It's not really a dipping sonar... it would just be a sensor assigned to the helo that is offset from the center of the platform by some assigned depth.
The game engine does not require an actual mast or cable for a sensor to be offset from a platform, this is the same way the dipping sonar works for the other AI helos (its just they follow doctrine commands exclusively and can be made to "lower" the sensor into the water) as well as sonobuoys.
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