Power Loss on Base — Brooksville
Partial engine failure in the traffic pattern: carburetor ice, a marginal climb airplane, and the decision to continue or land
The scenario
Departing Brooksville–Tampa Bay Regional Airport (KBKV), Brooksville, FL — Runway 09, a 7,001 ft concrete runway. Elevation 76 ft MSL. You are a Private pilot with roughly 180 hours total time, current and proficient. This is a local VFR flight in a Cessna 172M — the lower-powered 150 hp variant, not the newer 172N. The 172M is a marginal climber, especially in heat and at gross weight.
It is a warm, humid Florida afternoon in late May: OAT 28°C (82°F), dew point 21°C (70°F), altimeter 29.92. Scattered clouds at 2,500 ft, light rain shower two miles to the northeast. Visibility 8 SM. The conditions are textbook for carburetor icing: the FAA icing probability chart marks this as 'serious icing at glide power, moderate icing at cruise power.' The 172M's carbureted Lycoming O-320 is particularly susceptible.
You have completed a local flight and are returning to KBKV. Tower is active (part-time, 0700–2200 local; it is 1530 local). You are in Class D airspace. You have been cleared for a straight-in approach to Runway 09. You are on base turn at 800 ft AGL, airspeed 75 KIAS (approach speed is 63 KIAS; you are a bit fast), and the engine begins to run rough. The tachometer is unwinding. You are 1.5 nm from the runway threshold.
Aircraft: Cessna 172M, solo, 2,200 lb (near gross), full fuel, within limits. Carbureted Lycoming O-320, 150 hp, fixed-pitch prop, steam panel. 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 during cruise because you were not thinking about it — the conditions were not obviously icing-conducive to you.
Pilot: you — a Private pilot, current, roughly 180 hours total. You have flown the 172M before, but this is your first experience with an in-flight engine anomaly. You are on base turn, 800 ft AGL, 1.5 nm from the runway. The decision window is measured in seconds.
- {'label': 'Field', 'value': 'KBKV · Brooksville–Tampa Bay'}
- {'label': 'Runways', 'value': '3/21 · 9/27'}
- {'label': 'Elevation', 'value': '76 ft'}
- {'label': 'Aircraft', 'value': 'C172M'}
- {'label': 'Dominant phase', 'value': 'Landing / Cruise'}
The decision
Before we get into the decision tree — what do you already know about the C172M's engine and carburetor icing? (Pick all that apply; this records your baseline.)
What the record shows
What the NTSB files show
NTSB ERA09LA379 (2009): A Cessna 172M student pilot on a solo instructional flight experienced engine power loss during the base-to-final turn in the traffic pattern at an uncontrolled field. The ambient conditions (75°F OAT, 55°F dew point) were conducive to serious carburetor icing per the FAA icing probability chart. The pilot made a forced landing in a field. The probable cause was carburetor icing at glide power.
NTSB CEN24LA168 (2024): A Cessna 172M on an IFR flight experienced engine power loss due to carburetor icing during descent in night IMC. The pilot touched down on a building roof and impacted a retaining wall and ground. The probable cause was the pilot's delayed use of carburetor heat, which resulted in ice accumulation beyond the point where heat could restore full engine power.
NTSB CEN22LA181 (2022): A Cessna 172M on a personal flight experienced partial engine power loss during a go-around attempt from a low approach to an upsloping turf runway. The probable cause was the pilot's failure to use carburetor heat during the approach and an unsuitable flight profile for the runway configuration.
NTSB CEN22LA309 (2022): A Cessna 172M experienced engine power loss during cruise flight due to a stuck exhaust valve. The pilot performed a forced landing in a field, resulting in substantial fuselage damage.
NTSB WPR13LA035 (2012): A Cessna 172M on an aerial photography mission experienced a loss of engine power when the pilot applied full throttle during climb. The probable cause was failure of the throttle control cable outer jacket, which fragmented and prevented proper throttle control.
The real accidents cited above occurred at other airports and in other aircraft types — NOT at Brooksville–Tampa Bay Regional Airport. KBKV has its own accident history (see field dominant patterns: hard landing 26.9%, forced landing 11.5%, runway excursion 11.5%), 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 icing in the C172M 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. The C172M's 150 hp engine is also marginal for a go-around at gross weight in heat; if you must go around, do it early and with full power available.
Key lesson — In warm, moist Gulf Coast air, the C172M'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. In the traffic pattern at low altitude, the decision window is measured in seconds — not minutes. Off Runway 09 at KBKV, the off-field environment is mostly open developed areas and pasture; a forced landing there is workable. But the better call is to recognize carb ice early, apply heat immediately, and land with full power available.
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 C172M's Lycoming O-320 is carbureted; it has no alternate air system. Carburetor heat is the only tool. The 172M is also a marginal climber at gross weight in heat — if you must go around, do it early.
The first symptom is subtle — a dropping tachometer and engine roughness.
In a fixed-pitch airplane like the C172M, 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. On base turn at 800 ft AGL, you should be scanning power, altitude, and descent rate — the tachometer drop is your early warning.
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, the off-field environment off each runway end is workable for a forced landing.
Off Runway 09's climb-out (heading 90°), the off-field environment is mostly open developed areas (parks, large lots), pasture/hay, and medium development — not ideal, but workable for a forced landing. Off Runway 03's climb-out (heading 26°), the environment is similar: pasture, open developed areas, medium development. Off Runway 21's climb-out (heading 206°), the environment is evergreen forest and pasture. Off Runway 27's climb-out (heading 270°), the environment is low-density development and grassland. None of these are water. A forced landing at KBKV is a field landing, not a ditching. Know the off-field environment for each runway you use.
The C172M is a marginal climber — plan go-arounds carefully.
The C172M has 150 hp, not the 160 hp of the 172N. At gross weight, in heat, or at high density altitude, the 172M climbs slowly. A go-around at 500 ft AGL with a degraded engine is a risky maneuver. If you must go around, do it early — at 800 ft AGL or higher — and with full power available. If the engine is rough or losing power, a go-around may not be the right call; a stable descent to the runway at best glide speed may be safer.
Proactive carb heat use in conducive conditions is not optional.
The C172M 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 approach, with OAT near 28°C and dew point near 21°C, that means considering carb heat during the descent in visible moisture or high humidity. Waiting for the roughness to appear at 800 ft AGL on base turn is waiting too long.
Built from the real accident record
Scenario built from NTSB ERA09LA379 (2009 C172M carburetor ice on base turn), CEN24LA168 (2024 C172M delayed carb heat / night IMC power loss), CEN22LA309 (2022 C172M stuck exhaust valve / forced landing), CEN22LA181 (2022 C172M carb heat failure / go-around accident), and WPR13LA035 (2012 C172M throttle cable failure). Localized to Brooksville–Tampa Bay Regional Airport (KBKV).
NTSB reports: ERA09LA379 · CEN24LA168 · CEN22LA309 · CEN22LA181 · WPR13LA035
ACS tasks: PA.I.F — Weather Information · PA.I.H — Human Factors · PA.II.B — Engine Starting / Systems Preflight · PA.IX.C — Emergency Approach and Landing · PA.IX.D — Go-Around / Rejected Landing
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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