Next month's renewed search for the wreckage of Air France flight AF447 will concentrate on a 20nm (37km) circle centred on the last known position of the aircraft.

The search, the fourth phase in the frustrated effort to locate the crashed Airbus A330, will be based on a sytematic examination of all areas not previously explored by acoustic imaging, says the French Bureau d'Enquetes et d'Analyses.

US-based scientific modelling specialist Metron has assisted with piecing together the results of the three previous searches since the loss of the aircraft in June 2009.

In an analysis of these searches, it states that the "large uncertainty" in the crash position and the difficulties of underwater search activity means the combined effort has "effectively searched only 58%" of the region under scrutiny.

This figure, it cautions, assumes that the locator beacons from the flight recorders were working after the impact. If they were damaged, or were not functioning, the detection probability drops to just 29%.

"This means substantial additional effort will be required to insure a high probability of success," it adds.

Metron has recommended that resources should be deployed to investigate specific targets identified by previous searches which were "suggestive of debris" but not examined, in order to "remove any doubts as to their nature".

It also states that one of the "major causes of uncertainty" in the location of the wreckage has been the "lack of good ocean current data" in the vicinity of the accident for the period 1-10 June 2009.

"Detailed and accurate knowledge of currents would have allowed us to perform a reverse-drift analysis that might have substantially reduced the uncertainty in the wreck location," it says, pointing out that the US Coast Guard typically deploys self-locating data marker buoys to provide good surface current estimates.

BEA states that the region of interest to the search team is a 40nm circle around the last known position of AF447, which was en route from Rio de Janeiro to Paris, and that the new search will begin with the innermost 20nm.

Source: Air Transport Intelligence news