[Pisces]

1) Ehm, radar perhaps!?! It isn't passive, but it is detection and tracking. Another option would be a periscope search. I don't think you can make a solution based on bearings alone against a plane or helo. Your speed is simply too low compared to theirs to make it a meaningfull solution. Iirc LWAMI did alter sonar sensors and noise emmissions (height/depth limits) to make airborne targets detectable. So you still might detect them if they are really near.

2) As soon as a TIW report comes I would start searching for anything in my vicinity that is loud. If that noise drifts quickly then you can be relatively sure it is not pointed at you. But if the direction doesn't drift then you should expect to be acquired and run and mask yourself.