Air taxi helicopter pilot reported a fuel cap was discovered missing during preflight.

Attributes
ACN	1582774
Time
Date	201810
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	MBB-BK 117 All Series
Operating Under FAR Part	Part 135
Flight Phase	Parked
Component
Aircraft Component	Fuel Tank Cap
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Commercial
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy

Narrative:

During post flight/refueling discovered the fuel cap was missing behind secured fuel door. After further investigation the aircraft was flown the night before to another airport/FBO where the fuel cap was not reinstalled after refueling. Fuel cap was recovered by airport personnel. Fuel sample was taken after post flight.always verify the fuel cap and door are secured after refueling. Also follow all items on the aircraft preflight checklist.

Original NASA ASRS Text

Title: Air taxi helicopter pilot reported a fuel cap was discovered missing during preflight.

Narrative: During post flight/refueling discovered the fuel cap was missing behind secured fuel door. After further investigation the aircraft was flown the night before to another airport/FBO where the fuel cap was not reinstalled after refueling. Fuel cap was recovered by Airport personnel. Fuel sample was taken after post flight.Always verify the fuel cap and door are secured after refueling. Also follow all items on the aircraft preflight checklist.

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.