Narrative:

Forecast WX was to be VFR for duration of the medical transport flight. Outbound leg was uneventful. Visibility and ceilings matched the reported VMC WX conditions. After 1 hour delay on the deck at hospital helipad; aircraft departed VFR on a company flight plan using night vision goggle devices. Airports along the route of flight reported visibility 10 mi with variable cloud coverage (sct 014 ovc 050 to the west; sct 040 ovc 100 to the north; broken 011 broken 095 to the east; and ovc 014 to the southeast). Patients gain improved oxygen saturation when flying at lower altitudes. Given the reported WX; I chose to hug the shoreline and fly below the clouds in VMC conditions. The night vision goggles provided good visual contact with the adjacent shoreline and distant shorelines to the east. Onboard avionics provided outstanding positional and terrain situational awareness. Flying over the water at 1000 ft AGL the aircraft began to encounter scattered clouds at or above altitude with a reduction in visibility due to light rain (typical convergence zone activity). I began a descent below 700 ft AGL and rechked en route WX using local ATIS/ASOS and found that the surface dew point spread had closed to less than 3 degrees. Frequency of clouds at altitude worsened. Despite my good situational awareness and ground references; I felt the time for maneuvering in VMC had expired. Reversing course meant turning out to sea where there was no ground reference. Turning inland would result in reduced terrain clearance. I contacted the area approach control facility; declared an emergency due to iimc and requested immediate climb and vectors for VFR on top with follow on ILS approach so as to facilitate completion of the medical transport. Support from the agency was timely and accurate. Upon reflection; I realize it would have been much wiser to obtain an en route clearance at the time of departure. I am common with the procedure and have employed it before as a tool in my pilot's IFR 'bag of tricks' when encountering unreported WX. In this particular case; I was comfortable in continuing under VFR; drawing from my many yrs of military experience with 'aided' flight. The goggles allowed me to see clouds and surface lighting that was well beyond the unaided visual range. Had I not been wearing the devices; I most likely would not have continued to proceed in the direction I was going without an IFR clearance due to my inability to 'see' the WX and lights ahead. Could I have safely pushed ahead and flown beyond the convergence zone WX phenomena to the reported VMC east of my position? Yes; I believe so; but not legally. Integrity and professionalism was the motivation to officially declare iimc and receive assistance. In the future I will ask for that assistance sooner allowing for a greater margin of safety. My advice for those that employ night vision devices is to leave them out of your preflight WX decision making process; take an occasional look beneath them during cruise flight to assess the situation; know your goggles' limitations and use it to make informed WX decisions to avoid your own inadvertent IMC emergency.

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Original NASA ASRS Text

Title: A109 PLT WAS FLYING AT NIGHT IN DETERIORATING WX. CEILINGS BECAME LOWER AND PLT DECLARED EMER TO CLIMB THROUGH OVERCAST AND OBTAIN VFR ON TOP CLRNC.

Narrative: FORECAST WX WAS TO BE VFR FOR DURATION OF THE MEDICAL TRANSPORT FLT. OUTBOUND LEG WAS UNEVENTFUL. VISIBILITY AND CEILINGS MATCHED THE REPORTED VMC WX CONDITIONS. AFTER 1 HR DELAY ON THE DECK AT HOSPITAL HELIPAD; ACFT DEPARTED VFR ON A COMPANY FLT PLAN USING NIGHT VISION GOGGLE DEVICES. ARPTS ALONG THE RTE OF FLT REPORTED VISIBILITY 10 MI WITH VARIABLE CLOUD COVERAGE (SCT 014 OVC 050 TO THE W; SCT 040 OVC 100 TO THE N; BKN 011 BKN 095 TO THE E; AND OVC 014 TO THE SE). PATIENTS GAIN IMPROVED OXYGEN SATURATION WHEN FLYING AT LOWER ALTS. GIVEN THE REPORTED WX; I CHOSE TO HUG THE SHORELINE AND FLY BELOW THE CLOUDS IN VMC CONDITIONS. THE NIGHT VISION GOGGLES PROVIDED GOOD VISUAL CONTACT WITH THE ADJACENT SHORELINE AND DISTANT SHORELINES TO THE E. ONBOARD AVIONICS PROVIDED OUTSTANDING POSITIONAL AND TERRAIN SITUATIONAL AWARENESS. FLYING OVER THE WATER AT 1000 FT AGL THE ACFT BEGAN TO ENCOUNTER SCATTERED CLOUDS AT OR ABOVE ALT WITH A REDUCTION IN VISIBILITY DUE TO LIGHT RAIN (TYPICAL CONVERGENCE ZONE ACTIVITY). I BEGAN A DSCNT BELOW 700 FT AGL AND RECHKED ENRTE WX USING LCL ATIS/ASOS AND FOUND THAT THE SURFACE DEW POINT SPREAD HAD CLOSED TO LESS THAN 3 DEGS. FREQUENCY OF CLOUDS AT ALT WORSENED. DESPITE MY GOOD SITUATIONAL AWARENESS AND GND REFS; I FELT THE TIME FOR MANEUVERING IN VMC HAD EXPIRED. REVERSING COURSE MEANT TURNING OUT TO SEA WHERE THERE WAS NO GND REF. TURNING INLAND WOULD RESULT IN REDUCED TERRAIN CLRNC. I CONTACTED THE AREA APCH CTL FACILITY; DECLARED AN EMER DUE TO IIMC AND REQUESTED IMMEDIATE CLB AND VECTORS FOR VFR ON TOP WITH FOLLOW ON ILS APCH SO AS TO FACILITATE COMPLETION OF THE MEDICAL TRANSPORT. SUPPORT FROM THE AGENCY WAS TIMELY AND ACCURATE. UPON REFLECTION; I REALIZE IT WOULD HAVE BEEN MUCH WISER TO OBTAIN AN ENRTE CLRNC AT THE TIME OF DEP. I AM COMMON WITH THE PROC AND HAVE EMPLOYED IT BEFORE AS A TOOL IN MY PLT'S IFR 'BAG OF TRICKS' WHEN ENCOUNTERING UNREPORTED WX. IN THIS PARTICULAR CASE; I WAS COMFORTABLE IN CONTINUING UNDER VFR; DRAWING FROM MY MANY YRS OF MIL EXPERIENCE WITH 'AIDED' FLT. THE GOGGLES ALLOWED ME TO SEE CLOUDS AND SURFACE LIGHTING THAT WAS WELL BEYOND THE UNAIDED VISUAL RANGE. HAD I NOT BEEN WEARING THE DEVICES; I MOST LIKELY WOULD NOT HAVE CONTINUED TO PROCEED IN THE DIRECTION I WAS GOING WITHOUT AN IFR CLRNC DUE TO MY INABILITY TO 'SEE' THE WX AND LIGHTS AHEAD. COULD I HAVE SAFELY PUSHED AHEAD AND FLOWN BEYOND THE CONVERGENCE ZONE WX PHENOMENA TO THE REPORTED VMC E OF MY POS? YES; I BELIEVE SO; BUT NOT LEGALLY. INTEGRITY AND PROFESSIONALISM WAS THE MOTIVATION TO OFFICIALLY DECLARE IIMC AND RECEIVE ASSISTANCE. IN THE FUTURE I WILL ASK FOR THAT ASSISTANCE SOONER ALLOWING FOR A GREATER MARGIN OF SAFETY. MY ADVICE FOR THOSE THAT EMPLOY NIGHT VISION DEVICES IS TO LEAVE THEM OUT OF YOUR PREFLT WX DECISION MAKING PROCESS; TAKE AN OCCASIONAL LOOK BENEATH THEM DURING CRUISE FLT TO ASSESS THE SITUATION; KNOW YOUR GOGGLES' LIMITATIONS AND USE IT TO MAKE INFORMED WX DECISIONS TO AVOID YOUR OWN INADVERTENT IMC EMER.

Data retrieved from NASA's ASRS site as of January 2009 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.