Power Loss on Base — Peter O Knight
Partial engine failure in the traffic pattern over Tampa Bay; three runways, three different off-field realities, and a decision clock measured in seconds
The scenario
Departing Peter O Knight Airport (KTPF), Tampa, FL — Runway 22 (heading 217°), climbing out over Hillsborough Bay on a VFR local flight. Elevation 8 ft MSL. KTPF is non-towered Class G airspace; overlying Tampa Class B begins at 1,200 ft MSL.
It is a warm, humid Tampa afternoon in late spring: OAT 27°C, dew point 21°C, altimeter 29.94. Scattered clouds at 2,800 ft, light rain shower two miles to the northwest. Visibility 9 SM. Classic Gulf Coast conditions — the FAA icing probability chart marks this as 'serious icing at glide power, moderate icing at cruise power.' You are planning a local flight: climb to 1,500 ft MSL, cruise the bay, and return to KTPF for landing.
You climb out on Runway 22 to 1,200 ft MSL, turn crosswind, and level off. The engine is running smoothly. You are in the left downwind for Runway 22 at 1,200 ft MSL, 2.5 nm from the airport, when the engine begins to run rough. Power is noticeably down — the tachometer is unwinding. You are still over open water (Hillsborough Bay). The airport is behind you and to your right.
Aircraft: Cessna 172M, solo, full fuel, within limits. Carbureted Lycoming O-320-E2D, 150 hp, fixed-pitch prop, steam panel, fuel selector on BOTH. Nothing was written up; the airplane was airworthy at departure. The 172M is the lower-powered variant — climb and acceleration are marginal, especially in heat and at gross weight.
Pilot: you — a Private pilot, current, roughly 250 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 heads-down on the climb and crosswind turn. You are now at 1,200 ft MSL over water with a rough engine and a decision to make.
- {'label': 'Field', 'value': 'KTPF · Peter O Knight'}
- {'label': 'Runways', 'value': '4/22 · 18/36'}
- {'label': 'Elevation', 'value': '8 ft'}
- {'label': 'Aircraft', 'value': 'C172M'}
- {'label': 'Dominant phase', 'value': 'Landing / Approach'}
The decision
Before we get into the decision tree — what do you already know about engine failure in the traffic pattern? (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. The ambient conditions were 75°F OAT and 55°F dew point — 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. The student had not applied carburetor heat during the descent or approach.
NTSB CEN24LA168 (2024): A Cessna 172M on an IFR flight to Bemidji Regional Airport 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. The go-around with partial power failed; the airplane impacted terrain.
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 between corn crops, resulting in substantial fuselage damage. This case illustrates that not all engine-roughness events are carburetor ice — mechanical failures (stuck valves, throttle cable failure, etc.) also cause power loss.
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. This case shows that throttle-control mechanical failures can mimic engine failure.
The local environment at KTPF makes this scenario particularly unforgiving: Runway 22's climb-out end (heading 217°) is open water — Hillsborough Bay. Runway 36's climb-out end (heading 353°) is also open water. Runway 04's climb-out end (heading 37°) is dense development. An engine failure on the Runway 22 or 36 departure at low altitude is a ditching, not a field landing. This is the NLCD ground cover off those runway ends.
The consistent thread across all these events: carburetor ice in the C172M is insidious. It builds gradually, the first symptom is roughness and a dropping tachometer, 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 172M's lower power (150 hp vs. the 172N's 180 hp) makes climb performance marginal even with full power — a go-around with partial power is a high-risk maneuver.
Real accidents cited above occurred at other airports and in other aircraft — NOT at Peter O Knight Airport. KTPF has its own accident history (forced landing 19.4%, loss of control 16.7%, ditching 11.1%), but these specific NTSB events happened elsewhere. The scenario is localized to KTPF to make the off-field environment real and consequential for you as a student here.
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 — do not wait for the symptom to worsen. At KTPF, the off-field environment off Runway 22 and Runway 36 is open water: a delayed response means a ditching, not a field landing. The 172M's marginal climb performance (150 hp at gross weight) makes a go-around with partial power a high-risk maneuver — if you must go around, apply carb heat immediately and be prepared to return to the runway if climb is insufficient.
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 (like on approach or descent) 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 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 and on descent / approach.
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 KTPF, an engine failure on the Runway 22 or Runway 36 departure is a ditching.
The off-field environment off Runway 22's climb-out end (heading 217°) and Runway 36's climb-out end (heading 353°) is open water — Hillsborough Bay. There is no alternate landing surface. If the engine quits on the Runway 22 or 36 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 65 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 22 or 36.
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 27°C and dew point near 21°C, that means applying carb heat during the descent from cruise, before entering the pattern. Waiting for the roughness to appear at 800 ft AGL on base leg is waiting too long. The decision window is measured in seconds, not minutes.
The 172M's climb performance is marginal — a go-around with partial power is high-risk.
The C172M is the lower-powered variant of the 172 family: 150 hp vs. the 172N's 180 hp. Climb performance is marginal even with full power at gross weight, especially in heat and high density altitude. A go-around from a low approach (600 ft AGL) with partial power is a high-risk maneuver — the airplane may not have the climb performance to clear obstacles or gain altitude. If you must go around, apply carb heat immediately to restore power if possible. If climb is insufficient, return to the runway and land. Do not try to stretch a go-around with a sick engine.
Built from the real accident record
Scenario built from NTSB ERA09LA379 (2009 C172M carburetor ice on base-to-final), 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 KTPF.
NTSB reports: ERA09LA379 · CEN24LA168 · CEN22LA309 · CEN22LA181 · WPR13LA035
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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