Date: 201207
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: PA-31 Navajo/Chieftan/Mojave/T1040
Operator: Air Carrier
Operating under: Part 135
Flight plan: VFR
Mission: Passenger
Flight phase: Initial Climb
Airspace: Class E ZZZ
ATC / advisory: CTAF ZZZ
Aircraft component: Oil Filler Cap
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Workload; Situational Awareness; Time Pressure
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Maintenance Action; General Release Refused / Aircraft Not Accepted
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Pre-flighted aircraft including check of left and right engine oil quantity. Dip sticks returned to normal 'snapped' locked position. Started aircraft and taxied away from terminal and preformed normal 1st flight runup and checks. Returned to terminal and shut down (approximately 10 minute run time). No anomalies noted on shutdown. Loaded 7 passengers for scheduled departure departed Runway XX. On climbout at approximately 1;000 FT MSL [we] advised by passenger that oil was streaming from right engine cowling filler door. Oil stream confirmed engine operation and gauges all normal. [We] advised CTAF that returning to the departure airport for landing due to right engine oil leak. Maneuvered to rejoin 3 NM final Runway YY [we] executed normal F-40 landing; exited runway and taxied to terminal south gate with cabin door in closest proximity to gate. [We were] met at gate by Manager and maintenance vehicle and personnel. Smoke noted on shut down from right engine cowling. Exited aircraft and opened main cabin door. [We] expedited all passengers from aircraft to terminal due to potential fire hazard. Requested Airport Manager and maintenance vehicle continue to stand by at aircraft until smoke had subsided. Inspected right engine through cowling doors; found right engine oil dip stick had popped up. Oil visible inside/outside cowling and under wing; no fire detected. Dispatch and Company Maintenance contacted by phone; passengers moved to other C208 (holding at gate). Aircraft grounded in flight log. This aircraft is outfitted with 'snap down' style oil dip sticks. These dip sticks were returned to the normal stowed snapped down position on preflight. I believe had that not been the case; there would have been evidence of oil leak and smoking from the :10 minute engine run that preceded this flight. Therefore; it appears that this dipstick failed during initial flight. This is the 2nd known instance of loose dipstick and oil leak that resulted in an interruption of flight on this aircraft. I feel that these filler necks and dipsticks should be modified with the 'screw-in' type to prevent future failures.




Synopsis: A PA31 pilot returned to land because a 'snap down' oil dip stick lock opened after takeoff allowing a passenger to detect the streaming oil.