Egypt Air Flight 804: 'Black box' signals detected, French investigators say

Cairo (CNN)A French naval vessel has detected underwater signals from one of EgyptAir Flight 804's so-called black boxes, investigators said Wednesday.

Specialized locator equipment on board the French vessel La Place detected signals from the seabed in the Mediterranean Sea, the Egyptian investigative committee said in a statement.

The French Aircraft Investigation Committee later said it had confirmed the signals were from one of the aircraft's black boxes -- the flight data and cockpit voice recorders.

The Airbus A320, which had 66 people aboard, crashed in the Mediterranean on May 19 on a flight from Paris to Cairo. Since then, authorities have been searching for wreckage and the plane's data recorders, which could reveal evidence about what caused the crash.Authorities hope to locate the data recorders, so a specialized vessel managed by the Deep Ocean Search company can then retrieve them. That vessel is set to join the search team within a week, the investigative committee said.

So far, search teams have found small pieces of debris, victims' remains and personal effects from the plane. They haven't found the aircraft's fuselage.

This isn't the first time investigators have said they detected a signal from the plane.

Last week a lead investigator in the search said airplane manufacturer Airbus had detected signals from the plane's Emergency Locator Transmitter, a device that can manually or automatically activate at impact and will usually send a distress signal.

Time critical

The signals gave investigators a more specific location to detect pings from the black boxes, state media reported.

Time is of the essence: The batteries powering the flight recorders' locator beacons are certified to emit high-pitched signals for about 30 days after they get wet.

Once they're found, the black boxes will be brought to Egypt, a civil aviation ministry official told CNN. That's standard procedure, the official said, similar to what happened in November with the recorders from Metrojet Flight 9268, which crashed in Egypt's Sinai Peninsula.

The data recorders have been fixtures on commercial flights around the world for decades.

The flight data recorder gathers 25 hours of technical data from the airplane's sensors, recording several thousand distinct pieces of information. Among the details investigators could uncover: information about the plane's air speed, altitude, engine performance and wing positions.

The cockpit voice recorder captures sounds on the flight deck that can include conversations between pilots, warning alarms from the aircraft and background noise. By listening to the ambient sounds in a cockpit before a crash, experts can determine if a stall took place and the speed at which the plane was traveling.

But black boxes aren't perfect. In several cases -- such as the 1996 crash of TWA Flight 800 or the crash of American Airlines Flight 77 on September 11, 2001 -- authorities had hoped to find clues in the recorders, only to discover that the data inside had been damaged or the recordings had stopped suddenly.