Date: 201712
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Icing; Rain; Snow; Turbulence; 10
Light: Night
Aircraft: PA-34-220T Turbo Seneca III
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B ZZZ; Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Valve/Oil System
Component problem: Malfunctioning
Reporter organization: Corporate
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Instrument
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Procedure; Aircraft; Weather
Primary problem: Weather

Narrative: I encountered Supercooled Large Droplets (SLD) icing conditions in my known ice certified Piper Seneca III. I began the flight on a direct route at 11;000 feet MSL. I noticed abnormally high oil temperature and lower than normal oil pressure on the right engine. After monitoring the engine instruments; the problem persisted and I made the decision to divert. I advised ATC of my situation and ATC cleared me direct ZZZ. I remained at 11;000 MSL as it was -24 degrees C and was helping keep the oil temperatures from exceeding the green arc on the gauge. As I neared ZZZ; the oil temperatures remained where they were; and I decided to continue on to ZZZ2 as it was closer to my final destination and I knew they had appropriate maintenance facilities on the field. There was a spotty band of light snow north of ZZZ2 that I observed on my XM weather radar; but ATC advised no reports of icing upon my inquiry. As I was approaching the class B airspace; ATC advised they would have to give me vectors around the departure corridor and instructed me to descend to 6;000 MSL. While descending; I entered IMC conditions and noted snow present in the clouds. Prior to encountering SLD conditions; only a trace of rime icing was noted on the leading edge of the de-ice boots. Approximately 5 minutes after entering IMC conditions; ATC advised he observed moderate precipitation at my 12 o'clock; about 6 miles in diameter; however no other aircraft had deviated; and no aircraft had reported any issues in the area. I assumed; as the OAT was -22 degrees C; that any precipitation would be snow and not cause an issue. As I descended below 8;000 MSL; I began encountering light turbulence. This turbulence for reasons unknown; fixed the abnormally high oil temperatures. Oil temperatures and pressures returned to normal and closely mirrored the left engine. Passing below 7;000 MSL; I heard heavy rain striking the windscreen. It sounded as if I was flying through moderate-heavy precipitation in the spring or summer. I looked at the OAT gauge and it read -21 degrees centigrade. I immediately initiated a 30 degree turn to the left; continued my descent; and advised ATC of my deviation. Approximately 30 seconds passed when I noticed an alarming amount of ice accretion on unprotected areas of the aircraft; including aft of the de-ice boots; and the side windows were beginning to freeze over. The sound of rain continued; and I continued my turn further to the left to attempt to fly out of what I realized was heavy freezing rain. At this time I noticed my airspeed beginning to rapidly decay. I pushed the nose down to 15 degrees in an attempt to increase my airspeed; but the airspeed continued to decay. Once the airspeed reached under 60 knots; I realized my pitot static system had frozen over. I confirmed that pitot heat was indeed on; (I turned pitot heat on prior to departing) as well as all other de-ice/anti-ice equipment. After I lost the airspeed indicator; The G500 began displaying red X's on the airspeed; heading; altitude; and attitude display. The only functioning instruments left were the standby attitude indicator; standby altimeter; and the whiskey compass. I engaged the alternate static source and [told] ATC. I told the controller I needed altitude readouts as quickly as he could get them to me; as I was flying blind in IMC in heavy freezing rain. The controller stated he showed me at 6;400 MSL level. I rolled in nose down trim and confirmed with the standby attitude indicator that I was in a descent. I checked the standby altimeter; and it was showing 6;400 MSL; but was not moving. I assumed it was unreliable and focused navigating by attitude and whiskey compass. I asked the Controllers for the ceiling in the area and he stated 4-5000 feet. I asked again for altitude readout and he stated 6;000 in a descent. I checked the leading edge of the wing for ice accretion and noticed a large ridge of ice forming behind the de-ice boots; but the bootsthemselves had significantly less ice accretion than other surfaces of the wing. There was run back ice on the top of the wing to the middle row of rivets on the wing. I continued my descent until around 4;500 MSL (estimated); where I exited the bottom of the clouds in a wings level; slightly nose down attitude. I informed the controller that I was in VMC conditions and no longer needed altitude readouts. The OAT outside of bottom of the clouds was -12 degrees centigrade and there was no precipitation present. Approximately one minute after exiting the clouds; the airspeed indicator came back alive and displayed a speed of 185 KIAS. Shortly thereafter; one by one all red X's on the G500 PFD went away and returned to normal operation. I descended to 4;000 MSL and confirmed the altitude with ATC. I continued operating the de-ice boots until the leading edges were free of the majority of ice contamination. The ice behind the protected surfaces was flying off the aircraft and I was maintaining altitude and airspeed normally. I accepted a heading turn from ATC; and advised I would like to stay on a heading; straight and level for some time to ensure the aircraft was performing normally. Once I had re-run the cruise and encountering severe ice checklists; the aircraft was operating normally; with no abnormal readings; including the right engine oil temperature and pressure. I told ATC that I would not advise them to have any traffic enter the clouds in the vicinity of the heavy freezing rain that I had encountered. As I still had some ice on the aircraft; I flew the approach at a higher than normal speed; with no flap extension. I completed the landing with no issue; and terminated the flight. I had learned of SLD icing from a video presentation; and was able to more readily identify those conditions and take corrective action. In hindsight; I should not have assumed that the precipitation reported by ATC was snow; just because I had been flying in snow and was not picking up any more than a trace of ice with an OAT of -21 degrees centigrade. Just because I was outside the 'normal' temperature window of icing conditions; does not mean that SLD conditions cannot be present. The next morning my mechanic and I tested the pitot and stall warning heat for proper operation. All components operated as designed; reaching a temperature of 205 degrees Fahrenheit. The aircraft has been grounded until the new oil control valve is installed.




Synopsis: PA34 pilot reported that supercooled liquid droplet icing conditions resulted in a loss of all flight instruments except for the standby attitude indicator and magnetic compass. Pilot exited icing conditions with ATC assistance and successfully diverted.