Date: 202107
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: Haze / Smoke; 10
Light: Daylight
Aircraft: PA-44 Seminole/Turbo Seminole
Operator: Corporate
Operating under: Part 91
Flight plan: VFR
Mission: Training
Flight phase: Cruise
Airspace: Class E ZZZ; Class G ZZZ
ATC / advisory: CTAF ZZZ
Aircraft component: Oil Storage
Component problem: Improperly Operated
Reporter organization: Corporate
Reporter function: Pilot Flying; Instructor
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Commercial
Human factors: Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Aircraft Aircraft Damaged; Flight Crew Inflight Shutdown; Flight Crew Returned To Departure Airport; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Aircraft; Procedure
Primary problem: Procedure

Narrative: During the preflight of the aircraft; my student performed the inspection. He called me in when he was having trouble removing the oil dipstick of the right engine to inspect oil level since it was secured very tight and was hot to the touch. I came out there with a napkin to use as an insulator for our fingers and managed to loosen the dipstick by using both my hands. I checked the oil level and handed the dipstick to the student for him to do the same. He placed the dipstick back in and secured it; and I doubled checked that the stick was secure by loosening and retightening it. I then proceeded to run my own quick check of the aircraft by verifying the oil in the left engine and checking the fuel quantity onboard. We found no issues with the aircraft and proceeded with the flight.About an hour into the flight; we were in the south practice area performing Vmc demo with the student at the controls. During the maneuver; I had noticed an oil slick starting to form off the right engine. For the maneuver; we were operating the right engine at full power while the left was idle. To make sure we are all on the same page; I pointed out the slick and had him start turning back to ZZZ. I instructed him to scissor the throttles; go full power on the left engine and idle the right engine. I immediately called up our dispatch and informed them of our engine trouble while they coordinated preparations at the school; airport; and rescue services as part of the company procedures. About three minutes after we idled the right engine; the oil temperature was rising to the limit. Since we were holding 3;000 feet at the time with an idling engine with good performance; and I did not want to risk having a seized engine I elected to shut the engine down and feather it. We informed dispatch; and then followed the appropriate checklist. And elected to continue to ZZZ since they still needed time to prepare the field for our arrival with emergency services; familiarity; and long runways available. On the way back; I shifted my attention to the student and briefed what happened; and what we are going to do from now. During this time; I had him at the controls flying while I ran the checklists with him. I briefed that I would have him fly to ZZZ but once we start maneuvering; I will take the controls for descent and landing. As we were nearing the field; dispatch called us requesting we circle the field if performance allows for a few minutes while they still waited for rescue to arrive. Once we were about 3 miles south at 3;000 [feet]; dispatch called again telling we do not need to circle anymore; and that the airport will not call rescue. I really did not want to stay in the air longer than we needed to; and changing the plan now would have increased risks; I opted to continue to land. I took the controls at this point; and since we needed to lose altitude; I decided to fly a normal pattern and flew down to make a normal 45 entry for runway 20. Runway 20 was the longest runway with most favorable wind conditions. The landing was successful. The airport was closed for our recovery; and we planned to shut down on the runway and get a tow; but I was nervous about another aircraft behind me on short final; so I used the remaining speed of the aircraft to turn off onto the taxiway at about 10 knots.During the post flight inspection; we could not see anything out of place other than the oil streaks. We checked the dipstick and saw that it had slightly loosen but appear to be seated. But when maintenance performed their inspection; they determined the oil dipstick was cross threaded. They determined this was the most likely source of the oil leak. Only about a quart of oil was lost in flight.I think obviously the biggest factor here was the dipstick not secured properly. I was not aware how easily the dipstick could be cross threaded. The biggest learning moment for me was paying closer attention to how the dipstick is seated. In the specific aircraft; the dipstick sits directly on the engine block; and you can only easily see the dipstick from a top view unlike other aircraft I operate such as the other [aircraft type] where the dipstick is sits on a pipe that protrudes from the engine where the dipsticks cap is visible from the side. I think what also did not help was the fact we used a napkin to hold the dipstick during the preflight; which also visibly covered it. I think from here on out I am going to make sure some gloves are accessible and emphasize to my students the potential risk of cross threading.However; I am concerned about the airports handling of this situation. It was revealed when we landed; the airport management seemed to have not deemed our situation important enough to call in fire rescue as a precaution. They also have seemed to do a poor job of closing the airport as aircraft were still taking off and landing even when they announced multiple times over the radio the airport is closed. When I landed; a aircraft was flying not too far behind us in the pattern; and I had to move the aircraft on a single engine off the runway out of concern they would land on top of us which added the risk to us. But in the end of the day; the aircraft made it back in one piece; and most importantly my student and I made back safe.




Synopsis: PA-44 instructor pilot reported a cross threaded oil dip stick caused a loss of oil inflight; leading to an inflight shut down and air turn back.