Date: 202111
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Caravan 208B
Operator: Air Carrier
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Single Pilot; Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Workload; Communication Breakdown; Time Pressure; Physiological - Other; Fatigue
Second reporter function: First Officer; Pilot Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural FAR; Flight Deck / Cabin / Aircraft Event Other / Unknown
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate
Result: General Maintenance Action
Contributing factors: Company Policy; Human Factors
Primary problem: Human Factors

Narrative: On post flight inspection in ZZZ Captain noticed an oil seepage on the left side of engine cowling. Discovered that the oil Dip Stick was missing. Reported same to Maintenance Control; Chief Pilot; Chief Training Captain; and Director of Operations. New stick was installed and oil added. One (1) quart brought engine to Full Cold mark. Maintenance ran engine and released aircraft back into service. Completed the next four (4) flights without any issues. Day before; Date1; 3 leg Deadhead; XA:35 to XK:45 ; 9 1/2 hours on duty. DH (Deadhead) was moved up Date2 by 6 hours. During DH I was informed that my Copilot would not be arriving until XR:30 and I was expected to pick him up at ZZZ1 airport. Scheduled to report Date3 at XX:55. I informed Operations that would not be adequate rest for either of us. Copilot was told to stop in ZZZ and join me the next morning on my arrival there. I filed flight plans accordingly. That evening I was rescheduled again; adding 2 more flights and reporting at XX:15 . Reposition part 91; No Autopilot; from ZZZ1 to ZZZ2. Pick up new Copilot and fly passengers to ZZZ then change copilots and fly ZZZ; ZZZ3; ZZZ; ZZZ2; ZZZ1. arriving at YM:30; 15.5 hours duty. During preflight I missed the missing Dip Stick. Dark; tired; cold; plane just released by Maintenance for service; running late. Dip stick was later found in hangar where 2 Mechanics left it the night before. Why they removed it to hangar I do not know.I was told to fly the remainder of my day when incident occurred with Management's full knowledge that it was my mistake during preflight to catch missing dip stick. They also had me to fly with minimum rest the next day 4 passenger flights; and then 3 DH flights home to ZZZ4. I was informed during my DH that I was being investigated and to remain home until called back to work. I [reported] company Incident/Debrief within 24 hours of being asked to. Company routinely reschedules pilots into situations where they are late; little sleep; no food. Pushed to fly single pilot many times.


Second narrative: I was SIC (Second In Command) during the relevant day. The day began with the PIC (Pilot In Command) flying single-pilot from ZZZ1 to ZZZ2. At ZZZ2 I joined the active crew (PIC) for one leg on the same aircraft - flying ZZZ2 to ZZZ: I waited inside the terminal at ZZZ2 for the plane to arrive from ZZZ1. After the plane landed I met the PIC inside the terminal; and heard him say 'we just need fuel' to the Gate Agent. Upon hearing this I took my belongings from the office; exited the terminal to the plane to supervise fueling. The PIC did not instruct me to perform any checks on the plane. After fueling completed I performed a 'walk-around' of the plane to check externally. I took the fuel sump to check the fuel; poured it out and returned the fuel sump to the pod. Per company FOM pre-flight checks are delegated by Captain to FO (First Officer); this was my first time joining an active crew from another base mid-day; and pre-flight was not discussed. As part of pre-flight checks; oil level is typically checked in the first flight of the day (or when switching aircraft) - since I was joining an active crew that had already completed the first flight of the day on this plane I did not proactively check oil.After fueling completed I entered the terminal; saw the PIC at the entrance; told him I was going to wash my hands. After washing my hands I signed the manifest and we exited the terminal to the plane. We boarded the plane and flew to ZZZ. During the post-flight inspection in ZZZ we saw oil on the side of the aircraft coming from the engine; opened the cowling and discovered the dipstick missing. Later on it was discovered that the dipstick was left where the plane originated in ZZZ1 by the Mechanic who added oil to the engine the evening prior and apparently did not return it.The missing dipstick was not discovered by the PIC in pre- or post-flight of the first leg prior to me joining; and I did not discover the dipstick missing before I joined the subsequent leg of flight. No issues occurred in flight (no lights turned on/no engine issues) and to my understanding the engine was not damaged.While many human factors contributed to this chain of events; it is my personal responsibility to proactively ensure a safe and airworthy aircraft regardless of whether PIC instructed me to perform certain checks or not. Additionally; I believe there is a lack of clarity in company procedure for pilot joining an active crew (what checks need to be performed). In my prior experience flying I checked oil (and performed all other exhaustive pre-flight checks) on the first leg of every day and on the first leg of a new aircraft. In this situation the plane was on the ground for [about] 15 minutes including fueling and boarding of passenger and when the PIC said 'we only need fuel' I did not challenge him and question whether he performed pre- and post-flight checks prior to me joining. On a personal level; in the future I will be proactive regarding any aircraft I fly in; questioning the PIC and will not assume the pilot flying with me has completed any checks; regardless of seniority. On a company procedures level; I think clarity regarding required checks for crews that partially change throughout the day (whether regarded as new crew/day or same crew/flight day) will be helpful. Generally; communication between crew members is key to prevent assumptions and minimize human error.I cannot speak to the human factors from which the issue originated - what caused the Mechanic to forget to replace the dipstick or what occurred during the pre-flight checks of the PIC in ZZZ1.


Synopsis: C208 Flight Crew reported engine oil dipstick missing during post flight inspection.