Date: 201403
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Icing; Turbulence; 5
Light: Daylight
Aircraft: Light Transport; High Wing; 2 Turboprop Eng
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Training
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Reporter organization: Personal
Reporter function: Instructor; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Situational Awareness; Troubleshooting
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Became Reoriented
Contributing factors: Aircraft; Weather
Primary problem: Weather

Narrative: ATC vectored me on a downwind for RWY XY; expecting to change to RWY XZ. We were vectored northwest of the airport and toward the lake. We had not encountered any ice up to this point at 11;000 FT MSL. Upon receiving an update that we would be using RWY XZ we continued our vectored heading. We were in IMC conditions at the time. Shortly afterwards I began to encounter moderate turbulence as I changed frequency. Shortly after the frequency change and call up the aircraft began picking up a substantial amount of clear ice and the aircraft began to make cracking noises (sounded like ice flinging off of props onto the aircraft). I looked out the window and saw that the engine cowling was completely covered with ice and the windshield was covered with clear ice as well. I made a call to ATC notifying them I was accumulating large amounts of clear ice and needed immediate vectors to the runway. They cleared me to 8;000 feet as an aircraft had just reported the bottoms there. I received a vector to the airport and rapidly descended with throttle at idle to the altitude; still seeing ice and IMC we were cleared down to 6;000; I began to see the terrain and that I was clear. As I looked at my altitude I realized that I was below 6;000 MSL as ATC announced the same. They asked if I could clear terrain; and I confirmed I could; we were then given vectors to the ILS and cleared to land visual on RWY XZ. The loss of situational awareness with altitude I connect with the priority to fly the aircraft to a safe non-icing altitude and the fact that I had disconnected the autopilot when I identified the icing condition. My mistake was to allow myself to be vectored over the lake in an aircraft that did not have anti-ice or deicing equipment in an area close to where a PIREP had reported intermittent light rime at 15;000 MSL.




Synopsis: While on vectors for landing; a pilot encountered an area where he picked up a substantial amount of clear ice and turbulence. He received a vector for the airport and a descent to get below the weather. However; he inadvertently descended below the cleared altitude. Fortunately; he was able to see the terrain and received clearance to land at his destination.