BryceM - Pinger Life:
Orchestrating a search of this type would not be simple: you're forced to use a bunch of vessels of opportunity, most of whom know nothing about survey techniques, don't have software which allows them to easily plot and run survey lines, may not have survey grade (D)GPS, aren't familiar with the requirements of an acoustic survey, don't have a common means for sharing information, etc. Well-meaning but inept, in all probability. (That's not meant to be offensive - these things are more complicated than they first appear, is all).
Actually, it is not the case. The means (vessels and crews) employed are trained for the job and equipment/communications and softwares are not lacking. They already have been used and succesfully recoved orange boxes in the past:
LOUIS DREYFUS ARMATEURS has been working in close cooperation with the BUREAU d'ENQUÊTES et d'ANALYSES (BEA) since Monday 1st June as soon as the accident was announced.
LDA crews and teams have already demonstrated their skills in similar operations with :
- the recovery of the two flight recorders from the Boeing plane that crashed near Sharm El Sheikh in 2004. They were found by more than 1,000 meters depth.
- the recovery of the flight recorder from the Air Moorea plane that crashed in 2007. The black box was found by around 650 meters depth.
Louis Dreyfus Armateurs
Fairmount Glacier & Fairmount Expedition (reinforced by USN/CG team operating the TPLs):
And the oceanographic vessel of Genavir (IFREMER/Marine Nationale) "Pourquoi Pas?" which is used as GQG for the operation:
Descriptif du Pourquoi pas ?
(its in French but the technical description of the scientific equipment include 950 m² of command posts, laboratories, computer systems (including ultra short waves DGPS system, and so on)
About the organisation of the search, it is described in the BEA report:
1.16.1 Sea Searches
1.16.1.1 Context of the searches
The estimated area of the accident is over the Atlantic Dorsal Chain. The search is proceeding there in an unfavourable environment due to the depth and to the topography of the seabed. This seabed is little known and presents, over short distances, depths going from 900 metres to approximately 4,600 metres. The distance from dry land implies a lack of radar coverage and radio communication difficulties.
The search area was initially defined based on the airplane’s route and the last position contained in the ACARS messages. This makes an area with a radius of 40 NM, extending over more than 17,000 km2 and located more than 500 NM from the coasts.
The searches on the surface made it possible to locate bodies and airplane parts from 6 June onwards. The position of the floating elements allowed a search zone to be defined based on the work on the currents and the winds. The following figure shows the underwater search area.
1.16.1.2 Principle of the underwater searches
As the aircraft's recorders were each equipped with an underwater locator beacon, it was best to prioritise an acoustic search initially, nevertheless taking into account the limited range of the beacons, which is about two kilometres at most. The propagation of acoustic waves in a liquid medium, which depends on many interdependent parameters such as the 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. 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.
. 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.acoustic search system. 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.