What was found
WHILE EN ROUTE FROM SIOUX FALLS, SD TO RAPID CITY, SD THE PILOT NOTICED THE HYDRAULIC PRESSURE WAS FLUCTUATING ON THE LEFT HAND ENGINE. SHORTLY THEREAFTER THE RIGHT HAND PRESSURE BEGAN TO FLUCTUATE. THE PILOT REQUESTED CLEARANCE TO RETURN TO SIOUX FALLS WHICH WAS GRANTED. EMERGENCY VEHICLES WERE DISPATCHED AS A PRECAUTION AND AN UNEVENTFUL LANDING WAS PERFORMED. INVESTIGATION REVEALED THAT A HYDRAULIC PRESSURE LINE HAD RUPTURED.