What happened
On December 28, 2016, a Cessna 152, registration PR-KNE, was performing a local instructional flight at the Guarapari Aerodrome (SNGA) in Espírito Santo, Brazil. The aircraft was occupied by a flight instructor and a student pilot. During the return leg of the flight, approximately 4 nautical miles from the airfield, the crew experienced intense engine vibration and abnormal noise, followed by a significant loss of engine power.
The instructor took control of the aircraft to perform an emergency landing. The aircraft touched down on the final third of the runway; however, due to the remaining runway length, the aircraft could not come to a complete stop within the paved limits, resulting in a runway excursion. The impact caused substantial damage to the nose gear, engine mount, lower engine cowling, right wing, and rudder. Both occupants were uninjured.
The investigation
CENIPA investigators examined the Lycoming 0-235-L2C engine and identified that the lower spark plug of cylinder number one had detached. Laboratory analysis conducted by the Department of Aerospace Science and Technology (DCTA) revealed that the failure was caused by wear in the cylinder's female thread, which led to the subsequent detachment of the helicoil along with the spark plug.
The investigation noted that the aircraft had undergone a 100-hour inspection just seven days prior to the accident. According to the Lycoming Operator’s Manual, such inspections require the removal, testing, and cleaning of spark plugs. The investigation determined that the failure to identify the thread wear during this recent maintenance period indicated that the inspection services were not performed adequately.
Findings
- Inadequate maintenance: The failure to detect the worn cylinder threads during the 100-hour inspection was a contributing factor.
- Management oversight: Deficiencies in the technical supervision of maintenance activities within the organization contributed to the occurrence.
- Pilot judgment: The decision-making regarding the emergency landing parameters contributed to the aircraft exceeding the runway limits.
Safety action
CENIPA issued a safety recommendation to the National Civil Aviation Agency (ANAC) to work with the operator to ensure that 50-hour and 100-hour inspections for Lycoming O-235 and O-290 series engines strictly adhere to the manufacturer's manual and regulatory requirements regarding the removal, analysis, and installation of spark plugs.