Engine Roughness Over Tsala Apopka
Carburetor ice, progressive power loss, and a forced-landing decision in a C172N with good off-field options — but only if you act early
The scenario
Departing Brooksville–Tampa Bay Regional Airport (KBKV), Brooksville, FL — Runway 09, climbing out on a 090° heading. Elevation 76 ft MSL. It is a warm, humid Florida afternoon in late spring: OAT 27°C, dew point 21°C, altimeter 29.94. Scattered clouds at 2,800 ft, light rain shower one mile 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 600 ft AGL, climbing through 75 KIAS (near Vy of 73 KIAS), heading 090°, when the engine begins to run rough. Power is noticeably down — the tachometer is dropping. Off the Runway 09 departure end, the off-field environment is open developed land (parks, large lots), pasture, and medium development — good forced-landing terrain. KBKV's tower is part-time (0700–2200) and is open; you are in Class D airspace.
Aircraft: Cessna 172N, solo, full fuel, within limits. Carbureted Lycoming O-320, fixed-pitch prop, steam panel, fuel selector on BOTH. The airplane was airworthy at departure; nothing was written up. 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 220 hours total. You have flown the C172N for about 80 hours. You are familiar with KBKV but have not trained extensively on forced-landing decisions. You are on a local flight — no flight plan filed, no specific destination, just a local area check flight.
- {'label': 'Field', 'value': 'KBKV · Brooksville–Tampa Bay'}
- {'label': 'Runways', 'value': '3/21 · 9/27'}
- {'label': 'Elevation', 'value': '76 ft'}
- {'label': 'Aircraft', 'value': 'C172N'}
- {'label': 'Dominant phase', 'value': 'Landing / Cruise'}
The decision
Before we get into the decision tree — what do you already know about carburetor ice and forced-landing site selection in the C172N? (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 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. 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 lesson: even with carb heat applied, heavy ice accumulation in conducive conditions can overwhelm the heating system.
NTSB WPR15LA086 (2015): A Cessna 172N on an instructional flight over Molokai, Hawaii experienced partial loss of engine power during a climb over mountainous terrain and made a forced landing into densely forested terrain. The reason for the partial loss of engine power could not be determined because the aircraft was not recovered from the remote accident site. The lesson: forced-landing site selection is critical — dense forest is a last resort.
The real accidents cited above occurred at other airports and in other aircraft — NOT at Brooksville–Tampa Bay Regional Airport. KBKV has its own accident history (hard landings, runway excursions, and forced landings dominate the field's corpus), but these specific NTSB events happened elsewhere. The scenario is localized to KBKV 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 C172N 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. Off Runway 09 at KBKV, you have good off-field terrain (open developed land, pasture, medium development) — a forced landing there is survivable. But the better outcome is never needing it.
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, the decision window is measured in seconds — not minutes. Off Runway 09 at KBKV, the off-field environment is good (open developed land, pasture, medium development) — a forced landing there is survivable if you act early and fly the approach correctly.
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 KBKV. 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.
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. 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 KBKV Runway 09, the off-field environment is good — open developed land, pasture, and medium development.
Unlike some departure environments that are all water or dense forest, Runway 09's climb-out (heading 090°) offers good forced-landing terrain. Open developed land (parks, large lots), pasture, and medium development are suitable for a forced landing if the engine fails and altitude is insufficient to return to the airport. Know this terrain before you depart. Recognize it during the climb. If the engine fails, you have a survivable option — but only if you fly the approach correctly (65 KIAS best glide, doors unlatched, master off before impact, flaps for slowest touchdown speed).
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 27°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 600 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), ANC26LA001 (2025 C172N progressive power loss despite carb heat), and WPR15LA086 (2015 C172N partial power loss / forced landing). Localized to Brooksville–Tampa Bay Regional Airport (KBKV), Brooksville, FL.
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.
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