Narrative:

I checked weather before departing sending facility. Weather at sending facility was OVC033 and 10SM. Weather at closest reporting station along route was FEW026 BKN041 and 10SM. I also checked the helicopter emergency medical services (hems) tool and it showed VFR weather conditions with some rain showers along the route. About 10 min from receiving hospital I encountered light to moderate rain showers and visibility between 6 and 7 NM. Because of the rain it was difficult to estimate the ceiling; but I thought I was more than 500 feet below the clouds. About 7NM west of [the hospital] I encountered inadvertent IMC (iimc). It happened extremely fast. I immediately transitioned to instruments. Once the aircraft was stable I initiated a turn to return to VMC. I maintained my cruising altitude as I turned. The company iimc procedure calls for a climb to the MSA. The OAT indicated 3.5C and I did not want to risk climbing into icing conditions. I knew that my cruising altitude would keep me clear of all terrain and obstacles in the area; and I knew that there were VFR conditions behind me and to the north. Approximately 1-2 min later I returned to VMC.I marked the 'reduced safety standards' box above because I did not maintain the safety standard of cloud clearance and visibility for the class of airspace I was in.I was wearing night vision goggles (nvgs) for the flight. It can be difficult to detect the extent of reduced visibility conditions while using nvgs. In the future I will periodically look under my goggles to help identify reduced visibility conditions in front of me. If I can identify the conditions sooner than I can deviate prior to entering the IMC. One final note. The altitude and heading reference system (ahrs) 1 and the auto pilot were MEL'd for this flight. This increased my workload. In the future; when items that increase my workload are MEL'd I will increase my personal limitations for ceiling and visibility.

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Original NASA ASRS Text

Title: Helicopter Captain reported encountering IMC conditions during a night VFR ambulance flight. Pilot reported a turn to return to VMC and mentioned that wearing Night Vision Goggles can make it difficult to detect reduced visibility conditions.

Narrative: I checked weather before departing sending facility. Weather at sending facility was OVC033 and 10SM. Weather at closest reporting station along route was FEW026 BKN041 and 10SM. I also checked the Helicopter Emergency Medical Services (HEMS) Tool and it showed VFR weather conditions with some rain showers along the route. About 10 min from receiving hospital I encountered light to moderate rain showers and visibility between 6 and 7 NM. Because of the rain it was difficult to estimate the ceiling; but I thought I was more than 500 feet below the clouds. About 7NM west of [the hospital] I encountered Inadvertent IMC (IIMC). It happened extremely fast. I immediately transitioned to instruments. Once the aircraft was stable I initiated a turn to return to VMC. I maintained my cruising altitude as I turned. The Company IIMC Procedure calls for a climb to the MSA. The OAT indicated 3.5C and I did not want to risk climbing into icing conditions. I knew that my cruising altitude would keep me clear of all terrain and obstacles in the area; and I knew that there were VFR conditions behind me and to the North. Approximately 1-2 min later I returned to VMC.I marked the 'Reduced Safety Standards' Box above because I did not maintain the safety standard of cloud clearance and visibility for the class of airspace I was in.I was wearing Night Vision Goggles (NVGs) for the flight. It can be difficult to detect the extent of reduced visibility conditions while using NVGs. In the future I will periodically look under my goggles to help identify reduced visibility conditions in front of me. If I can identify the conditions sooner than I can deviate prior to entering the IMC. One final note. The Altitude and Heading Reference System (AHRS) 1 and the Auto Pilot were MEL'd for this flight. This increased my workload. In the future; when items that increase my workload are MEL'd I will increase my personal limitations for Ceiling and Visibility.

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.