Rough Climb Over Clearwater
Carburetor ice in a marginal-climb airplane — dense development off both runway ends means every second counts
The scenario
Departing Clearwater Air Park (KCLW), Clearwater, FL — Runway 16, climbing out on a 155° heading. Elevation 71 ft MSL. You are a Private pilot with roughly 180 hours total time, current and proficient in the Cessna 150M.
It is a warm, humid Florida morning in late spring: 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. The conditions are textbook for carburetor icing: high humidity, temperature/dew point spread of only 5°C, and visible moisture. The FAA icing probability chart marks this as 'serious icing at glide power, moderate icing at cruise power.'
You are 350 ft AGL, climbing through 68 KIAS (Vy, best rate of climb for the C150M), heading 155°, when the engine begins to run rough. The tachometer is unwinding — you are losing RPM. The airplane is still climbing, but the climb rate is noticeably shallower. Off the Runway 16 departure end, the off-field environment is dense development: residential neighborhoods, low-density development, medium-density development. There is no open field, no water, no park. The developed area is the only option ahead.
Aircraft: Cessna 150M, solo, full fuel (18 gal usable), within limits. Continental O-200-A, carbureted, fixed-pitch prop, steam panel, fuel selector on BOTH. Nothing was written up; the airplane was airworthy at departure.
Pilot: you — Private pilot, current, 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 the conditions would be conducive to icing at this low altitude.
- {'label': 'Field', 'value': 'KCLW · Clearwater Air Park'}
- {'label': 'Runways', 'value': '16/34'}
- {'label': 'Elevation', 'value': '71 ft'}
- {'label': 'Aircraft', 'value': 'C150'}
- {'label': 'Dominant phase', 'value': 'Landing / Approach'}
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 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 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 150 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.
NTSB ERA21LA284 (2021): A Cessna 150 instructional aircraft lost engine power during takeoff due to carburetor icing and made a forced landing into trees near Elba, Alabama. The accident resulted from carburetor ice formation under atmospheric conditions conducive to serious icing at glide power, with contributing factors including insufficient time to melt accumulated ice despite carburetor heat application.
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 Clearwater Air Park. KCLW has its own accident history (see field dominant patterns: forced landing 22.2%, loss of control inflight 18.5%, gear-up landing 18.5%), but these specific carburetor icing events happened elsewhere. The scenario is localized to KCLW 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 C150 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. In the C150M, a marginal-climb airplane, losing even partial power on initial climb is a serious threat. Off Runway 16 at KCLW, the off-field environment is dense development: there is no open field, no water, no park. A forced landing in residential terrain is survivable if flown correctly (best glide, slowest touchdown speed), but prevention is always better.
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 dense development, the decision window is measured in seconds — not minutes. The C150M is a marginal-climb airplane; losing power on initial climb is a critical threat. Know the off-field environment off each runway end before you depart.
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 KCLW. 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. Scan the tachometer as part of your regular instrument scan, especially in conducive conditions.
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. At 350 ft AGL on initial climb, a 20–30 second delay in recognizing and responding to the symptom can mean the difference between a clean recovery and a forced landing.
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.
The C150M is a marginal-climb airplane — losing power on initial climb is a critical threat.
The C150M has only 100 hp and a best rate of climb (Vy) of 68 KIAS. At gross weight, in heat, or at high density altitude, climb performance is marginal. Losing even 50–100 RPM on initial climb can mean the difference between climbing away and maintaining altitude. Off Runway 16 at KCLW, the off-field environment is dense development: residential neighborhoods, low-density and medium-density development. There is no open field, no water, no park. A forced landing in developed terrain is survivable if flown correctly, but it is not the outcome you want. Recognize carb ice early and recover it before it becomes critical.
Proactive carb heat use in conducive conditions is not optional.
The C150 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 and dew point near 21°C, 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 dense development is waiting too long.
Built from the real accident record
Scenario built from NTSB ERA25LA028, ANC25LA005, ERA24LA087, WPR21LA329, CEN21LA381, ERA21LA284, and CEN23FA077 — all Cessna 150-series carburetor icing events. Localized to KCLW.
NTSB reports: ERA25LA028 · ANC25LA005 · ERA24LA087 · WPR21LA329 · CEN21LA381 · ERA21LA284 · 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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