A question ...
Can Sonar buoys hear the pinger?
Could a maritime patrol aircraft drop a pattern of sonar buoys to start localising the black boxes?
Yes, our Orion anti-sub aircraft are equipped with air-dropped sonobuoys with both passive and active sonar. The active equipment can map the ocean floor while passive buoys can detect underwater sounds including the ultrasonic pingers on DFDR's and CVR's.
Despite being on drug-interdiction duties, they would almost certainly had these buoys at the ready for deployment from their base of operations.