Rough Running Over Tampa Bay
Carburetor ice, partial power loss, and a water-surrounded airport with nowhere easy to go
The scenario
Departing Peter O Knight Airport (KTPF), Tampa, FL — Runway 04, heading 037°. Field elevation 8 ft MSL. You're on a local VFR sightseeing flight over Tampa Bay, solo, full fuel.
Aircraft: Cessna 172N, N-number familiar, within all limits. Carbureted Lycoming O-320, 160 hp. Steam gauges. Fixed gear. Fuel selector on BOTH.
Weather: Warm, humid Florida afternoon. OAT 28°C, dewpoint 22°C — a 6°C spread. Scattered cumulus at 3,500 ft, light haze, visibility 8 miles. ATIS mentions light rain showers in the area. Winds calm to light. These are textbook carburetor-icing conditions: high humidity, visible moisture, temperatures in the prime icing range.
Pilot: You — a Private pilot, about 120 hours total, comfortable in the 172N, but you've never actually experienced carburetor ice in flight. You've briefed the POH procedure, but it's never been real.
The situation: You departed Runway 04 and climbed northbound over the bay. At 1,500 ft MSL, roughly 1.5 nm north of KTPF, the engine begins to run rough. RPM drops about 150 rpm without any throttle input. The airplane is over open water — Hillsborough Bay — with the airport behind you and Tampa's built-up waterfront ahead.
- {'label': 'Field', 'value': 'KTPF · Peter O Knight'}
- {'label': 'Runways', 'value': '4/22 · 18/36'}
- {'label': 'Elevation', 'value': '8 ft'}
- {'label': 'Aircraft', 'value': 'C172N'}
- {'label': 'Dominant phase', 'value': 'Landing / Approach'}
The decision
The engine just got rough and RPM dropped. Before you act — what's actually in your head? (Pick all that apply — this records your mental model, not a grade.)
What the record shows
What the NTSB files show
NTSB CEN24LA362 (2024): A Cessna 172N on a local flight encountered light rain and carburetor ice at 1,800 ft AGL. 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 once applied. This accident did not occur at KTPF — it is used here because the airplane type, engine, and failure mode are identical to what you just flew.
NTSB CEN14LA276 (2014): A Cessna 172N on a cross-country experienced engine roughness and power loss in icing conditions. The pilot made a forced landing on an island where the aircraft nosed over in soft sand. Again — a different location, same airplane, same failure chain.
The Tampa Bay environment adds a layer the accident reports from other regions don't capture: at KTPF, every runway end except Runway 04 has open water off the departure end. Runway 22 (the preferred calm-wind landing runway) has Hillsborough Bay on short final. Runway 18 and Runway 36 both have water off their ends. A partial-power event at low altitude here is almost always a ditching decision, not a field-landing decision.
The regional precedent (ATL97LA099, a Cessna P210N ditching in the Gulf of Mexico) reinforces the same lesson: recognize engine failure symptoms early in the climb, commit to the ditching decision when altitude is insufficient for return, and execute a controlled ditching procedure. The airplane type is different; the decision geometry is the same.
The consistent NTSB finding across carb-ice accidents: pilots either did not apply carburetor heat at the first sign of roughness, or applied it too late after significant ice had accumulated. The procedure is simple — the discipline to execute it at the first symptom, before the situation degrades, is what separates a scare from an accident.
Key lesson — Carburetor heat is the FIRST response to unexplained engine roughness or RPM loss in a carbureted engine in conditions conducive to icing. At KTPF, where open water surrounds most runway ends, a partial-power event at low altitude is a ditching scenario — not a field-landing scenario. Act on the first symptom; don't wait for confirmation.
Debrief — teaching points
Carburetor ice is a weather event, not a mechanical failure — and it's predictable.
The Lycoming O-320 in the Cessna 172N is carbureted. The venturi effect in the carburetor throat drops air temperature by 20–30°F, which means ice can form at ambient temperatures well above freezing — typically between 20°F and 70°F with relative humidity above 50%. A dewpoint spread of 6°C (as in this scenario) on a warm, humid Florida afternoon is a textbook carb-ice setup. Check the carb-icing probability chart in the POH before every flight in these conditions, and use carburetor heat proactively during low-power operations (descents, pattern work).
Apply carburetor heat at the FIRST sign of roughness — not after you've ruled out everything else.
Unexplained RPM drop or engine roughness in a carbureted airplane in icing conditions means carburetor heat, full out, immediately. The engine will likely run rougher for 5–15 seconds as the ice melts and passes through — that is normal and expected. Do not pull the carb heat back in during this phase. If the roughness clears and RPM recovers, you've confirmed carb ice. If it does not improve after 30 seconds, you have a different problem — but you've eliminated the most common cause. Waiting to 'see if it clears on its own' allows ice to accumulate to the point where heat cannot clear it before power is lost.
At KTPF, engine failure at low altitude is almost always a ditching decision.
Peter O Knight Airport sits on a peninsula in Hillsborough Bay. Off Runway 22 (217°): open water. Off Runway 18 (173°): open water. Off Runway 36 (353°): open water and low-density development. Only Runway 04 (037°) offers any developed land off the departure end — and that environment is dense urban development, not a viable forced-landing surface. Know this before you depart. If the engine quits at low altitude over the bay, your job is a controlled ditching, not a search for a field. Mentally brief the ditching procedure on every departure from KTPF.
A controlled ditching at minimum speed is survivable — an uncontrolled one may not be.
If a ditching becomes necessary, the dominant priority is the slowest possible touchdown speed. Impact energy rises with the square of speed — touching down at 50 KIAS carries nearly 60% more energy than at 40 KIAS (Vs0). Establish 65 KIAS best glide to manage the descent, then transition to a flared touchdown as slow as possible — ideally near Vs0 (40 KIAS). Fly into wind if possible to reduce groundspeed. Transmit MAYDAY on 121.5 with position. Unlock doors before touchdown (water pressure can prevent opening). The airplane will float briefly — exit promptly.
One carb-ice event in icing conditions means the flight is over.
Clearing carburetor ice with carb heat and then continuing the flight into the same icing conditions is not a solution — it's a delay. If the conditions produced ice once, they will produce it again. The correct decision after a real carb-ice event is to return to the airport and land. This is not a conservative overreaction; it is the correct risk management. The NTSB files are full of second events that were worse than the first because the pilot continued flying.
Built from the real accident record
Scenario built from NTSB CEN24LA362 (2024 C172N carb-ice power loss), CEN14LA276 (2014 C172N forced landing), and regional ditching precedents ATL97LA099 and NYC03LA109. Anonymized and localized to KTPF.
NTSB reports: CEN24LA362 · CEN14LA276 · ERA09LA517 · ATL97LA099 · NYC03LA109
ACS tasks: PA.I.F — Weather Information · PA.I.H — Human Factors · PA.III.A — Maneuvering During Slow Flight · PA.IX.C — Emergency Approach and Landing · PA.IX.D — Emergency Equipment and Survival Gear
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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