Narrative:

My first officer and I arrived at [the aircraft for an early morning departure]. Per company procedure I (captain) completed the cockpit preflight and the first officer completed the exterior preflight. The first officer reported no discrepancies. Just before departure; I conducted an abbreviated external inspection. I noted that all prop tie-down straps and pitot covers were removed. I also did not see an installed cowl inlet plug. Departure was normal; and we flew four legs with no abnormal engine indications. It was brought to our attention that in fact we had operated the airplane for four legs with the cowl plug sucked down into the intake and jammed on a splitter. A different crew operated the aircraft an additional leg with no problems before discovery.it has been determined that aircraft at our company of the same make/model/year have plugs that are worn; discolored; and ill-fitting. Although the plug could have been installed properly the night before; it appears it could have easily slipped down into the intake overnight; making it hard to detect. It is also possible the plug was simply pushed too far in by the previous crew making it difficult to see. A possible fix would be to incorporate a strap that connects the plug to the prop tie-down; to ensure a positive connection to something exterior to the intake. Also; in this incident; when the first officer noted that the plug was not installed he assumed that meant that the plug was simply missing from the aircraft and did not mention the missing part to me. Had he mentioned it; I would have taken a more close look into the intake in order to try to locate it.

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Original NASA ASRS Text

Title: PC12 flight crew reported they departed with an inlet cover still in the intake. Five legs were flown before the cover was noticed.

Narrative: My first officer and I arrived at [the aircraft for an early morning departure]. Per company procedure I (Captain) completed the cockpit preflight and the first officer completed the exterior preflight. The first officer reported no discrepancies. Just before departure; I conducted an abbreviated external inspection. I noted that all prop tie-down straps and pitot covers were removed. I also did not see an installed cowl inlet plug. Departure was normal; and we flew four legs with no abnormal engine indications. It was brought to our attention that in fact we had operated the airplane for four legs with the cowl plug sucked down into the intake and jammed on a splitter. A different crew operated the aircraft an additional leg with no problems before discovery.It has been determined that aircraft at our company of the same make/model/year have plugs that are worn; discolored; and ill-fitting. Although the plug could have been installed properly the night before; it appears it could have easily slipped down into the intake overnight; making it hard to detect. It is also possible the plug was simply pushed too far in by the previous crew making it difficult to see. A possible fix would be to incorporate a strap that connects the plug to the prop tie-down; to ensure a positive connection to something exterior to the intake. Also; in this incident; when the first officer noted that the plug was not installed he assumed that meant that the plug was simply missing from the aircraft and did not mention the missing part to me. Had he mentioned it; I would have taken a more close look into the intake in order to try to locate it.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.