"there are no daily maximum limits on flight time."
If you do a 15 hour day, you can't fly more than 8 hours, and the 42 days can be extended to 60 or more on a fire (though you must have 5 days off before and after any period of 27 days on duty). "6 non-overlapping periods of 30 days" means more or less 6 months straight.
Dunno why the DHC-6 - maybe they really mean bush flying, but loads of other planes are used for that. heli-logging has its own special deals, rather like pleasure flying does in UK.
It says a lot for the pilots that there aren't more fatigue-related accidents.
Phil