Rough Air Over Tampa North
Carburetor ice in a marginal-climb airplane — the decision window is seconds, not minutes
The scenario
Departing Tampa North Aero Park Airport (X39), Tampa, FL — Runway 14, climbing out on a 141° heading. Elevation 68 ft MSL. 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 two miles to the northeast. Visibility 9 SM. Classic Gulf Coast conditions — warm, moist air, exactly the environment the FAA icing probability chart marks as 'serious icing at glide power, moderate icing at cruise power.'
You are 350 ft AGL, climbing through 68 KIAS (Vy for the C150M), heading 141°, when the engine begins to run rough. Power is noticeably down — the tachometer is unwinding. The off-field environment ahead is medium development, low-density development, and wooded wetland — not ideal for a forced landing, but workable. X39 is non-towered (CTAF); you are in Class G airspace below 3,000 ft MSL. Above 3,000 ft MSL, you would enter the overlying Tampa Class B.
Aircraft: Cessna 150M, solo, full fuel (18 gal usable), within limits. Continental O-200-A carbureted engine, 100 hp, fixed-pitch prop, fixed gear. This is a marginal-climb airplane — at gross weight in warm air, the climb rate is modest. 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 think about it. The C150M's climb performance is marginal; every knot of altitude feels like a win.
- {'label': 'Field', 'value': 'X39 · Tampa North Aero Park'}
- {'label': 'Runways', 'value': '14/32'}
- {'label': 'Elevation', 'value': '68 ft'}
- {'label': 'Aircraft', 'value': 'C150'}
- {'label': 'Dominant phase', 'value': 'Takeoff / Landing'}
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 in conditions conducive to serious icing, with insufficient time and altitude for carburetor heat to clear the accumulated ice. The pilot had not applied carburetor heat proactively in conditions that clearly warranted it.
NTSB ANC25LA005 (2024): A Cessna 150 on a personal flight experienced a 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. The probable cause was the pilot's failure to use carburetor heat in conditions conducive to the formation of carburetor ice.
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.
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 with no cultural lighting. 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.
All of these real accidents occurred at other airports — NOT at Tampa North Aero Park Airport (X39). X39's own dominant accident pattern is LOSS_OF_CONTROL_INFLIGHT (27.3%), LOSS_OF_CONTROL_GROUND (18.2%), and OBSTACLE_ON_TAKEOFF_LANDING (9.1%) — different failure modes, but the carburetor ice risk is the same in the warm, humid Gulf Coast environment.
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.
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 on the departure from X39, the decision window is measured in seconds — not minutes. The C150M's marginal climb performance means that once power is lost, recovery to the airport is difficult. Early recognition and immediate full carb heat is the entire lesson.
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 X39. 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.
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.
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 X39, the off-field environment on departure is poor — plan accordingly.
The off-field environment off Runway 14's departure end (heading 141°) is medium development, low-density development, and wooded wetland. There is no clear field, no open water for ditching, but a forced landing is possible if you pick the best surface (parking lot, road, or open ground). This is not a worst-case scenario; it is the geographic reality. Best glide is 60 KIAS. 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 14.
The C150M's marginal climb performance means that once power is lost, recovery is difficult.
The C150M has a best rate of climb (Vy) of 68 KIAS and a climb rate of roughly 400–500 fpm at sea level in standard conditions. In warm air (high density altitude), that rate drops significantly. At 350 ft AGL with a rough engine, you have very little altitude to work with. Early recognition of carburetor ice and immediate full carb heat is the entire lesson — waiting for the roughness to become obvious at 350 ft AGL is waiting too long.
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 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 is waiting too long.
Built from the real accident record
Scenario built from NTSB ERA25LA028, ANC25LA005, ERA24LA087 (C150 carburetor ice / delayed carb heat), WPR21LA329, CEN21LA381, ERA21LA284, and CEN23FA077 (C150 carb ice on takeoff/climb). Real events occurred at other airports — NOT at X39.
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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