The student pilot was conducting a solo cross-country flight in the Cessna 150. The first leg was planned from Tullahoma Regional Airport/William Northern Field (KTHA), in Tullahoma, Tennessee, to Hassell Field Airport (M29), in Clifton, Tennessee, which was about 90 nm.
Shortly after receiving a weather briefing and flight instructor sign-off for the solo flight, the student pilot ensured the fuel was topped off. The preflight inspection and engine run-up were normal with no irregularities found. The subsequent takeoff and climb to the cruising altitude were normal.
About 80 nm into the flight, while cruising at 2,500 feet mean sea level and 2,400 rpm, the engine began to run rough. The pilot moved the throttle to full, confirmed that the mixture was full rich, and checked the fuel selector valve.
She did not report using carburetor heat at any point during her troubleshooting efforts.
The engine continued to progressively operate rougher with a subsequent decrease in rpm and the pilot was unable to maintain altitude.
She elected to divert to Paul Bridges Field (0M3), in Hohenwald, Tennessee.
While on final approach, the airplane was high and fast, however the pilot did not believe the airplane was high enough to bleed off airspeed and make a 180° turn to lose altitude, so she continued the approach and landed long down the runway.
Unable to stop the on the remaining runway using full brakes, the airplane exited the paved surface of the runway and struck a fence, resulting in substantial damage to the wings and elevator.
A visual inspection of the engine was conducted at the accident scene, and a visual inspection of fuel samples from the engine and wing drains found no sign of water or obstructions. A post-accident engine run was conducted and revealed no anomalies that would have prevented normal operation.
According to the FAA carburetor icing chart, the temperature, 2°C, and dew point, -2°C, recorded at the weather reporting station closest to the accident site, were conducive to “serious icing” at cruise power settings.
Probable Cause: The pilot’s failure to use carburetor heat in conditions conducive to the formation of carburetor ice, which resulted in a partial loss of engine power due to fuel starvation. Contributing to the outcome was her failure to attain a proper touchdown point during the subsequent diversionary landing, which resulted in a runway excursion.
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This January 2024 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Too many moving parts….
And…. The 150 will come down with full flaps!
And if still high, nose down and slip from side to side!
That bird will come down! No need to fly over usable runway!
I don’t think most students (at least in the flatlands) are taught how to lean or what the mixture knob is for (or they take it from the POH that the aircraft will crash and burn if they move the mixture off of the firewall below 3000 ft).
C150M poh – ROUGH ENGINE OPERATION OR LOSS OF POWER
CARBURETOR ICING
A gradual loss of RPM and eventual engine roughness may result from
the formation of carburetor ice. To clear the ice, apply full throttle and
pull the carburetor heat knob full out until the engine runs smoothly; then
remove carburetor heat and readjust the throttle. If conditions require the
continued use of carburetor heat in cruise flight, use the minimum amount
of heat necessary to prevent ice from forming and lean the mixture slightly
for smoothest engine operation.
Instructors fault for not teaching about carb ice. I find many pilots who don’t understand it. All the carburetor planes before 1960 had carb temp gages. Some how manufactured planes thought they saved money by not installing a gage. My opinion is that every carburetor engine should have a gage and the pilot needs to understand its use. On Fixed pitch prop the loss of RPM shows you have carb ice. Constant speed prop, Manifold pressure drop means carb ice present. If not sure pull carb heat on every 15 minutes for one minute. When carb heat is pulled on and the engine stumbles, you had ice. With a gage you can put partial heat on to stay out of the icing temperature zone. This is one of the most misunderstood systems on the plane and pilots are damaging planes way to often.