Date: 201405
Local time of day: 0601-1200
Location: ZOA.ARTCC, CA
Flight conditions: Marginal
Weather elements / visibility: Icing; 10
Light: Daylight
Aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Descent
Airspace: Class E ZOA
ATC / advisory: Center ZOA
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Confusion; Situational Awareness; Training / Qualification; Workload
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Other / Unknown; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed As Precaution; General Declared Emergency
Contributing factors: Procedure; Human Factors; Weather
Primary problem: Weather

Narrative: My plan was a flight from the North Central California area to a plains State. The leg of the flight in question was over for fuel. I received my weather briefing in from DUATS. I reviewed the FAA TFR site. I reviewed the radar for the flight. Realizing there would be weather to contend with I made it a point to frequently review the weather along the route. I did note that there were limited weather reporting stations. I was weary that a complete picture of what was to be expected might not be available.I departed for a short flight to a fuel stop. I departed that airport without fuel approximately 30 minutes later due to temporarily unavailable fuel because of a fuel tanker delivery in progress. My original plan was to perform the trip under VFR and I filed a VFR flight plan though DUATS to my next stop. The aircraft is IFR certified and I am IFR qualified and current; flight total time 9;975 and current IFR charts are on board the aircraft. I departed a Central California airport and activated my VFR flight plan shortly thereafter through radio. I acknowledged the AIRMETS and Convective SIGMETS along the route. I also verified the freezing level for the route of flight to 7;500-8;800 MSL. I had an extensive conversation with Flight Watch shortly after activating the VFR flight plan as to the location of the embedded thunderstorms along the route and the current surface reports along the route. I was specifically monitoring an airport in the Nevada high desert. Its reports were approximately 7 SM and 3;600 overcast with some lower scattered layers. My thoughts were that although not ideal this would be adequate to proceed VFR. I also wrongly presumed as mentioned on the phone; that in the western arid higher altitude environment convective weather is usually isolated with limited wide spread areas of reduced visibility and mountain obscurement as commonly found in more humid lower elevation environments; usually providing more than adequate room for maneuvering well above the minimum VFR cloud and visibility regulations. This combined with the lack of weather reporting stations in the area allowed me to paint an inaccurate picture of the weather I was planning to expect. I have learned from this experience that this may not be the case. That the weather is not predictable and alternative plans should always be in place to address any unforeseen weather phenomenon. Over the Sierra foothills I executed a 180 degree turn as further flight would result in not being able to maintain minimum VFR cloud and visibility clearances. I noticed that the area of weather seemed to start and stop abruptly at foothills extending to the north and south. It was clear above just to the west and I elected to climb and see if the area of mountain obscurement could be over flown.Above 9;000 FT MSL I was in the clear between layers with the bases above estimated above in the flight levels. I obtained flight following through Oakland Center and had some difficulty reaching them directly. I obtained a relay from another aircraft to obtain the proper frequency. This in addition to the review of the low IFR enroute L-11 prompted my attention to the relatively high sector altitudes in the area. This is something I have learned from the experience; as high sector altitudes and MEA/MOCAs may result an aircraft of limited performance such as a single engine or a multi-engine with one engine failed to end up in a predicament should altitude not be able to be maintained. I was able to establish VFR flight following with Oakland. Visibility and cloud clearances were well above the minimum required; however; as a precaution; I though it prudent to arrange to pick up an IFR clearance in the event that conditions deteriorated. I wanted to ensure that the minimum sector altitudes that Oakland was able to provide were within the capabilities of the aircraft. I was expecting to traverse the area of higher terrain until northwest Nevada and then descendand continue VFR. I was monitoring the current local ASOS/AWOS as I progressed and from what I was hearing; especially at the high desert airport I was expecting the weather to improve. I had also thought of joining a Victor airway to take advantage of the lower MEA/MOCA's on the airway in order to exit the higher altitudes of decreased performance and increased headwinds. My ultimate objective was to descend to a lower altitude as soon as possible in accordance with what Center had available for minimum sector altitudes. I did not full appreciate until this incident how quickly a normal situation can deteriorate into an abnormal situation and I should have taken more aggressive steps to assure I had lower altitudes available for descent. There was no visible precipitation at this time and no indications of ice accruing on the aircraft. From the time the aircraft began to pick up ice to the time I began my descent to 12;000 and requested a 180 degree turn I estimated no more than 5 minutes had past. I elected to turn around due to the fact that the ice accumulation had only recently started. I predicted that I would be out of the situation just as fast as I had entered it. I realize now that by descending to a lower altitude while executing a course reversal I may have descended into more extensive icing conditions. The aircraft began shortly thereafter to exhibit classic signs of performance degradation with a lower than usual indicated airspeed. However; the performance loss seemed more rapid then I had seen before. Being familiar with the weather at the high desert airport I elected to divert direct to the VOR serving the airport. Center approved lower as requested. I was joining the 10 DME arc north west; west of the VOR when I realized with full power I was unable to maintain altitude. Observing the terrain under the lateral path and the added distance of the DME arc I was approved to proceed direct to the VOR. My plan was to position the aircraft within reach of the airport should the ice further exceed the performance capabilities of the aircraft. I took into account the missed approach procedure profile and holding pattern as well as the final approach fix and minimum descent altitudes. At this point it was apparent that Center had no way with in their protocol to issue an approach clearance as there is no initial approach fix at the VOR for the VOR/DME approach. They asked if I could accept the GPS approach which I replied that I could not. Looking back I see now that the straight VOR approach has the VOR as an IAF with slightly higher minimum altitudes. Had I requested that approach ATC could have issued the clearance. However; at the time I had formulated a plan based on the VOR/DME and thought it more prudent to concentrate on maneuvering the airplane and anticipating potential non-standard unpredictable ice related flying characteristics of the aircraft. Plus; it was unclear at the time whether I would have been able to maintain the published altitudes on either approach. It was for these reasons I elected to exercise my pilot in command authority to declare an emergency. I completed a teardrop entry to the missed approach hold in order to align myself on the final approach course. I was unable to maintain 8;800 FT for the arc but I was able to honor the straight in step downs prior to the FAF and the MDA. I circled the airport in visual conditions being able to maintain approximately 5;300 FT. After about two minutes the ice broke free from the aircraft. I was able to cancel IFR. I then landed uneventfully and am waiting for a significant improvement to the weather.




Synopsis: A single engine pilot attempted to fly over the Northern Sierra Nevada Mountains VFR. Enroute he picked up an IFR clearance in IMC but because of wing icing declared an emergency; began descending and diverted to a nearby airport below the initial approach altitude.