PARIS » French naval investigators using new, state-of-the-art software, believe they have narrowed down the location of at least one of the “;black box”; flight recorders of an Air France jet that crashed almost a year ago in the mid-Atlantic, French officials said Thursday.

The investigators used the software to re-analyze sonar recordings that were made in the weeks following the crash, when the box's “;pingers”; were still sending out signals, said Stephanie Prunier, a spokeswoman for the French Defense Ministry. Previous analyses of those recordings had failed to pick up those signals.

“;We don't know exactly where they are, but we have significantly narrowed the area”; to about 40 square miles, she said.

Air France Flight 447 went down in heavy thunderstorms on June 1 during a flight to Paris from Rio de Janeiro. All 228 on board were killed. Sea searches last year recovered more than 600 pieces of debris and 51 bodies from the ocean, but the black boxes and the bulk of the wreckage were not found.

Without the flight recorders, investigators have said it might never be possible to determine the cause of the disaster. So far, the main source of information about what happened has been a series of messages sent automatically from the plane to a maintenance base, which indicated there was a malfunction of the plane's airspeed sensors.

Speaking on French radio, Luc Chatel, a government spokesman, advised “;extreme caution”; about the news, saying that it remained uncertain whether the flight recorders could be retrieved from the rugged ocean floor, which at some points is almost three miles deep.

If the searchers succeed, he said, “;it would be obviously very good news for us, but particularly for the victims' families and for us all because we have been waiting for nearly a year to find out what really happened.”;

Defense Ministry officials informed France's transport minister, Dominique Bussereau, of the discovery on Wednesday night, Prunier said. Bussereau then contacted Jean-Paul Troadec, the head of France's air accident investigation bureau.

Martine del Bono, a spokeswoman for Troadec, said the bureau was studying the navy's analysis of the recordings in the hope of verifying their findings. “;As in every investigation, we remain cautious,”; she said. “;But we are crossing our fingers.”;

Once the location is confirmed, work can begin to try to retrieve them from the ocean floor. A Norwegian search boat equipped with three remote-controlled submarines has been at sea since Monday, part of a final effort to find the wreckage of the plane, an Airbus A330.

A previous three-week hunt of the 1,200-square-mile search zone ended last month without success.

The new software was provided by the French company, Thales, which was also the manufacturer of the doomed plane's airspeed sensors. The sensors malfunctioned in the minutes preceding the accident and investigators believe that their failure probably played a role in the crash.

So far, the French government, Air France and Airbus have spent nearly $40 million searching for the wreckage.