PARIS - Air France Airbus jets experienced at least nine incidents in which airspeed probes iced over in the past year, according to an internal company report obtained by AFP Friday.

A probe into the June 1 crash of AF 447, in which an A330 jet flying from Rio to Paris plunged into the Atlantic with the loss of all 228 people on board, has focused on contradictory readings from its "pitot" speed probes.

French aviation investigators as well as the companies Airbus and Air France have each said there is no firm evidence so far linking speed monitors and the crash.

Nevertheless, Air France has upgraded all sensors on its long-haul fleet as a precaution after protests from pilots.

In an internal note sent to Air France pilots on Thursday, the company said it informed the planemaker Airbus and Thales, which makes the pitot probes, of eight incidents on A340 jets and one on an A330 over a year-long period.

An earlier report seen by AFP recorded five airspeed probe incidents last year, two of which caused triggered alerts.

According to the latest report, the first incident occurred in May 2008, involving temporary loss of speed data, followed by a second in July 2008 and three others in August 2008.

There then followed two operational incidents in September and October 2008, all on A340s.

Airbus and Thales were given a full briefing on the incidents, and asked to resolve the problem, according to the Airbus note.

"Numerous exchanges took place with the technical teams at Airbus," it said, noted that "no incident of this kind had been signalled previously."

Airbus replied to Air France, saying "the supposed origin of the incidents was icing over, due to the formation of crystals inside the airspeed probes," according to the report.

"Faced with our insistence on finding a solution, Thales and Airbus (will) carry out studies" on a new generation of probe, the Air France report says.

It said two further operating incidents were recorded at the end of 2009, one on an Airbus A340 and one on an A330.

"Airbus is contacted again several times" and "replies by confirming that it presumes the probes had iced over," Air France said.

According to the report, Airbus wrote to Air France on April 15, 2009, to inform it that tests carried out by Thales on new-generation probes showed a "much better response than the older model" to icy conditions.

In response, Air France asked Thales to accelerate the delivery of speed probes that were to be supplied from May 26, 2009, at a rate of a dozen a week.

French investigators probing the June 1 Air France crash have said that the airspeed sensors, or pitot probes, had been feeding inconsistent readings to the cockpit.

Conflicting airspeed data can cause the autopilot to shut down and in extreme cases the plane to stall or fly dangerously fast, possibly causing a high-altitude breakup.