Not to be a tw*at, but...
A pilot in a 206B who rolls the throttle off before takeoff to “check the freewheeling unit” is showing evidence of a poor or nonexistent aircraft checkout. That’s not how it’s done in turbines. The RFM does not require it. And depending on the particular 206, it may either tell you nothing or give you a false indication that your freewheeling unit is not working properly.
All helicopters with reciprocating engines have clutches of some sort. With the engine off the clutch is disengaged. Turning the rotor does nothing to the engine.
In a helicopter powered by a free-turbine engine such as the 206 there is no clutch. The freewheeling unit is all you have. Thus, with the engine off turning the rotor backwards turns the engine. If the engine does not turn when turning the rotor forward you have just proven that the FWU is working properly. Doing this when you take the MR tiedown off is the best way.
So move the rotor backward, and check that the turbine wheels are turning but not rubbing (or locked up). Turn the rotor forward again and make sure the FWU disengages and the engine does not turn. Pretty simple. Get in and go flying.
The thing we do at the end of the flight/day is called a “Decel Check” and has nothing to do with the freewheeling unit. It is merely a check of the scheduling of the Fuel Control Unit (FCU). And it’s weird because we do it from full throttle (100% N2) and count down to IDLE N1. The time cannot be less than X (I don’t remember the exact figure; at PHI I think we used two seconds). All engines were different; some came down to idle quickly - others took their sweet time. RR-Allison gave no *maximum* time for the decel.