French ships equipped with US listening devices are ending their hunt for the black boxes of an airliner lost over the Atlantic on 1 June, officials say.

They failed to pick up signals the boxes’ "pingers" were meant to emit for 30 days after the Air France jet crashed with the loss of all 228 lives.

Experts believe the cause of the crash may never be known unless the two flight recorders are recovered.

There is still a chance that French submarines may discover the boxes.

See a map of the plane’s route

Brazil ended its operation to recover bodies and wreckage from Flight AF447, which was flying from Rio de Janeiro to Paris, towards the end of last month, after finding the remains of 51 people.

French investigators believe the plane, which disappeared in a storm, broke up on contact with water, not in the air.

They say the plane’s speed sensors appear to have been a factor in the crash but not its cause.

‘Still hope’

Two tugs chartered by the French agency investigating the crash (the Investigation and Analysis Bureau, or BEA) had been searching for the jet’s cockpit voice and flight data recorders with Towed Pinger Locators (TPL) supplied by the US Navy.

US Air Force Col Willie Berges, the Brazil-based commander of US military forces supporting the effort, said one tug had already stopped searching.

"The last ship will be departing the search area today," he told the Associated Press news agency on Friday, adding that he did not know the exact time.

The ships had had "no success – nothing was tracked", Col Berges said.

A French nuclear submarine, the Emeraude, has also been hunting the boxes and robot submarines will join the search later in July, Air France-KLM director Pierre-Henri Gourgeon said in an interview published in France’s Le Figaro newspaper on Thursday.

"All hope is not lost," he said.

Chief BEA investigator Alain Bouillard said last week that a French boat equipped with two small submarines would begin a search along with another submarine and a robot craft "after 14 July", a public holiday in France.

Friday saw the funeral in Dublin of a young Irishwoman who was aboard the jet along with two friends, all three of them doctors.

The body of Dr Jane Deasy was identified this month. Those of her friends, Dr Aisling Butler and Dr Eithne Walls, were never found.

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