Engine Roughness Over Clearwater

Departing Clearwater Air Park (KCLW), Clearwater, FL — Runway 34, climbing out on a 335° heading. Elevation 71 ft MSL; the runway is essentially at sea level. You are on a local VFR flight, solo, full fuel, within limits.

It is a hazy Florida afternoon in late spring: OAT 29°C, dew point 23°C, altimeter 29.92. Scattered clouds at 2,500 ft, light rain shower two miles 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.' KCLW is non-towered (CTAF 122.8); you are in Class G airspace below 3,000 ft MSL. Above 3,000 ft MSL, you are in the overlying Tampa Class B airspace (3,000 MSL → 10,000 MSL).

You are 500 ft AGL, climbing through 75 KIAS (near Vy of 73 KIAS), heading 335°, when the engine begins to run rough. Power is noticeably down — the tachometer is dropping. The off-field environment ahead (Runway 34 climb-out) is low-density development, medium development, and open developed areas (parks, large lots) — not ideal for a forced landing, but better than dense urban. KCLW's own runway is behind you and to the left.

Aircraft: Cessna 172N, solo, full fuel, within limits. Carbureted Lycoming O-320, fixed-pitch prop, steam panel, 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. You are familiar with KCLW but have not trained extensively in forced-landing site selection. You know the field is surrounded by development, but you have not studied the off-field options in detail.

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 — even with carb heat applied, the ice accumulation was too heavy and too rapid.

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 roughness is carburetor ice — magneto failure, fuel contamination, and mechanical problems are also in the differential diagnosis.

NTSB WPR14LA099B (2014): A Piper PA-24 on a personal cross-country flight experienced partial engine power loss during initial climb due to water-contaminated fuel. The accident resulted from the pilot's failure to sump the fuel tanks during preflight, allowing water contamination to cause engine failure. Fuel sumping is a non-negotiable preflight step — water in the fuel tank is invisible until it reaches the engine.

The real accidents cited above occurred at other airports and in other aircraft — NOT at Clearwater Air Park (KCLW). KCLW has its own accident history (dominant pattern: forced landing 22.2%, loss of control 18.5%, gear-up landing 18.5%, hard landing 11.1%, fuel starvation 11.1%), but these specific events happened elsewhere. The scenario is localized to KCLW 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.