Military planes and ships struggled through high seas and heavy winds Wednesday and found more debris from an Air France jet, while an investigator said the black boxes may never be found in the depths of the Atlantic.

Rescue vessels from several nations were sailing toward the site to start the recovery as aviation experts tried to determine why the plane carrying 228 people from Rio de Janeiro to Paris on Sunday night ended up in the sea.

A 23-foot (seven-meter) chunk of plane and a 12-mile-long (20-kilometer-long) oil slick were found early Wednesday, Brazilian air force spokesman Col. Jorge Amaral said. Rescuers have still found no signs of life.

The new debris was discovered about 90 kilometers (55 miles) south where searchers a day earlier found an airplane seat, a fuel slick, an orange lifevest and pieces of white debris.

The location of the new debris is consistent with where experts say currents in that part of the Atlantic would push anything on the surface.

The original debris was found roughly 400 miles (640 kilometers) northeast of the Fernando de Noronha islands off Brazil's northern coast.

The recovery effort is expected to be exceedingly challenging. Storm season is starting in the are and water depths sink down to 22,950 feet (7,000 meters).

Four boats and a tanker ship were en route to the scene but Brazil lacks equipment to scour the ocean floor, a Brazilian navy spokeswoman said Wednesday. Brazil was leading the search for wreckage, while France took charge of the crash investigation.