Date: 201205
Local time of day: 0001-0600
Location: SUN.Airport, ID
Flight conditions: Mixed
Weather elements / visibility: Icing; Rain; Thunderstorm; Turbulence; 10
Light: Daylight
Aircraft: Cessna Citation Mustang (C510)
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Initial Approach
Airspace: Class D SUN
ATC / advisory: Tower SUN
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Private
Human factors: Training / Qualification; Situational Awareness
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Weather
Primary problem: Human Factors

Narrative: During a flight to SUN; I was in contact with Salt Lake Center while descending toward SOLDE and thence PRESN Intersections to begin the RNAV (GPS) W Runway 31 approach into SUN airport. There was a GIII aircraft several minutes ahead of me on the approach that reported a cell of weather in the vicinity of the WTSOX Intersection (after PRESN on the approach profile). They further reported the airport was in sight and requested a visual approach into SUN in order to avoid the weather cell. The GIII crew warned ATC that any aircraft should avoid the cell as it was very intense and could be dangerous. I was in and out of IMC but I could see the tops of the cell they were referencing. I had my engine anti-ice system activated but was not picking up any airframe ice in the clouds. I also had acquired the cell painting yellow and red on my radar and NEXRAD displays in the cockpit. The cell appeared to be moving to the north-northeast and out of the RNAV approach profile so while I was concerned about the cell's proximity to my aircraft I thought I could safely fly the approach profile into visual conditions as did the GIII before me. As I neared PRESN I was cleared by ATC to begin the RNAV approach; told that radar services were terminated and to contact the Hailey Tower. I complied with these instructions and informed the Tower that I was on the GPS approach. Shortly after that; while passing PRESN and flying on autopilot towards WTSOX descending out of approximately 11;500 FT in IMC; I must have entered the storm cell. I encountered extreme turbulence; precipitation; and heavy icing. Fearing for the safety of the airplane I immediately engaged the autopilot heading mode and initiated a turn to the southeast; away from the center of the cell and towards what I knew to be visual conditions and lower terrain. My wing leading edges were loading up with ice and I turned on the airframe deice systems and monitored the activation of the system. I then increased my heading further towards the south in order to expedite my escape from the dangerous conditions. After a minute or two I exited the weather safely into visual conditions and began a turn back towards WTSOX and the airport. I was about to contact the Hailey Tower and inform them of the situation when they contacted me and requested my position and altitude. I gave them the information and told them I had deviated south of the approach path to escape the weather. I did not declare an emergency at that point because having safely exited the storm cell the emergency no longer existed. At that point I had the airport in sight and was about to request the visual approach when they instructed me to initiate a right turn back to PRESN; climb to 10;000 FT; and contact Salt Lake Center. I could see there were clouds and some virga over the south end of the airport so I decided it was prudent to fly back to PRESN as instructed by ATC to restart the RNAV approach. I then contacted Salt Lake Center with my position and they cleared me direct to PRESN at 10;000 FT and then a left 360 degree turn back to PRESN if needed before starting the RNAV GPS Runway 31 approach again. I was told by ATC I should not have been deviating to the south while on the approach earlier. I was too busy concentrating on safely flying the airplane and setting up for the new approach to explain to Center the exact nature of the emergency and sequence of events that caused me to deviate. I was cleared again for the approach; contacted the Tower as requested; and flew the approach into visual conditions. At this point the storm cell was no factor. I called the airport in sight just outside the LIBYO Intersection at 7;900 FT and landed safely. In hindsight I would have been better off if I had requested or been instructed to hold at the SOLDE Intersection or possibly PRESN (as published) to give more time for the weather cell to move away from the approach profile before at tempting to fly it. I was influenced to instead proceed with the approach by a few factors: a) The successful approach flown by the GIII just a few minutes ahead of me. b) The view outside the cockpit in the descent that appeared to indicate to me that visual conditions would be encountered shortly after beginning the approach.c) By the indications on my radar/NEXRAD display that the cell appeared to be moving off to the north of my flight path. I would have been helped greatly also if Salt Lake Center had been able to provide more assistance with respect to the position; movement; and intensity of the storm cell but I believe their radar coverage is not good in the vicinity of the Hailey airport. I also could have taken the time to talk to the GIII crew directly before initiating the approach to get a more complete description of the weather but I was too busy flying the airplane and they sounded as if they hand their hands full as well. This encounter is a good example of how dangerous even relatively small storm cells can be to the safe operation of aircraft. Even though I fly a multi engine turbine airplane equipped with excellent storm avoidance tools and anti-ice/deice systems; I was still taxed to nearly the limits of myself as PIC and those of the aircraft by inadvertently flying into this weather. Once I entered the storm cell I was so completely focused on safely escaping the conditions that I was unable initially to contact Hailey Tower and inform them of my situation and declare an emergency. I understand the serious requirement to inform ATC of any deviation from a clearance as per FAR 91.123; but in this emergency situation as pilot-in-command I had to first insure the safety and survival of the airplane and its occupants before any other distractions including a radio call. I was just at the point of being able to call the Tower when they contacted me first. I do not believe I could have called ATC sooner than I did and still be able to safely escape the conditions.




Synopsis: CE510 pilot inadvertently entered a thunderstorm during RNAV approach to SUN. Evasive action was taken by turning off the approach course away from the airport without advising ATC. Once contacted Tower advised to initiate a right turn back to PRESN; climb to 10;000 FT; and contact Salt Lake Center.