The flight disappeared nearly four hours after takeoff, killing all on board. It was Air France's deadliest plane crash and the world's worst commercial air accident since 2001.
The investigation is increasingly focused on whether external instruments may have iced over, confusing speed sensors and leading computers to set the plane's speed too fast or slow — a potentially deadly mistake in severe turbulence.
An Air France memo to its pilots Friday about the crash said the airline is replacing the Pitot tubes on all its medium- and long-haul Airbus jets.
Pitot tubes protrude from the wing or fuselage of a plane and help measure the speed and angle of the flight, along with less vital information like outside air temperature.
They feed airspeed sensors and are heated to prevent icing.
A blocked or malfunctioning Pitot tube could cause an airspeed sensor to work incorrectly and cause the computer controlling the plane to accelerate or decelerate in a potentially dangerous fashion.
On Thursday, European plane maker Airbus sent an advisory to all operators of the A330 reminding them of how to handle the plane in conditions similar to those experienced by Flight 447.
Peter Goelz, a former managing director of the National Transportation Safety Board, said that advisory and the Air France memo about replacing flight-speed instruments "certainly raises questions about whether the Pitot tubes, which are critical to the pilot's understanding of what's going on, were operating effectively."
But questions about speed sensors are only one of many factors investigators are considering. Automatic transmissions from the plane showed a chain of computer system failures that indicate the plane broke apart in midair.
President Barack Obama said at a news conference with French President Nicolas Sarkozy Saturday that the United States had authorized all of the U.S. government's resources to help investigate the crash.
Arslanian said investigators are searching a zone of several hundred square miles (square kilometers) for the debris.
An intensive international effort so far has failed to recover any confirmed wreckage, and concern has grown about whether searchers were even looking in the right place.
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, Arslanian said.
"We have no guarantee that the pinger is attached to the recorders," he said.