Accident investigators are searching for the aircraft's
black-box flight recorders
Such words are sometimes heard on TV news reports
about aircraft accidents...
Australia was one of the first countries to introduce this
requirement and today, all aircraft on the Australian register with
a maximum takeoff weight greater than 5,700 kg are required to
carry both a cockpit voice recorder (CVR) and a flight data
recorder (FDR).
These 'black boxes' are in fact painted orange to help in their
recovery following an accident. They are also fitted with
battery-powered sonar transducers to aid underwater recovery.
ATSB's central office in Canberra includes an audio laboratory
and an FDR laboratory. The principal purpose of the ATSB
laboratories is to perform CVR and FDR readouts for the
investigation of occurrences, both within Australia and overseas.
Australia is one of the only countries in the Asia-Pacific region
to have these laboratories and ATSB has offered its services to
overseas authorities to assist in the investigation of major
accidents. ATSB assists regional neighbours such as New Zealand,
Indonesia, Singapore, Taiwan and Bangladesh with investigation
readouts. The ATSB has read out and analysed the flight recorders
from:
- the A300B4-220 accident in Medan, Indonesia on 26 September
1997; and
- the A300B4-600R accident in Taipei on 16 February 1998.
Readouts are also carried out for certification of new
recorder-type/aircraft-type combinations.
In addition to its recorder readout capability, ATSB has
advanced computer graphics software which allows data obtained from
all available sources to be combined to create a graphical
reconstruction of the sequence of events in an accident or
incident. These sources include FDR, CVR, ground-based radar
recorders, eye-witness reports, ATS communications tapes and
wreckage analysis. Videos can also be produced from the computer
graphics workstation. Computer graphics is a powerful tool for
investigators, being an excellent means of explaining accident
scenarios to people unfamiliar with aviation, and also providing a
valuable educational tool for pilots and other aviation
professionals.
Example of a computer graphics animation. 'Chase plane'
view of a BAe146 landing...
If an accident occurred at night in a remote area or at sea, the
flight recorders may be the principal, if not the only, means of
establishing the sequence of events immediately preceding the
accident. At the very least, CVR and FDR data can save an
investigation team many days or weeks of delay as the team examines
the wreckage.
Many accidents have involved aircraft without flight recorders,
and despite thorough investigation, the factors underlying these
occurrences remain inconclusive or unknown. On the other hand,
accidents leaving very little recoverable aircraft wreckage have
been resolved once the flight recorders were found.
Flight recorders are also particularly useful for cases in which
evidence is transitory, e.g. occurrences involving windshear. In
such instances, flight recorders will reveal the sudden effects of
windshear upon an aircraft's flight path. The evidence available
from flight recording indicates that, prior to flight-parameter
recording, the effect of the wind in many aircraft accidents was
underestimated.
VH-IWJ Westwind 1124 accident
This aircraft crashed into the sea off Sydney shortly after
takeoff on 10 October 1985. It was completely destroyed on impact
and very little wreckage was found immediately after the accident.
Approximately three months later, the CVR and FDR were located on
the seabed and recovered. Analysis of both recorders at the
Bureau's laboratories in Canberra was crucial in determining the
factors underlying this accident. In particular, the CVR revealed
that the pilot in command was simulating emergency instrument
flight conditions during a check of the co-pilot and the FDR
revealed that a loss of control occurred at an altitude of 5,000
ft.
CVR partially dismantled showing protective tape
enclosure...
The requirement for the fitment of flight recorders to
Australian-registered aircraft is contained in Civil Aviation Order
CAO 20.18. The equipment standards are detailed
in CAO 103.19 and CAO 103.20.
Under the Transport Safety Investigation Act 2003 a
CVR is classified as an On-board recording (OBR). The term OBR is
used to describe a recording that consists of sounds and/or images
of persons in the control area of a transport vehicle. The other
requirements include:
- The recording was made in order to comply with a law in force
in any country (Presently the OBRs that are made to comply with a
law in Australia are Cockpit Voice Recordings (CVRs) in aviation
and in marine Voyage Data Recorders are required on some
Ships).
- Any part of the recording was made at the time of the
occurrence of an immediately reportable matter that involved the
transport vehicle.
ATSB has the statutory power under the Transport Safety Investigation Act 2003,
to take into custody and examine any OBR from an aircraft that has
been involved in a Transport Safety Matter.
As a flight recorder has a limited length recording cycle,
prompt action is required to quarantine any recorders after an
incident or accident to ensure that the data are not
overwritten.
Access to the information from a CVR is limited.
An investigation, due to its size and the expertise required,
may necessitate the allocation of more resources than are available
within the Bureau. In such cases, individuals from outside
organisations will form part of the investigation team. Outside
organisations may be represented on investigations in one of three
ways: accredited representative; participant; and observer. ATSB
grants accredited representatives the rights and privileges
expressed in the standards and recommended practices of the ICAO
Convention on International Civil Aviation - Annex 13, by allowing
accredited representatives to act as participants. Participants are
permitted to observe and participate in an investigation, with the
exception of the output of the CVR.
In the case of occurrences involving Australian registered
aircraft outside Australian territory, Australia will appoint an
accredited representative, normally an ATSB investigator. The
accredited representative may appoint advisers who will be
permitted access to data and information in accordance with the
provisions of ICAO Annex 13 Paragraphs 5.24 and 5.25 in so far as
is necessary to enable the accredited representative to make his or
her participation effective.
ATSB will advise flight crew members and their union
representative(s) when a CVR is to be used in an investigation. The
crew and their nominated representative(s) will be invited to be
present during the CVR replay and may be invited to participate in
the preparation of the CVR transcript. A complete or partial
transcript of a CVR recording will only be made by the investigator
in charge if he or she considers that such a document is essential
to an understanding of the occurrence. The investigator in charge
will endeavour to obtain the agreement of the surviving crewmembers
and their union representative(s) that the CVR transcript is
accurate.
The Executive Director of ATSB may if it is necessary or
desirable for the purposes of transport safety disclose the
information to any other person. However, in accordance with ICAO
Annex 13 Paragraph 5.12, the CVR transcript will only be used in
the final report when it is pertinent to the analysis of the
occurrence. Parts of the transcript not relevant to the analysis
will not be disclosed.
Confidentiality provisions are in the Transport Safety Investigation Act 2003 to
ensure the future free-flow of safety information. OBRs are
primarily installed on transport vehicles for safety purposes and
it is acknowledged that they constitute an invasion of privacy for
the operating crew that most other employees in workplaces are not
subject to. The confidentiality provisions recognise the context in
which OBRs are installed, which is to provide valuable safety
information to assist in determining the factors that relate to a
serious occurrence.
The Transport Safety Investigation Act 2003
strictly controls the use of OBR information to ensure it is not
used for inappropriate purposes. Unless it is otherwise permitted
by the Act, section 53 makes it an offence for any person to copy
or disclose OBR information. The Act also prevents the use of OBR
information against crew members in criminal proceedings and it
cannot be used against employees for disciplinary action. The use
of OBR information is also heavily restricted in civil proceedings.
Before OBR information can be disclosed or admitted in civil
proceedings the Executive Director must issue a certificate stating
the disclosure is not likely to interfere with any investigation.
This broad test means that it will be unlikely that OBR information
will be disclosed in civil proceedings. In the unlikely event of a
certificate being issued, the court must conduct a public interest
test under section 56 of the Transport Safety Investigation Act
2003.
The only exception to the foregoing is a coronial inquest where
an OBR must be divulged to a coroner where the coroner requests it
and the Executive Director believes the OBR will not have an
adverse impact on the investigation to which the OBR relates.
Note that a recording only becomes an OBR on the occurrence of
an immediately reportable matter. The Executive Director must issue
a declaration that the OBR is not to be treated as an OBR if the
ATSB does not investigate the immediately reportable matter. If the
Executive Director does decide to investigate the immediately
reportable matter to which the OBR relates and the Executive
Director is satisfied that any part of the OBR is not relevant to
an investigation then the Executive Director must declare that part
not to be an OBR.
If an OBR that is a CVR ceases to be an OBR then it will receive
the confidentiality protections of Part IIIB of the Civil Aviation Act 1988 (CA Act). Part
IIIB of the CA Act covers all CVRs that are not OBRs under the
Transport Safety Investigation Act
2003.
Copies of Annex 13 may be purchased from ICAO. Please visit the
ICAO website or
e-mail the ICAO Document Sales
Unit.
Most CVRs today are analogue recorders using magnetic tape as
the recording medium. Recently, solid-state CVRs in which the audio
information is sampled, digitised, recorded and transferred into
memory chips for storage, have become available.
Modern FDRs are mostly digital recorders using magnetic tape as
the recording medium. As with CVRs, solid-state FDRs are now
available in which the recorded and digitised data is stored in
memory chips
Solid-state digital flight data recorder
pictured...
Flight recorders are crash-protected to survive both high-speed
impact and post-impact fire. They are, however, sometimes
destroyed.
The data, rather than the recorder, must survive an accident.
The data storage medium (tape or microchips) is mounted inside an
impact and fire resistant container. The other components need not
survive and are mounted outside the container.
The crashworthiness standards of flight recorders have been
recently reviewed by the European Organisation for Civil Aviation
Equipment (EUROCAE) committee, an international body on which ATSB
was represented. The recorder's memory module is now required to
withstand an impact producing a 3,400-g deceleration for 6.5
milliseconds (equivalent to an impact velocity of 270 kts and a
deceleration or crushing distance of 45 cm) and then to withstand a
fire of 1,100 degrees C for 60 min.
Flight recorders are normally located near the aircraft's tail,
as experience has shown that this area generally suffers the least
damage during an accident.
Cockpit voice recorder as received by ATSB showing
accident damage...
The Cockpit Voice Recorder
The CVR would be better named the cockpit audio recorder as it
provides a record of the total audio environment in the cockpit
area. This includes crew conversation, radio transmissions, aural
alarms, control movements, switch activations, engine noise and
airflow noise.
The CVR retains the last 30 minutes of information on tape
operating on the endless-loop principle.
Approximately 80% of aircraft accidents involve human factors
which, in most cases, means crew performance was a factor.
Consequently, the CVR often assists accident investigators to
determine why an accident occurred.
The Flight Data Recorder
The FDR records flight parameters. The range and quantity of
data recorded varies widely, depending upon the age and size of the
aircraft.
The minimum requirement is to record a basic group of five
parameters:
- Pressure altitude
- Indicated airspeed
- Magnetic heading
- Normal acceleration
- Microphone keying.
Microphone keying (i.e. the time radio transmissions were made
by the crew) is recorded to correlate FDR data with CVR
information.
This basic requirement has existed since the 1960s, and today,
modern jet aircraft far exceed this basic requirement, being fitted
with FDRs that can record up to 400 parameters covering all aspects
of the aircraft operation.
The FDR retains the last 25 hours of aircraft operation on tape
and, like the CVR, operates on the endless-loop principle. As FDRs
have a longer recording duration than CVRs, they are very useful
for investigating both incidents and accidents.
The FDR often tells accident investigators what happened during
an accident sequence.
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| Type: |
Educational Fact Sheet |
| Publication Date: |
15/11/2000 |
