Initial details of the handover of Air France flight AF447 from Brazil to Senegal have opened a rift between the two states, as investigators attempt to establish how long the Airbus A330 was out of contact before a formal emergency alert was declared.
Preliminary findings into the loss of AF447 indicate that, after the jet failed to respond to radio calls shortly before leaving Brazilian airspace, several hours elapsed while controllers in 10 different flight information regions tried to determine the aircraft's position.
Circumstances of the loss - close to the Brazil-Senegal oceanic airspace boundary where responsibility for the flight is handed over - have made the transfer issue a sensitive matter.
France's BEA investigation agency states that the flight "was not transferred" between Brazil's Atlantico and Senegal's Dakar oceanic centres. This has been backed by West African air navigation service ASECNA.
But the Brazilian air force says it wants to "eliminate doubts" about the procedures that were followed.
It has publicly issued an audio segment of the moment the Atlantico controller co-ordinated transfer of AF447 to Dakar, when the A330 was estimating reaching the Brazil-Senegal airspace boundary - the waypoint designated TASIL - at 02:20 UTC.
Only changes in excess of 3min to this estimated time would have required further co-ordination with Dakar. But the estimate was never revised because the Atlantico controller could not raise AF447 after the last radio contact at 01:35UTC.
As a result, argues the air force, Dakar "theoretically" assumed control of the aircraft at 02:20UTC.
But in a statement ASECNA claims the "onus" was on the Atlantico controller to call his counterpart at Dakar centre to confirm the aircraft's arrival at the airspace boundary. "This formality was not performed," it says, and the aircraft did not contact Dakar to "signal its presence".
ASECNA rejects as "totally unfounded" the Brazilian suggestion that aircraft can be assumed to have entered Dakar airspace if the Dakar centre does not warn otherwise.