Partial Power Loss on the Base-to-Final Turn

Departing Tampa International Airport (KTPA), Tampa, FL — Runway 19L, on a VFR local flight. Elevation 26 ft MSL. You are a Private pilot with 180 hours total, current and proficient. This is your second visit to KTPA; the first was a checkride. You know the field is towered 24/7, Class B airspace, and the off-field environment is dense development in all directions.

It is a warm, humid Florida afternoon in late spring: OAT 27°C, dew point 21°C, altimeter 29.91. Scattered clouds at 2,800 ft, light rain shower visible five miles to the southeast. Visibility 9 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.' You did not apply carburetor heat during the run-up because the engine ran smoothly. You did not apply it during climb because you were focused on the departure and the tower handoff.

You have completed a local flight and are now on base leg for Runway 19L, 800 ft AGL, 85 KIAS in a left turn. The runway is ahead and below. You are configured for landing: flaps 20°, gear fixed (as it always is), fuel selector BOTH, mixture rich. The tower has cleared you to land. You are about to turn final when the engine begins to run rough. Power is noticeably down — the tachometer is unwinding. You have roughly 20 seconds of useful decision time before you are committed to a landing — on the runway or off it.

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.

Pilot: you — a Private pilot, current, roughly 180 hours total. You are familiar with the C172M's marginal climb and acceleration, especially in heat and at gross weight. You know that the O-320 is carbureted and susceptible to carburetor ice in conducive conditions. You did not apply carburetor heat proactively during the descent because you were focused on the approach and did not perceive a risk.

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. 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, with insufficient time and altitude for carburetor heat to clear the accumulated ice.

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.

NTSB CEN22LA309 (2022): A Cessna 172M experienced engine power loss during cruise flight near Friend, Nebraska 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 shows that not all engine roughness is carburetor ice — mechanical failures (stuck valves, throttle cable failure, see WPR13LA035) can present the same way.

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 accident resulted from failure of the throttle control cable outer jacket, which fragmented and prevented proper throttle control. This case illustrates that throttle control issues can mimic power loss and require a different response.

The real accidents cited above occurred at other airports and in other aircraft — NOT at Tampa International Airport. KTPA has its own accident history (see field dominant patterns: FORCED_LANDING 22.2%, LOSS_OF_CONTROL_INFLIGHT 11.1%), but these specific events happened elsewhere. The scenario is localized to KTPA 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 C172M is insidious. It builds gradually during descent and approach, 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.

At KTPA, the off-field environment is dense development in all directions (off all runway ends). A forced landing off-field at KTPA is into a built-up area, not open terrain. This makes the decision to apply carburetor heat and continue to the runway — or to go around and troubleshoot — even more critical. The runway is always the better option if engine power can be restored.