Originally Posted by
Auxtank
These days are not like the old days - FDR/CVR is written to solid state memory modules and doesn't necessarily need to be 'transitioned' from retrieval depth to surface depth.
The reason for keeping recorders in clean fresh water when recovered from salt water, is that if the case or seals have been damaged and salt water reaches any of the electrical contacts, they will start to rapidly corrode once exposed to the oxygen in the air.
Keeping the whole unit in fresh water delays that corrosion until it can be disassembled in a clean, controlled environment.