A TEAM of self-propelling robots is to comb 800 square miles of the Atlantic ocean floor this month. It will be the third attempt to locate the wreckage of the only aircraft in the past 30 years of commercial aviation whose black box flight recorders have not been recovered after a crash at sea.

After delays caused by bad weather and technical problems, French investigators are spending $14m (£9.2m) on the search for the wreckage of Air France flight 447, an Airbus A330 that disappeared last June in thunderstorms 600 miles off Brazil.

The crash has been blamed on a build-up of ice on speed sensors known as pitot tubes, but officials say no firm conclusions can be drawn without cockpit data from the aircraft’s last moments.

Jean-Paul Troadec, France’s chief accident investigator, said his team had been able to narrow the search area using computer models of currents in the days after the crash, which killed all 228 people on board. “We’ve reduced the size of the haystack,” he said. “Now we have to find the needle.”

The search will be led by three 12ft robots known as autonomous underwater vehicles. Operating at depths of up to 13,000ft, the robots will cruise close to the mountainous sea bed, following its contours.

Without the black box data, investigators may never establish how the crew reacted to faulty airspeed readings as the aircraft encountered heavy turbulence at 36,000ft.

Investigators believe the frozen pitot tubes may have triggered automated shutdowns that knocked out the autopilot and engine control systems. Questions remain about the route taken by the pilot, Marc Dubois, whose plane was flying close to its maximum permissible weight. He may have been keen to avoid detours around storms.