French investigators are unlikely to establish the exact cause of a fatal Atlantic plane crash in a report this week but may recommend ways to help locate black boxes more easily, sources familiar with the incident said.
France's BEA accident investigation authority is due on Thursday to issue its final report into the Air France crash in which 228 people died.
Flight AF 447 from Rio de Janeiro to Paris crashed into the Atlantic on June 1 after flying into stormy weather.
The 'black box' flight recorders remain missing and only small parts of the wreckage have been found of the Airbus A330.
"I don't expect much new concrete information on the cause of the crash," a source familiar with the investigation said.
A second source familiar with the incident concurred, saying the report would add little to an inconclusive preliminary report issued in July.
The new report's conclusions are currently being finalised, the sources added.
The BEA declined to comment.
The July report identified problems in handing responsibility for the aircraft between controllers but said it was too early to say what caused the plane to hit the ocean.
Speculation has focused on possible icing of the aircraft's speed sensors, which appeared to give inconsistent readings and may have disrupted other systems.
Safety authorities ordered checks on the sensors known as 'pitot probes' and restricted the use of the type installed on the plane, made by France's Thales.
But investigators are not expected to pin the blame on any one issue, one source close to the investigation said.
Instead, the BEA is expected to make at least three recommendations on general aircraft safety, this source said.
These include extending the life of locator beacons attached to the flight recorders to 90 days from 30 days.
Regulators could also be asked to consider ordering further beacons to be attached to important parts of the aircraft structure to assist in locating wreckage in the event of a crash. Such beacons would need to be active for 30 days.
Plane makers may also be asked to study the feasibility of installing monitoring systems that send information on basic parameters such as position, course and altitude back to an airline's maintenance base even when operations are normal.
The few clues available on the cause of the crash include fragments of error messages sent out by the aircraft.
The crash fuelled a debate in the aviation industry over whether more data should be streamed via satellite but the cost of communications has so far been deemed prohibitive.
Some safety officials are meanwhile calling for scientific research to be carried out into weather conditions at high altitudes in turbulent zones such as the equator.