There was an earlier post...
With "....current underwater was in reverse direction as opposed to the surface, and they couldn't inform the boatman," then the search would be ahead of the divers drifting in the surface current since they surfaced up current far from the boat - perhaps too far from a SMB to be seen, and the crew looking the wrong direction.
"They drifted off and saw the search helicopters flying over their head twice without spotting them." How visible can a diver be from a plane? Even a SMB would be difficult to spot above. I carry a long list of signaling devices and with planes in mind this includes a signal mirror, 2 dive lights even on all day dives - one is a 2 day burn LED light, camera with strobe that can be fired independently from the camera, and a white kitchen trash bag that can float flat on the surface tied to me or maybe be inflated at night with a dive light shinning into it. I have not tested the last idea yet, but it's worth a try.