DAKAR, Senegal (CBS) French Airborne Warning and Control System (AWACS) plane has been flying missions with two other French military planes over the Atlantic from a French airbase in Senegal, but French officials said they had not found debris of Air France Flight 447.
A pilot said they still have no firm idea of where the plane came down and minute searches of vast areas of the Atlantic could take some time.
French Air Force Lieutenant Colonel Vincent Chincho Dabadie said a single flight could perhaps search an area of 300 miles by 100 miles but officials in Brazil say the Atlantic weather is currently severely hampering the search for debris from the plane.
One senior Brazilian naval officer said on Friday that none of the wreckage found so far could be confirmed as from Flight 447.
Investigators trying to establish the cause of the world's worst aviation disaster since 2001 are looking at the possibility that speed sensors, or an external instrument key to collecting speed data, failed in unusual weather, two aviation industry officials said on Thursday.
The "black box" cockpit recorders, built to give off signals for around 30 days, even underwater, could be miles below the surface of the Atlantic Ocean.
Brazil lacks the equipment needed to reach the ocean floor, a Brazilian navy spokeswoman said, so if the black boxes are at the bottom of the sea, recovery will have to wait for the arrival early next week of a French research ship with remotely controlled submersibles that can explore down to 19,600 feet (6,000 metres).
If they can't be recovered, investigators will have to focus on maintenance records and a burst of messages sent by the plane just before it disappeared.