What happened
On September 7, 2019, a Cessna 152, registration PP-CHB, departed from Divinópolis, MG, bound for Conselheiro Lafaiete, MG, for a flight instruction mission. Approximately twenty minutes into the flight, the crew experienced engine oscillations. The pilots initiated emergency checklists and executed a forced landing alongside a highway near the Piracema junction in the municipality of Itaguara, MG. The aircraft sustained substantial damage, but both occupants emerged uninjured.
The investigation
CENIPA investigators examined the engine and the aircraft's maintenance records. While the engine's ignition system and magnetos were functioning correctly, investigators discovered that the installed carburetor (part number 10-5257) was not the approved model for the Lycoming O-235L2C engine powering the aircraft. This specific part number was intended for a different engine model with a lower continuous power rating. Additionally, the investigation found excessive play in the carburetor butterfly valve shaft, though no corrective maintenance for this issue was recorded.
Analysis of meteorological data from nearby stations indicated that at the flight altitude of approximately 6,000 ft, temperature and humidity levels were highly favorable for carburetor icing. Furthermore, the investigation noted that the carburetor heat control knob was found in the 'off' position at the time of the accident.
Findings
- The installed carburetor was not approved for the specific engine model installed in the aircraft.
- Maintenance records for the airframe and engine were not up to date.
- Atmospheric conditions were conducive to the formation of ice within the carburetor.
- The pilot did not utilize the carburetor heat system to prevent or mitigate icing.
- The engine experienced power loss due to suspected ice accumulation.