PARIS (Reuters) - A second ship with specialist search equipment will join the hunt for the "black box" flight recorders and wreckage of a crashed EgyptAir jet on Friday, the head of France's air accident investigation safety agency said on Thursday.

A French naval supply vessel picked up a signal from one of the two recorders on June 1, andEgypt has chartered a second vessel operated by Mauritius-based Deep Ocean Search, equipped with a suitable sonar and an underwater vehicle.

Remi Jouty, director of the BEA air accident agency which is advising Egypt on the underwater search, said the first ship continued to pick up locator signals from the first recorder, whose location had been narrowed to a radius of 1-2 kilometres.

Pending the search for the two flight recorders, one for cockpit voice recorders and one for data, the Egyptian-led probe is still "very far" from understanding why Flight 804 crashed into the Mediterranean on May 19, killing all 66 people on board, Jouty told a group of aviation journalists in Paris.

(Reporting by Tim Hepher; Editing by James Regan)