Air France has asked for an outside panel of experts to review its security procedures, as investigators continue to look for an explanation behind the June crash of one of its jets in the Atlantic Ocean that killed all 228 people aboard.

The airline informed its pilots of the planned security review in writing, company spokeswoman Veronique Brachet said Thursday. The panel will be made up of an as-yet undetermined number of independent air transport safety experts "who will look at all aspects of our operations as concerns safety," Brachet said.

The makeup of the panel will be known in the coming weeks and it will include both French and non-French members, Brachet said.

In the letter to the pilots, a copy of which was obtained by The Associated Press, Air France says "the absence of clearly established factors for this accident means we cannot say with certainty that the measures taken since respond to the problems posed."

Air France will use the panel's findings "as the basis for our process of continually improving safety," according to the letter.

The plane was flying from Rio de Janeiro back to the French capital when it went down in a remote area of the Atlantic, 1,500 kilometers (930 miles) off Brazil's mainland and far from radar coverage. Automatic messages transmitted by the plane show its computer systems no longer knew its speed, and the automatic pilot and thrust functions were turned off.

Experts have suggested that sensors, called Pitot tubes, may have iced over and sent false speed information to the computers as the plane ran into a thunderstorm at about 35,000 feet (10,600 meters).

Air France is now starting a training program for pilots on how to manage a Pitot malfunction at high altitudes of the type possibly experienced on Flight 447.

Previously, Air France had only offered simulator training for Pitot malfunction on take-off and landing.