or ground power, and the parking brake was set. You did it by pressing and holding a button next to the microphone on the pilots overhead console.

I'm aware of at least one third-world airline that used to use the CVR to check what pilots had been saying, not for training purposes but to find out what the attitudes of the pilots were toward the company. We were flying Hadj charters for them. One day one of our captains caught them trying to change out the CVR. He ordered the offending technician off the airplane, immediately notified our management of what had happened, and made sure every captain flying on the contract was aware of the situation. I was so angered that anyone would try that kind of crap that for the next several days if any of their people came into the cockpit, I in no uncertain terms informed them that by U.S. rules (and we were in a U.S. registered airplane having to operate under U.S. rules) the CVR was to be used for accident investigation, not for spying on pilots.

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    $\begingroup$ Can they be used only for accident investigation, or for incident investigation too? I believe it is the later, i.e. that investigators can (and do) come for the recorders after events like serious traffic conflicts even though all the planes landed safely, nobody was hurt and nothing damaged. $\endgroup$
    – Jan Hudec
    Commented Jun 20, 2016 at 9:43
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    $\begingroup$ The CVR can also supply useful information in the recorded sounds in the cockpit; alarms, voice warnings, engine noise... $\endgroup$
    – DJohnM
    Commented Jun 20, 2016 at 15:33
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    $\begingroup$ @JanHudec I don't know the answer to that, but as it's obviously safety related, it would seem reasonable to allow that. $\endgroup$
    – Terry
    Commented Jun 20, 2016 at 17:10
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    $\begingroup$ @JanHudec: From Chicago Convention Annex 13: "5.7 Effective use shall be made of flight recorders in the investigation of an accident or an incident. The State conducting the investigation shall arrange for the read-out of the flight recorders without delay." Chapter 5.16 ensures this applies whatever the "State of Occurrence". $\endgroup$
    – mins
    Commented Jun 21, 2016 at 6:35

When are black boxes used? / How often and for what purpose is black box data 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.

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

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.”

My emphasis.

Daily checks

It is easy to find airline checklists that specify that the FDR is to be tested (e.g. Emirates 777 Freighter, p5)

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.


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.


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