The factual elements relating to the history of the flight that the investigation depends on are at present still limited to the maintenance and position messages transmitted by the ACARS system.
Finding the wreckage and reading out the flight recorders remain the key to any possible understanding of the circumstances and causes of the accident and thus to any safety lessons that may be drawn to prevent any recurrence.
The BEA has, nevertheless, already been able to issue several safety recommendations concerning the certification of Pitot tubes, finding wreckage, as well as on recovering flight data. These recommendations have accelerated the work undertaken in these fields.
The maintenance messages transmitted in the last few moments of the flight brought to light a loss of speed information, very likely linked to a phenomenon of blocking of the Pitot tubes by ice crystals. This blocking led to the loss of some automated systems. It appeared, however, that airplane certification standards did not cover all of the conditions that could be encountered in clouds at high altitude. The BEA made a recommendation aimed at better defining these conditions and consequently reviewing the certification criteria, in particular those of Pitot tubes. The European Aviation Safety Agency (EASA) took this recommendation into account and is undertaking the corresponding research.
Another series of recommendations made by the BEA is intended to ensure rapid localisation of the wreckage of an aircraft involved in an accident over the high seas.
Flight AF 447 was transmitting its position automatically every 10 minutes, which corresponds to about 80 nautical miles (148 km). The BEA recommendation aimed to ensure regular transmission of the basic parameters (position, altitude, speed, heading). ICAO is currently studying the necessary means (regular transmission of data, triggered transmission, deployable recorders) that would allow the wreckage to be localised within a radius of 4 nautical miles (7 km).
In order to facilitate detection of wreckage, whatever the depth may be, the airplane's recorders are equipped with beacons that transmit a characteristic signal for a certified period of 30 days. Their main weakness is their limited operating time. The recommendations made by the BEA in its second interim report on the accident to flight AF 447 led ICAO to prepare a regulation that would extend to 90 days the transmission time for beacons. ICAO also adopted another BEA recommendation aimed at adding another beacon to the airplane, transmitting on a lower frequency from the others and consequently having greater range.
In the future, a sample of the data contained on the flight recorders could be transmitted automatically in circumstances that could lead to an accident. Nevertheless, this possibility is no substitute for localising the wreckage, since investigations will always need access to all the data as well as to an examination of the wreckage.
