Reports/The Operational Search for MH370/Initial priority search area

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Defining the initial underwater search area
Initial priority search area

On 28 April 2014, the Prime Minister of Australia announced that Australia, represented by the ATSB, would coordinate the underwater search for MH370. The ATSB subsequently formed and coordinated the Search Strategy Working Group (SSWG) to facilitate interaction with the Annex 13 investigation team flight path reconstruction group and satellite communications working group (SATCOM WG) to progress work on defining an initial underwater search area. The aim was to define underwater search areas along the 7th arc in the Indian Ocean where the SATCOM data indicated a power interruption close to the time of expected fuel exhaustion (Table 19).

An Inmarsat BFO model designated ‘Differential Doppler Analysis ECLIPSE_2’ was finalised in April 2014. This model incorporated all data frequency translations that Inmarsat were aware of at that time. The chronology and further information on doppler model development by Inmarsat is provided at appendix C.

Table 19: Initial priority search area

Dates: 14 June – 26 August 2014
Event: Mapping of seafloor in proposed underwater search area of 60,000 km 2
Search area location: Priority and medium search areas;
27.4⁰S to 32.1⁰S along 7th arc, -20 NM, +30 NM across 7th arc.
Search activity: Mapping of seafloor – bathymetry phase.
Guiding advice: Initially Inmarsat’s ‘Differential Doppler Analysis Eclipse 2’ BFO model was used to define priority, medium, wide search areas for 26 June 2014 report.
The unified model released on 19 June 2014 and subsequent revisions were used in flight path modelling developments after this date.
Data used in planning search area refinement: Effects of an eclipse on the satellite during a period of MH370 flight taken into consideration.

Refined EAFC model.
1912 NW point (8⁰ 35.719’N, 92⁰35.145’E) reassessed as invalid and no longer used by flight path reconstruction groups.
Flight path from 2nd arc at 1941.
Candidate paths with zero BTO tolerance.
Candidate paths within BFO tolerance of 10Hz.

Loss of control study, arc tolerance, balance of uncertainties and agreed area of 60,000km 2 results in width of +30 NM, -20 NM around 7th arc.
Search equipment: Fugro Equator (ATSB contract survey vessel, multibeam echo sounder (MBES))
Zhu Kezhen (the People’s Republic of China hydrographic survey vessel, MBES)
Coverage details: Approximately 38,000 km² completed in defined priority area 27.4⁰S to 32.1⁰S.
References ATSB report: MH370 – Definition of Underwater Search Areas – 26 June 2014

Source: ATSB

Inmarsat techniques applied to the model indicated best fit agreement for a 400 knot ground speed flight crossing the 2nd arc at latitude 2°N, ending at 28.2°S, 99.6°E at 0019 UTC. The model provided reasonable matches for a range of ground speeds between 375 and 500 knots from the estimated 2nd arc starting location, with the end-of-flight between latitudes 25°S and 37°S on the 7th arc.

Further flight path reconstruction techniques using this model were undertaken in May and June 2014 to define the initial underwater search area. The proposed underwater search area at that time was defined in ATSB report MH370 – Definition of Underwater Search Areas released on 26 June 2014. The application of the ‘Eclipse 2’ BFO model by the flight path reconstruction group had resulted in a shift of the most probable aircraft paths southwest along the 7th arc from the red/yellow/green area (latitudes 20.2°S–26°S) to an orange priority area (latitudes 27.4°S– 32.1°S).

The report defined priority, medium and wide search areas spanning increasing lengths along and widths across the 7th arc. The priority area for the underwater search defined in June was based on the area agreed by Tripartite governments of 60,000 km². This area was equal in size to the red/yellow/green search area defined during the surface search.

The underwater search areas were designated block numbers and width letters (Figure 26).The ‘A’ blocks were areas of 10,000 km² each. The priority search area was therefore defined as Blocks 1A–6A.

Figure 26: The underwater search area, June 2014 (not included here)

A reasonable search width for a ‘loss of control’ end-of-flight scenario was determined to be 30 NM in front and 20 NM behind the 7th arc. These were the limits of the A blocks. These widths allowed an approximate search area length of 650 km along the 7th arc (orange coloured area) for a total area of 60,000 km 2 .

Source: The Operational Search for MH370, Australian Transport Safety Bureau, 3 October 2017

Extracts from The Operational Search for MH370 have been included here for reference purposes, particularly the sections which relate to the history of the flight; times and events; the aircraft's satellite data unit (SDU); and the Pilot in Command’s flight simulator.