[Recovered debris of the EgyptAir jet that crashed in the Mediterranean Sea are seen in this still image taken from video]PARIS (Reuters) - Investigators have detected a signal from one of the black boxes of EgyptAir flight MS804 which plunged into the Mediterranean in an unexplained crash last month, France's aviation accident bureau said on Wednesday. "A signal from a flight recorder has been detected," a spokesperson for the BEA agency said, referring to the hunt for the missing aircraft in deep waters between the Greek island of Crete and the northern Egyptian coast. (Reporting by Chine Labbe; Editing by Richard Lough; Editing by Paul Taylor)