The logistics of recovering debris and remains from the Air France flight are complicated by its disappearance 930 miles (1,500 kilometers) off Brazil's mainland. Investigators should have an easier time recovering debris and clues in the crash of a Yemeni Airbus 310 with 153 people on board that went down Tuesday just nine miles (14.5 kilometers) north of the Indian Ocean island-nation of Comoros.

The black boxes emit an electronic tapping sound that can be heard up to 1.25 miles (two kilometers) away. While searchers for the Air France plane have detected some noise in the deep ocean, they have heard nothing from the flight recorders.

The Airbus A330 jet went down in the middle of the Atlantic shortly after midnight June 1. The crash date had been reported as May 31, as it was 11:14 p.m. on Brazil's mainland when the plane sent its last automated messages. But as searchers found debris and those messages were made public, it was clear the plane had crossed into a new time zone - and a new day - before it went into the ocean.

Without the crucial evidence the black boxes contain, investigators may never be able to determine definitively why the jet fell - despite the recovery of a substantial amount of wreckage and the remains of 51 people.

"The most you can do is a detailed forensic analysis of what affected the recovered items," Goelz said. "That may or may not give you a picture of what went on. But it isn't going to go to the cause of the accident, it will go to what happened after the event occurred."

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