Engine Roughness Over Tampa Bay
Carburetor ice, power loss, and a forced-landing decision with water on three sides — every runway end matters
The scenario
Departing Peter O Knight Airport (KTPF), Tampa, FL — Runway 04, climbing out on a local VFR flight. Elevation 8 ft MSL. KTPF is a non-towered field (CTAF 122.8); you are in Class G airspace, but the overlying Tampa Class B (1,200 MSL to 10,000 MSL) is just above you.
It is a hazy Florida afternoon in late spring: OAT 28°C, dew point 22°C, altimeter 29.92. Scattered clouds at 2,500 ft, light rain shower one mile to the northeast. Visibility 8 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 C172N's carbureted Lycoming O-320 is particularly susceptible in these conditions.
You are 450 ft AGL, climbing through 73 KIAS (Vy), heading 037°, when the engine begins to run rough. Power is noticeably down — the tachometer is dropping. Off your left wing (north and west), dense development and medium development. Off your right wing (east), open water — Hillsborough Bay. Ahead (north), more development and water. Behind you (south), the airport and the runway you just left.
Aircraft: Cessna 172N, solo, full fuel, within limits. Carbureted Lycoming O-320, fixed-pitch prop, steam panel (attitude and heading vacuum-driven), fuel selector on BOTH. Nothing was written up; the airplane was airworthy at departure. 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 heads-down on the climb.
Pilot: you — a Private pilot, current, roughly 200 hours total. This is your first flight from KTPF; you are not familiar with the field's geography or the off-field environment. You did not brief the runway-end terrain before departure. You are now at 450 ft AGL with a rough engine and a decision window measured in seconds.
- {'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
Before we get into the decision tree — what do you already know about engine failure and forced landing at KTPF? (Pick all that apply; this records your baseline.)
What the record shows
What the NTSB files show
NTSB CEN24LA362 (2024): A Cessna 172N encountered light rain and carburetor ice at 1,800 feet 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. The pilot had not applied carburetor heat proactively in conditions that clearly warranted it.
NTSB CEN14LA276 (2014): A Cessna 172N on a cross-country flight experienced engine roughness and power loss at cruise altitude in conditions conducive to carb icing. The pilot made a forced landing on an island; the aircraft nosed over in soft sand. The pilot survived. The probable cause could not be determined due to premature aircraft release — but the conditions and symptoms are consistent with carburetor ice.
NTSB ANC26LA001 (2025): A Cessna 172 on an instructional flight experienced progressive engine power loss during training maneuvers despite carburetor heat application. The pilot made a forced landing on a road; the aircraft struck a rock during landing roll and nosed over. Atmospheric conditions indicated serious icing conditions in pressure-type carburetors — the ice was heavy enough that a single application of carb heat was insufficient.
NTSB CEN14LA374 (2014): A Cessna 172N on a personal local flight experienced partial engine power loss during cruise and made a forced landing to a cornfield. The accident resulted from partial loss of engine power due to failure of the dual magneto system caused by loose mounting screws, with improper maintenance during the annual inspection as a contributing factor. Not all engine failures are carb ice — some are mechanical.
The real accidents cited above occurred at other airports and in other aircraft — NOT at Peter O Knight Airport. KTPF has its own accident history dominated by forced landings (19.4%), loss of control (16.7% inflight, 11.1% ground), ditching (11.1%), and stall/spin (8.3%). The scenario is localized to KTPF to make the off-field environment real and consequential for you as a student here.
KTPF's geography is unforgiving: off Runway 22, 18, and 36, the primary off-field option is open water — Hillsborough Bay and the surrounding waterways. Off Runway 04, the environment is dense development and medium development — poor forced-landing options. An engine failure on the Runway 04 departure at low altitude is a marginal situation; an engine failure on Runway 22, 18, or 36 departures is a ditching. This is not hypothetical; it is the USGS NLCD ground cover off each runway end.
The consistent thread across all these events: engine failures in the C172N are survivable if the pilot recognizes the problem early, applies the correct immediate response (carb heat for icing, fuel selector / mixture for starvation, magneto check for electrical failure), and makes a sound forced-landing decision. The failure is always a delay — waiting for the problem to get worse, waiting for the engine to quit completely, waiting too long to turn back to the airport.
Key lesson — In warm, moist Gulf Coast air, the C172N's carbureted O-320 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 KTPF, the decision window is measured in seconds — not minutes. Off Runways 22, 18, and 36, the off-field environment is open water: a delayed response means a ditching, not a field landing. Off Runway 04, the environment is dense development: a delayed response means a forced landing into an urban area. Know the terrain 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 afternoon conditions at KTPF. You do not need visible ice, freezing temperatures, or IMC. Warm, moist air at reduced power is the classic carb-ice environment. The C172N's Lycoming O-320 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 C172N, 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 450 ft AGL on the Runway 04 departure, you have roughly 30 seconds before altitude becomes critical. Early recognition is survival.
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.
KTPF's off-field environment is water and development — know which runway you are on.
Off Runway 04 (climb-out heading 037°), the off-field environment is dense development and medium development — poor forced-landing options. Off Runways 22, 18, and 36, the primary off-field option is open water — Hillsborough Bay. An engine failure on the Runway 04 departure at low altitude is a marginal situation; an engine failure on Runway 22, 18, or 36 departures is a ditching. This is not hypothetical; it is the USGS NLCD ground cover. Know the terrain before you line up on the runway.
Best glide is 65 KIAS. Establish it immediately if power is lost.
Best glide speed for the C172N is 65 KIAS at gross weight. This speed maximizes glide distance and gives the most time and distance to manage the emergency. At 450 ft AGL over KTPF, establishing 65 KIAS immediately maximizes your options — whether that means reaching the airport or setting up the best possible controlled ditching. Do not try to stretch the glide with a shallower pitch; you will stall. Fly 65 KIAS.
Proactive carb heat use in conducive conditions is not optional.
The C172N 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 28°C and dew point near 22°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 450 ft AGL is waiting too long.
Built from the real accident record
Scenario built from NTSB CEN24LA362 (2024 C172N carburetor ice / power loss), CEN14LA276 (2014 C172N engine roughness / forced landing), ERA09LA517 (2009 C172N total power loss), ANC26LA001 (2025 C172N progressive power loss despite carb heat), WPR15LA086 (2015 C172N partial power loss / forced landing), CEN14LA374 (2014 C172N magneto failure / forced landing), WPR14LA099B (2014 fuel contamination / forced landing), and WPR12LA306 (2012 C172N exhaust valve failure / forced landing). Anonymized and localized to KTPF.
NTSB reports: CEN24LA362 · CEN14LA276 · ERA09LA517 · ANC26LA001 · WPR15LA086 · CEN14LA374 · WPR14LA099B · WPR12LA306
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.
Open the interactive scenario →All sample scenarios · More Cessna 172N scenarios · More scenarios at KTPF