Probers: Flight 447's Autopilot Was Off

Signals sent by Air France Flight 447 before it disappeared show its autopilot wasn't on, the head of the French agency leading the probe into the crash of 447 said Saturday.

Agency head Paul-Louis Arslanian said it was not clear if the autopilot had been switched off by the pilots or had stopped working because it received conflicting airspeed readings.

Plane manufacturer Airbus says the probe found the flight received inconsistent readings from different instruments as it struggled in a massive thunderstorm.

Alain Bouillard, head of the investigation into the crash, told reporters that, "we also saw messages that show the automatic pilot wasn't working."

An Air France memo to its pilots Friday about the crash of Flight 447 said the airline is replacing instruments that help measure airspeed on all its medium- and long-haul Airbus jets.

Investigators have focused on incorrect speed readings as one potential factor in the crash.

Arslanian said investigators are analyzing 24 messages sent automatically by the plane during the last minutes of the flight.

He said investigators are searching a zone of several hundred square miles for the debris.

It is vital to locate a beacon called a "pinger" that should be attached to the cockpit voice and data recorders, now presumed to be deep in the Atlantic, he said.

"We have no guarantee that the pinger is attached to the recorders," Arslanian said.

Holding up a pinger in the palm of his hand, he said: "This is what we are looking for in the middle of the Atlantic Ocean."

Investigators are trying to determine the location of the debris in the ocean based on the height and speed of the plane at the time the last message was received. Currents could also have scattered debris far along the ocean floor, he said.

"You see the complexity of the problem," he said.

Laurent Kerleguer, an engineer specialized in the ocean floor working with the investigation team, said the zone seen as the most likely site of the debris was 15,112 feet at its deepest point and 2,835 feet at its shallowest.

Water salinity and temperature can affect the distance that the beacon's signal can travel, Kerleguer said.

The Airbus A330 from Rio de Janeiro to Paris disappeared nearly four hours after takeoff on Sunday night, killing all 228 aboard. It was Air France's deadliest plane crash and the world's worst commercial air accident since 2001.