Air France is now scrambling to replace potentially faulty speed sensors on its Airbus A330s and A340s but this does not mean the risk of a similar disaster to the loss of Flight 447 has been averted.

Neither the airline nor the investigation team know whether the sensors, known as pitot tubes, played any part in the crash. In the absence of any hard information - and under pressure from pilot unions - Air France is acting on speculation. It is responding to the theory that there may be a link between previously-detected problems with the tubes and a series of error messages sent by the doomed airliner in its final minutes.

The pilots of Flight 447 received conflicting speed readings, possibly caused by ice blocking one or more of the three pitot tubes. The autopilot on an Air France Airbus cut out last year following pitot tube problems and the autopilot on Flight 447 also either failed or was switched off by the pilots.

However, problems with speed readings, even if they do turn out to have been involved, are very unlikely to be the only cause of the crash. The pilots could have used other instruments to fly the plane safely out of the storm.

Times Archive 1962: Crash pilot's protest before flight

The two major crashes of Air France airliners last month have aroused deeper than usual anxieties in France

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Almost all crashes of modern airliners are caused by a previously-unknown combination of very usual circumstances. Highly-trained pilots only tend to be caught out when they are trying to cope with two or more problems at the same time.

Passengers taking future flights on A330s should take little comfort from knowing that pitot tubes have been replaced or were of a different type.

Qantas unhelpfully tried to suggest yesterday that it had nothing to learn, or fear, from the Air France crash because its pitot tubes were made by a different manufacturer.

The lessons from the crash are likely to lie in the complex relationship between pilot and computer in the modern cockpit. Computers have made flying much safer because planes are less vulnerable to simple pilot error. But when the computer fails in a highly automated cockpit, it can be much harder for the pilot to regain control.

The best news for nervous flyers is that the discovery of the tail fin of Flight 447 raises the chances of finding the black boxes, which were located just under the fin. The boxes are placed there to give them the best chance of surviving reasonably intact if the aircraft nosedives.

Only the painstaking process of deciphering the flight data and voice recorders can ensure that whatever caused 228 deaths last week is never allowed to happen again.

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