Air France Black Box Search Passes 30 Days

French investigators say the search for the black boxes of Flight 447 is continuing although they are no longer certain to emit signals.

The flight's voice and data recorders are guaranteed to emit signals for 30 days after an accident. Tuesday marks 30 days since Air France Airbus A330 plunged into the Atlantic. All 228 people aboard were killed.

However, sources at Honeywell (which manufactures the black boxes for A330s) and Dukane Corp. (which manufactures the underwater locator beacons or "pingers" in the boxes) who are familiar with aspects of the investigation concerning the search for the black boxes tell CBS News that the specific type of boxes that were on Flight 447 will continue to emit a signal after the 30-day mark.

They add that the signal will be consistent and at full-strength (approximately 160 decibels) until the end of the battery life when the signal "will drop off fairly rapidly ... and then it just stops."

They tell CBS News that will occur "in a few days... maybe as much as a week" from now. After that, no signal will be emitted.

"It does not continue operating with decreasing signal strength," the source said.

Martine del Bono, spokeswoman for the French air accident investigation agency, says it "is continuing the search" as long as there is a "reasonable" chance of locating the black boxes.

She gave no final deadline Tuesday for ending the search.

The black boxes could be key to determining what happened to the plane.

Brazil has ended the search for more bodies.