Fugro, which was contracted by the Australian government to operate three ships pulling sonar across the vast 60,000-km search zone, has rejected claims it is using the wrong equipment, saying its gear is rigorously tested.  Still, Nargeolet's concerns are echoed by others in the tightly held deepsea search and rescue industry, who are worried that unless the search ships pass right over any wreckage the sonar scanning either side of the vessels won't pick it up.  Experts also question the lack of data released by the Australian Transport Safety Bureau (ATSB) on the activities of the Fugro ships.  Three of the bidders rejected for the MH370 contract, U.S. firm Williamson & Associates, France's ixBlue SAS and Mauritius-based Deep Ocean Search Ltd, have taken the unusual step of detailing their concerns - months down the track - directly to Australian authorities in correspondence viewed by Reuters.  Several other experts are also critical, including some who requested anonymity, citing the close knit nature of the industry which has just a few companies and militaries capable of conducting deepwater searches.  Read MoreMalaysia Airlines: One year after MH370  "I have serious concerns that the MH370 search operation may not be able to convincingly demonstrate that 100 percent seafloor coverage is being achieved," Mike Williamson, founder and president of Williamson & Associates told Reuters.  Australia took over the search for the missing plane from Malaysia in late March last year, three weeks after MH370 disappeared off the radar during a flight from Kuala Lumpur to Beijing.  The search area was determined by satellite data that revealed the plane turned back sharply over the Malaysian Peninsula and flew undetected for another six hours before crashing into the inhospitable southern Indian Ocean.  The unchartered waters, buffeted by the Roaring Forties winds, stretch as deep as 6 km, hiding old volcanoes and cliffs in their depths. Australia, Malaysia and China earlier this month agreed to double the search area to 120,000 sq km.  Whether Phoenix International, which has U.S. navy contracts and found AF447, will be part of that extended search area is unclear after the ATSB said that Go Phoenix, owned by Australian firm Go Marine, will cease operating on June 19. Phoenix International, which was contracted separately by the Malaysian government, did not immediately return calls about its position. The Malaysian government also did not reply to requests for comment.  Two of the Fugro ships traverse up and down 2.4 km-wide strips of the sea floor, pulling via a cable a "towfish" that contains sonar equipment, in a technique often called "mowing the lawn".  The towfish coasts around 100 meters above the sea floor, sending out sound waves diagonally across a swath, or broad strip, to produce a flattened image of the seabed.
Nearly a year after the disappearance of MH370, authorities and search teams are being criticized over their search approaches.