Date: 201604
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: Marginal
Weather elements / visibility: Fog; Rain; 4
Light: Daylight
Aircraft: Cheetah; Tiger; Traveler AA5 Series
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Cruise
Airspace: Class G ZZZ
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Anomaly: Inflight Event / Encounter VFR In IMC; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Exited Penetrated Airspace; Flight Crew Landed As Precaution; Flight Crew Diverted
Contributing factors: Human Factors; Weather
Primary problem: Weather

Narrative: Transiting south under VFR conditions with rain in the area. IFR was decided against due to high terrain; airplane performance; and possible ice at airway altitudes. NEXRAD (Next-Generation Radar) weather displayed on phone app. Aircraft WAAS-GPS (Wide Area Augmentation System) equipped with terrain awareness system. Weather behind was clear with high ceilings and terrain was dropping. My plan was to move airport to airport if the weather was ever in question; taking a look-see and retuning if conditions were marginal. Weather was VMC with high ceilings and showers in the vicinity; and I was flying at approximately 1;000ft AGL. I told my non-pilot (but professional cockpit aircrew) passenger to keep an eye on the terrain display while I remained visual and watched the weather. We briefed flying on the west side of the valley and always keeping a turn-out option to the left (pilot flying side). Closest airport was calling VMC with high clouds. NEXRAD showed precipitation; but sunlight could be seen on the horizon ahead. At South the visibility in light rain and mist dropped to estimated 3 miles and I descended over the highway to maintain orientation. We both pointed out power lines and I called out specific intentions. I slowed to approximately 100 KIAS. Then I descended below terrain to our left and upon realizing the turn-out restriction I stated; 'If this gets any worse we'll make an emergency landing on the southbound highway' and; 'these are helicopter altitudes I'm familiar flying at.' As the sunlight increased on my left I flew more easterly and began setting up for landing; at one point briefly crossing into restricted airspace which my passenger pointed out and I turned back right. We landed in clear conditions and discussed what went wrong and whether we should continue. Because of worsening weather at our destination; we drove home from the airport where we landed. The electronic tools certainly assisted. Get-home-itis was not a major factor since we had no events and had already decided driving the last distance was likely. I believed I was familiar with the terrain because of years driving in the area; but I followed the weather lower than ever intended and was drawn to the light on the horizon.




Synopsis: Grumman American AA-5 pilot reported flying in VFR conditions when the weather closed in and they found themselves in IMC.