CAIRO: Egypt has asked European firms to help search for the black boxes of an EgyptAir plane that crashed on May 19 in deep water in the Mediterranean Sea, the airline's chairman and French diplomatic sources said on Wednesday.

Nearly a week after EgyptAir flight 804 crashed with 66 people on board, including 30 Egyptians and 15 from France, investigators have no clear picture of its final moments.

EgyptAir chairman Safwat Musallam did not name the French and Italian companies involved but told a news conference they were able to carry out searches at a depth of 3,000 metres.

Two French diplomatic sources said Egyptian authorities and France's BEA air accident investigation agency were finalising a contract with two French companies, Mauritius-based Deep Ocean Search and Alseamar.

"The objective is to go extremely quickly so they can find the boxes that are probably in very deep waters," said one source.

The source said the costs of the contract would be shared between France and Egypt. Neither source was aware of talks with the Italian company.

The plane and its black box recorders, which could explain what brought down the Paris-to-Cairo flight as it entered Egyptian air space, have not been located.

The black boxes are believed to be lying in up to 3,000 metres of water, on the edge of the range for hearing and locating signals emitted by the boxes.

Maritime search experts say this means acoustic hydrophones must be towed in the water at depths of up to 2,000 metres in order to have the best chance of picking up the signals.

Until recently, aviation sources say, the US Navy or its private contractor Phoenix International were considered among the only sources for equipment needed to search on the correct frequency for black box pingers at such depths.

The US Navy said on Tuesday it had not been asked to help.

Batteries powering the signals sent from the black boxes typically last only 30 days, but EgyptAir's deputy chairman Ahmed Adel said the search would continue beyond then if necessary, using other means to locate the recorders.

"There are many examples in similar air accidents when 30 days passed without finding the box yet ... these planes' black boxes were found," he said.

'PLANE'S MACHINES WERE SAFE'

Musallam reiterated earlier comments from sources within the Egyptian investigation committee who said that the jet had shown no sign of technical problems before taking off from Paris.

He said the Airbus 320 was given a regular check by an Egyptian engineer and two Egyptian technicians at Paris airport.

"The engineer and the pilot both signed the Aircraft Technical Log which stated that the check found that all the plane's machines were safe," he said.

The investigation sources said the plane disappeared off radar screens less than a minute after entering Egyptian airspace and -- contrary to reports from Greece -- there was no sign that it had swerved sharply before crashing.

The crew did not make contact with Egyptian air traffic control, they said.

With no flight recorders to check and only fragmentary data from a handful of fault messages registering smoke in the plane in the minutes before it crashed, investigators are also looking to debris and body parts for clues.

One Egyptian forensics official said the small amount of human remains recovered pointed to an explosion on board though no trace of explosives had been detected.

But Hisham Abdelhamid, head of Egypt's forensics authority, said this assessment was "mere assumptions" and that it was too early to draw conclusions.