Skyhawk 172/Cutlass 172
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial
Flight Crew Last 90 Days 15; Flight Crew Total 2120; Flight Crew Type 1600
Workload; Time Pressure; Troubleshooting; Distraction; Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem
Weather; Aircraft; Human Factors
A standard weather briefing was received 30-45 minutes prior to departure of the flight via Foreflight. An area of forecasted freezing and precipitation was depicted in the area of the initial flight path. Departure and climb were normal; level flight at 9;000 MSL was IMC and continuous IMC and for a majority of the flight (4 hours; strong headwinds). Headwinds were strong (typically 30+ knots) in the northern portion of the route; but; turbulence was only light. Temperature at 9;000 was 35 degrees F with occasional moderate-heavy rain. ATC offered precautions about mod-heavy rain in the direction of the flight. Deviations to the East (initially) and then to the West were made to avoid heavier precipitation. No airframe structural icing was observed during the flight; but carburetor ice was experienced at 9;000 feet. The carburetor ice persisted even with carb heat on and caused a drop in RPM from 2;600-2;700 to the 2200-2300 range; significantly reducing available power and groundspeed. I was able to maintain the assigned 9;000 feet; but groundspeed dropped to mid-60 knots; in addition; the throttle 'froze' in position (almost full throttle). A decent was made from 9;000 to 7;000 feet with permission from ATC. Carburetor ice dissipated; the throttle responded; and normal power was restored. The remainder of the flight was un-eventful.I don't have good reasoning or excuse except to say that I was afflicted with some 'get-there-itis' while operating in these conditions; which should not have happened. I know better and should have exercised better judgment; for I put myself in a dangerous position and ATC in the awkward position of trying to help out a 'poor fool' - this is the part I am most ashamed of. 'Never again' are the operative words in this case.
A pilot of a light aircraft reported icing conditions where the application of carburetor heat was ineffectual; resulting in degraded engine performance. He requested a lower altitude and the icing threat dissipated and engine operation returned to normal.