From BEA Report
with an additional ULB capable of transmitting on a frequency (for example between 8.5 kHz and 9.5 kHz)
I suspect that return traces using an echo sounder on 37.5kHz confirmed during the last two searches that temperature/salinity changes were creating inversion layers. This would greatly hinder the chances of a weak ULB signal on 37.5kHz getting to the surface from the depths associated with this search. The use of the lower frequency in the range mentioned will alleviate the problem.
A quick read of the BEA analysis of the ACARS messages which hadn't previously been explained, tend to demonstrate the ADIRU's had a major disagreement and the TCAS took a similar view and threw its hand in. Apparently no lightning was detected by satellites during the period of this upset.
mm43