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salinity and the temperature of the water, must also be taken into account. When an acoustic
wave is propagated in the sea, it is subjected to refractions and this generates multiple
trajectories. The acoustic waves may also be deflected in such a way that there is a
"shadow" region which is never reached by these waves.
Acoustic searches using beacons which transmit at 37.5 KHz (± 1 KHz) are in general more
effective than searches using sonar, magnetometers and video cameras. Nevertheless, the
duration of the beacon transmission is limited, being certified for a minimum transmission
duration of thirty days from immersion.
Taking into account the range of the beacons, the hydrophones must be brought closer to
the source of transmission, by towing specialized equipment near the seabed.
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The underwater search devices that are used after localisation of the wreckage must also
take into account the depth and uncertainty of the area. In the case of the accident to flight
AF447, provision has been made for specialized devices able to descend to a depth of six
thousand metres.
1.16.1.3 Resources deployed by France
By the Ministry of Defence
The French Navy deployed the frigate Ventôse and the Mistral BPC (projection and
command ship), which have been taking part in the search and recovery operations for the
floating bodies and debris. They have been assisted by their on-board helicopters and Naval
Aviation and Air Force planes.
The Emeraude (hunter killer nuclear submarine) was sent to the area to complete the
acoustic search system.
Ventôse frigate SNA Emeraude BPC Mistral
By the BEA
In relation to towed acoustic devices, the BEA approached the US Navy. The latter has two
towed pinger locator (TPL) hydrophones and uses them regularly to search for civil or military
aircraft crashed at sea.
The US Navy TPLs can operate at up to a depth of six thousand metres. They operate on a
waveband between 5 and 60 KHz which includes the frequency transmitted by the
underwater locator beacons. The average detection range of the TPLs is estimated at two
kilometres at least.
To optimize the use of this equipment, the BEA chartered two available ships from the Dutch
subsidiary of Louis-Dreyfus Armateurs. These two tugs are the "Fairmount Expedition" and
the "Fairmount Glacier".
The BEA also chartered the oceanographic ship "Pourquoi Pas ?" from IFREMER together
with its specialized exploration and intervention resources, the "Nautile" submarine and the
“Victor 6000” ROV, which are able to operate at a depth of up to six thousand metres. These
vehicles can also map the site of the accident.
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The "Pourquoi Pas?" has acoustic detection equipment on board:
• an acoustic Repeater,
• a SMF (multi-beam sonar) modified to operate in passive mode,
• "ROV homer" directional hydrophones, which can be adapted to the underwater intervention
resources.
1.16.1.4 Organisation of the underwater searches
Before the tugs and the submarine arrived at the estimated site of the accident, a grid
network was made for the search area at the CECLANT centre in Brest by the French Navy
and the BEA. The area was thus divided into blocks with sides measuring ten arc-minute
lengths (that is to say squares with sides measuring approximately 10 NM at these latitudes,
see figure in 1.16.1.1). In most of these blocks, depths can exceed 3,500 m. The working
areas were distributed between the surface ships and the underwater resources so that the
search was carried out rapidly under good safety conditions.
The tactical coordination of the searches takes place on board of the "Pourquoi Pas?". It is
being conducted by the BEA together with the CEPHISMER personnel (French Navy).
The SHOM detachment on board the "Pourquoi pas?" is working to improve the knowledge
of the topography of the area. The deep sea multi-beam probe can be used to collect depth
data. Current measurement data and data related to the measurement of the speed of sound
in the water are also being processed.
In order to use the towed pinger locators, they are towed at approximately three knots as
close as possible to the seabed. In order to systematically cover the area, the tugs use lines
with a spacing of 2.5 km. This takes into account the scan swath of the TPL which is
approximately 2 NM.
1.16.2 ACARS messages
1.16.2.1 ATC messages
No ATC messages were received or transmitted by F-GZCP. Only three attempts were made
to connect up to the Dakar centre ADS-C system and were recorded on 1st June at 1 h 33,
1 h 35 and 2 h 01. The three requests were refused with a FAK4 code, meaning that the
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