The French nuclear submarine Emeraude today joined the search off the coast of Brazil for Air France flight 447's flight recorders, which may help investigators understand why the Airbus A330 went down on May 31 with 228 people on board. A research vessel from the French Research Institute for Exploitation of the Sea is expected to arrive Friday carrying the Nautile mini-submarine and a remote-controlled robot called Victor 6000 to help locate the black boxes before they stop emitting locating signals, ABC News reports.

The Emeraude is expected to trawl 13 square miles (35 square kilometers) daily, using sonar to try to pick up the boxes' acoustic beacons, whose signals are expected to start fading 30 days after the crash, the Associated Press reports. The submarine will be reinforced by two U.S. underwater audio devices capable of picking up signals even at a depth of 20,000 feet (6,100 meters), according to the Associated Press.

The 26-foot (eight-meter) long Nautile, which is equipped with cameras and a panoramic sonar capable of detecting signals up to 656 feet (200 meters) to the side, made several dives to the Titanic in 1987, 1993, 1994, 1996 and 1998, including when the wreck was first discovered, the Associated Press reported last week. The mini-sub can carry up to three passengers in its 10-foot (2.1-meter) diameter cabin.

Without important information from the Airbus A330's missing data recorders, investigators have focused on problems with the aircraft's pitot tubes, a classic fluid dynamic sensor named for its inventor, Henri Pitot, who in the 18th century developed it to measure the speed of rivers and canals in France. Last week Airbus released a memo stating that "there was inconsistency between the different measured airspeeds" coming from different pitot tubes.

Mini-subs are also being used to study the Pacific's Mariana Trench (the deepest part of the ocean) as well as the Gulf Stream's temperature, salinity and water density. in April reported on different types of manned and unmanned submersibles, past, present and future.

Nautile images © Ifremer