Rough Climb Over Tampa Bay
Carburetor ice in a marginal-climb airplane — the decision window at 500 ft AGL is measured in seconds
The scenario
Departing St. Petersburg Clearwater International Airport (KPIE), Pinellas Park, FL — Runway 04, climbing out on a 040° heading. Elevation 11 ft MSL; the runway is essentially at sea level.
It is a humid Florida morning in early spring: OAT 22°C, dew point 18°C, altimeter 29.94. Scattered clouds at 2,800 ft, light rain shower one mile to the northeast. Visibility 9 SM. The temperature/dew point spread is 4°C — classic carburetor icing conditions at reduced power. The FAA icing probability chart marks this as 'serious icing at glide power.'
You are 500 ft AGL, climbing through 68 KIAS (Vy, best rate of climb for the C150), heading 040°, when the engine begins to run rough. Power is noticeably down — the tachometer is dropping. The water of Tampa Bay fills the windscreen ahead. KPIE's tower is active (0600–2300 local) and you are in Class D airspace.
Aircraft: Cessna 150M, solo, full fuel (18 gal usable), within limits. Carbureted Continental O-200-A, 100 hp, fixed-pitch prop, steam panel, fuel selector on BOTH. Nothing was written up; the airplane was airworthy at departure. The C150 is a marginal-climb airplane — at 500 ft AGL with a rough engine, you have very little altitude margin.
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 the engine sounded normal at full power.
- {'label': 'Field', 'value': 'KPIE · St. Petersburg Clearwater'}
- {'label': 'Runways', 'value': '4/22 · 18/36'}
- {'label': 'Elevation', 'value': '11 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 C150? (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 at cruise altitude in conditions with 100% relative humidity and a small temperature/dew point spread. 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 delayed applying carburetor heat despite the conducive conditions.
NTSB ANC25LA005 (2024): A Cessna 150 on a personal flight experienced partial engine power loss due to carburetor ice during initial climb in conditions with 70% relative humidity conducive to serious icing at glide power. The accident resulted from 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 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 accident was attributed to loss of engine power due to carburetor icing and the flight instructor's failure to apply carburetor heat.
The real accidents cited above occurred at other airports and in other aircraft — NOT at KPIE. KPIE has its own accident history dominated by loss-of-control events (21.2% of accidents) and stall/spin accidents (12.1%), but the specific carburetor ice events cited here happened elsewhere. The scenario is localized to KPIE 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 C150's marginal climb performance — especially at gross weight or in high density altitude — means that at 500 ft AGL with a rough engine, you have very little altitude margin. 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 Florida air with a small temperature/dew point spread, the C150'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 water, the decision window is measured in seconds — not minutes. Off Runway 04 at KPIE, the off-field environment is Tampa Bay: a delayed response means a ditching, not a field landing. The C150's marginal climb performance means altitude is your most precious resource.
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 15°C and 25°C when the temperature/dew point spread is small — exactly the morning conditions at KPIE. You do not need visible ice, freezing temperatures, or IMC. Warm, moist air at reduced power is the classic carb-ice environment. The C150'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 C150, 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 KPIE Runway 04, an engine failure on departure is a ditching.
The off-field environment off Runway 04's departure end (heading 040°) is open water — Tampa Bay. 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.
The C150 is a marginal-climb airplane — altitude is your most precious resource.
The C150 climbs at 68 KIAS (Vy) at sea level, but that climb performance degrades rapidly with weight, temperature, and density altitude. At 500 ft AGL with a rough engine, you have very little margin. A delay of 10–15 seconds in applying carb heat can cost you 100–150 ft of altitude — altitude you cannot afford to lose. At low altitude over water, the decision window is measured in seconds, not minutes. Recognize the problem and act immediately.
Built from the real accident record
Scenario built from NTSB ERA25LA028, ANC25LA005, ERA24LA087 (C150 carburetor ice / partial power loss), WPR21LA329, CEN21LA381, ERA21LA284, and CEN23FA077 (C150 carb ice in climb / forced landing). Real events occurred at other airports — NOT at KPIE.
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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