auv-ee:
Thank you for pointing me to your previous very interesting post on the subject.
Can we assume that a 20db signal to noise ratio is about the detection capability of TPLs ?
Since we are in the ITCZ intermittent heavy showers have a significant probability of occurring at any time. I read in a US Navy paper that rain drops impacting sea surface and implosion of air bubbles caused by rain produce noise in the 1-100 kHz band with max SL @ 20 kHz and SL can be up to 30 dB above sea surface noise though I think the intensity is lower at great depths. It seems that if the TPLs were flown at, say 1700 m from the nearest pinger a simple shower occurring at the same time would have prevented detection. As I understand phase I, any area was swept only once so perhaps the failure was only bad luck.
OTOH, it is very possible that both ULB failed in the crash.