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Originally Posted by Sleepdoc
Why would an active contact (known range and bearing at a moment in time) require a TMA solution
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Because it's precisely that: a snapshot of a moment in time. In order to extrapolate things like a target's course and speed, you need to gather and compare data from your sensors over a period of time. This is what TMA is for.
Since active sonar is only presenting you with a picture of the contact at one single moment (rather than OVER TIME as passive sonar would) your FFG friend will not be able to tell which way the contact is heading or how fast it's going. He can just say "oh, there's a contact 15 degrees to my starboard, five hundred yards away." In order to get the info you're looking for, he must make multiple active pings and compare the contact's location after each one.
I believe there is a known bug where an FFG's active sonar will not carry over the data to the TMA station. If you ping a contact in another platform a few times I think the TMA plot will automatically be updated with each bit of info obtained from the active station, but maybe I am wrong about that.