French investigators have clarified that no signals have yet been identified from the flight recorders on board the crashed Air France Airbus A330.
Resources mobilised since the aircraft was lost on 1 June have so far failed to detect any trace of the recorders' location beacons, despite earlier claims in the French press that signals had been picked up.
"No signals transmitted by the flight recorders' locator beacons have been validated up to now," says the French investigation agency Bureau d'Enquetes et d'Analyses.
"In the context of the sea searches that are under way, work is undertaken on a regular basis that is aimed at eliminating any doubts related to any sounds that may be heard."
The recorders transmit a 10ms sonic pulse at a frequency of 37.5kHz, at intervals of about 1.1s, at 160dB. The devices are designed to continue transmitting for at least 30 days.
Several vessels, including a nuclear submarine, have been using electronic deep-water scanning equipment in a bid to detect these signals. The ocean in the search area reaches a depth in excess of 4,600m (15,100ft).
Brazil's defence ministry adds that, since the loss of the A330, search aircraft have clocked up 1,350hr in an operation covering 320,000km².