Rough Air Over Charlotte Harbor
Carburetor ice, partial power loss, and a non-towered field — the decision window is measured in seconds
The scenario
Departing Venice Municipal Airport (KVNC), Venice, FL — Runway 04, climbing out on a 045° heading over Charlotte Harbor. Elevation 18 ft MSL; the runway is essentially at sea level. KVNC is non-towered (CTAF 122.8); you are in Class G airspace.
It is a humid Florida morning in early summer: OAT 26°C, dew point 21°C, altimeter 29.94. Scattered clouds at 2,800 ft, light rain shower visible two miles to the northeast. Visibility 9 SM. Classic Gulf Coast conditions — warm, moist, and exactly the environment the FAA icing probability chart marks as 'serious icing at glide power, moderate icing at cruise power.' The relative humidity is 87%.
You are 350 ft AGL, climbing through 68 KIAS (Vy, best rate of climb), heading 045°, when the engine begins to run rough. Power is noticeably down — the tachometer is dropping. Charlotte Harbor fills the windscreen ahead and to the left. The airport is behind you. You are solo, within weight and balance limits, full fuel.
Aircraft: Cessna 150M, solo, full fuel (5.5 gallons usable per tank, 11 gallons total), within limits. Continental O-200-A carbureted engine, 100 hp, fixed-pitch prop, steam panel. Nothing was written up; the airplane was airworthy at departure.
Pilot: you — a Private pilot, current, roughly 180 hours total. You did not apply carburetor heat during the run-up because the engine ran smoothly. You did not apply it after takeoff because you were focused on the climb and did not anticipate icing conditions in 26°C air.
- {'label': 'Field', 'value': 'KVNC · Venice'}
- {'label': 'Runways', 'value': '4/22 · 13/31'}
- {'label': 'Elevation', 'value': '18 ft'}
- {'label': 'Aircraft', 'value': 'C150'}
- {'label': 'Dominant phase', 'value': 'Landing / Takeoff'}
The decision
Before we get into the decision tree — what do you already know about carburetor ice in the C150M? (Pick all that apply; this records your baseline.)
What the record shows
What the NTSB files show
NTSB ERA25LA028 (2024): A Cessna 150H encountered carburetor ice formation during cruise flight in conditions with 100% relative humidity and temperature/dew point spread conducive to serious icing. The engine ran rough and lost power. The probable cause was carburetor ice formation with the pilot's delayed use of carburetor heat while operating in icing conditions.
NTSB ANC25LA005 (2024): A Cessna 150 on a personal flight experienced partial loss of engine power due to carburetor ice formation during initial climb in conditions with 70% relative humidity conducive to serious icing at glide power. The probable cause was the pilot's improper use of carburetor heat while operating on Mogas in icing conditions.
NTSB ERA24LA087 (2024): A Cessna 150M on a solo cross-country instructional flight experienced partial engine power loss due to carburetor icing when the student pilot failed to apply carburetor heat. The accident resulted in a runway excursion during the diversionary landing.
NTSB CEN21LA381 (2021): A Cessna 150M experienced partial engine power loss due to carburetor icing during takeoff near Wadsworth, Ohio, when the pilot failed to apply carburetor heat despite conditions in the moderate-to-serious icing range. The pilot made a forced landing to a corn field where the aircraft nosed over. The pilot survived.
NTSB CEN23FA077 (2023, FATAL): A Cessna 150H on an instructional flight conducted a night visual approach to a non-towered airport in dark conditions. The aircraft descended below safe altitude and impacted a farm field 1.2 miles short of the runway. The probable cause was the flight instructor's failure to maintain control after a loss of engine power due to carburetor icing while maneuvering for forced landing in dark night visual meteorological conditions.
The real accidents cited above occurred at other airports and in other aircraft — NOT at Venice Municipal Airport. KVNC has its own accident history (see field dominant patterns: loss of control inflight, forced landings, spatial disorientation), but these specific carburetor icing events happened elsewhere. The scenario is localized to KVNC to make the off-field environment real and consequential for you as a student here.
The consistent thread across all these events: carburetor ice in the C150M is insidious. It builds gradually, the first symptom is roughness and a dropping tachometer (not a dramatic power cut), and by the time it is obvious, it may be too late for a comfortable recovery. The fix — full carburetor heat, immediately, at the first sign of roughness in conducive conditions — is simple. The failure is always a delay.
Key lesson — In warm, moist Gulf Coast air, the C150M's carbureted Continental O-200-A can accumulate serious carburetor ice even at cruise power and above-freezing temperatures. Apply full carburetor heat at the first sign of engine roughness or unexplained RPM loss. At low altitude over Charlotte Harbor, the decision window is measured in seconds — not minutes. Off Runway 04 at KVNC, the off-field environment is open water: a delayed response means a ditching, not a field landing.
Debrief — teaching points
Carburetor ice forms in conditions you would not expect.
The FAA icing probability chart shows 'serious icing at glide power' at temperatures between roughly 20°C and 30°C when relative humidity is high — exactly the Gulf Coast morning conditions at KVNC. You do not need visible ice, freezing temperatures, or IMC. Warm, moist air at reduced power is the classic carb-ice environment. The C150M's Continental O-200-A is carbureted; it has no alternate air system. Carburetor heat is the only tool. At 26°C OAT, 21°C dew point, and 87% relative humidity, the conditions are in the serious-icing range at glide power.
The first symptom is subtle — a dropping tachometer and engine roughness.
In a fixed-pitch airplane like the C150M, carburetor ice first shows as engine roughness and an unexplained RPM decrease. There is no dramatic power cut. Pilots who are not actively monitoring the tachometer miss the early warning. By the time the roughness is obvious, significant ice has accumulated. Scan the tachometer as part of your regular instrument scan, especially in conducive conditions. The C150M's 100 hp engine is already marginal on climb; any RPM loss is significant.
Apply full carburetor heat — not partial — and expect an initial RPM drop.
When you apply carb heat to an iced carburetor, the RPM will drop further before it rises. This is expected and normal: the heat is melting ice and the resulting water is briefly disrupting combustion. Do not remove carb heat when the RPM drops — that is the heat working. Hold it full on. The RPM will recover as the ice clears, typically within 15–30 seconds depending on ice accumulation. Partial carb heat can worsen the situation by partially melting ice into water ingestion without fully clearing the restriction.
At KVNC Runway 04, an engine failure on departure is a ditching.
The off-field environment off Runway 04's departure end (heading 045°) is open water — Charlotte Harbor. There is no alternate landing surface. If the engine quits on the Runway 04 departure and altitude is insufficient to return to the airport, the outcome is a ditching. This is not a worst-case scenario; it is the geographic reality. Best glide is 60 KIAS. Doors unlatched before water contact. Master off just before impact. Flaps for slowest possible touchdown speed — impact energy rises with the square of touchdown speed, so the slowest possible speed matters most. Know this before you line up on Runway 04.
Proactive carb heat use in conducive conditions is not optional.
The C150M POH and the FAA Pilot's Handbook of Aeronautical Knowledge both recommend applying carburetor heat when conditions are conducive to icing — before the symptom appears. In a Gulf Coast summer departure, with OAT near 26°C, dew point near 21°C, and relative humidity above 85%, that means applying carb heat during the run-up check (and confirming the expected RPM drop, then recovery) and considering its use during climb in visible moisture or high humidity. Waiting for the roughness to appear at 350 ft AGL over Charlotte Harbor is waiting too long.
Built from the real accident record
Scenario built from NTSB ERA25LA028, ANC25LA005, ERA24LA087, WPR21LA329, CEN21LA381, ERA21LA284, CEN23FA401, and CEN23FA077 — all Cessna 150-series carburetor icing and partial power loss events. Localized to KVNC, Venice, FL.
NTSB reports: ERA25LA028 · ANC25LA005 · ERA24LA087 · WPR21LA329 · CEN21LA381 · ERA21LA284 · CEN23FA401 · CEN23FA077
ACS tasks: PA.I.F — Weather Information · PA.I.G — Cross-Country Flight Planning · PA.IX.C — Emergency Approach and Landing · PA.I.H — Human Factors · PA.II.B — Engine Starting / Systems Preflight
Relevant FARs: §91.3 · §91.13 · §91.185
Step through the full decision tree, make the calls, and see where each choice leads — then debrief it with your CFI.
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