Cessna 400
Flight Crew Private; Flight Crew Instrument
Flight Crew Last 90 Days 54; Flight Crew Total 1346; Flight Crew Type 656
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Human Factors; Weather
I filed for 13;000 MSL and ATC wanted a climb to 15;000 for mountain clearance. (13;000 was VMC and 15;000 was IMC) At 15;000 I began picking up some rime ice (temp was -4C) so engaged my TKS system and pitot heat. TKS took a few minutes to work and since airspeed decreased 10 knots and more; I tried to contact ATC to request lower. Since I could not contact ATC; another pilot radioed my request to descend to 13;000 and ATC did not want to allow. I said I had on-board terrain information and would be responsible for terrain clearance. I then told him I was descending to 13;000 to get out of clouds and he said I could have a VFR on top clearance which I accepted and came down to 13;000. I was now out of clouds and TKS was removing ice; so after I was past the clouds I requested a climb back to 15;000 and rest of flight had no problems. I was given a number to call after landing which I called to explain situation and he did a good job of explaining why the MVA was 15;000 where I was flying.This problem was caused by ATC requiring me to climb to 15;000 and I now understand why. I'm thankful my plane has a TKS system which helped remove the ice and prevent additional build-up. In the future I will avoid flying in clouds at -4C by requesting a deviation to clear clouds horizontally or by requesting vectors to remain at a VMC altitude authorized by ATC.
Columbia 400 pilot reported he was picking up ice and unable to maintain altitude. Pilot descended below MVA to get clear of clouds.