Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 250; Flight Crew Total 17500; Flight Crew Type 650
Training / Qualification; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Inflight Shutdown; Flight Crew Landed As Precaution
Aircraft; Human Factors
While climbing to cruise altitude of FL230 we noticed fluctuations of 50 to 100 lbs of torque on the right engine. While looking for a cause and leveling at our cruise altitude we observed the oil pressure of the right engine dropping down below 20 psi. We contacted ATC requested a turn back towards our departure airport while we trouble shooted the problem. During the initial climb and enroute climb the engine instruments were scanned and all parameters were correct; in limits; and matching. After a short check of the engine and the oil pressure dropping more; it was determined that a precautionary shutdown was required to prevent any damage to the engine.We then decided that a landing was required since only one engine was operating. A safe landing was accomplished without any further issues.Maintenance personnel checked out the aircraft [and] it was determined that the right engine dipstick was not properly locked in place and sometime in the final segment of the climb to cruise the dipstick came loose. Oil then leaked out of the engine causing the low oil pressure. The engine was then serviced per the Beechcraft Maintenance Manual and returned to service.The takeaway from this event is to have everyone double check what has been done or check with any engine before closing and locking the cowling.
BE9L instructor pilot reported torque fluctuations and low oil pressure in right engine; so the engine was shut down and a precautionary landing accomplished. On the ground it was determined the oil dipstick was not locked properly before flight.