What happened
On September 11, 2020, an Aero Boero AB-115, registration PP-FLJ, departed from Bauru Airport (SBBU) for a local training flight. The crew consisted of a flight instructor and a student pilot. Shortly after takeoff, while performing a left-hand turn to clear arriving traffic, the aircraft experienced a sudden loss of engine power following an audible explosion from the engine.
As the aircraft lost airspeed and the stall warning activated, the instructor took control and attempted to manage the descent. The crew performed a forced landing on the median of the Marechal Rondon Highway. While the aircraft sustained substantial damage, both occupants escaped with minor injuries.
The investigation
CENIPA's investigation focused on the engine's mechanical condition and the aircraft's operational parameters. Investigators examined the Lycoming O-235-C2A engine and found that while fuel, lubrication, and ignition systems were functional, a critical defect was present in cylinder number 4.
Upon inspection, investigators discovered that the lower spark plug of the fourth cylinder had been expelled from its housing. The investigation revealed that an unapproved, artisanally manufactured bushing had been installed in the cylinder head to replace a standard helicoil. This bushing, which was not authorized by the manufacturer, had failed under the high operational stresses of takeoff, causing the spark plug to be ejected and resulting in the loss of power.
Furthermore, the investigation found that the aircraft was operating outside of its certified weight and balance limits. The aircraft had departed approximately 38 kg above its maximum takeoff weight, with the center of gravity exceeding the forward limit. This was due to the crew's failure to perform weight and balance calculations prior to the flight.
Findings
- The primary cause of the engine failure was the use of an unapproved part (an improvised bushing) in the spark plug housing of cylinder number 4.
- The aircraft was operating in an unsafe configuration, exceeding the maximum takeoff weight and deviating from the approved center of gravity limits.
- Inadequate maintenance supervision allowed an unauthorized component to remain undetected during recent 50-hour and 100-hour inspections.
- Deficiencies in the crew's decision-making process led to the omission of required weight and balance procedures.
Safety action
CENIPA issued recommendations to the National Civil Aviation Agency (ANAC) to improve supervision of flight instruction regarding weight and balance compliance. Additionally, recommendations were made to ensure maintenance organizations verify the conformity of services and strictly adhere to approved parts catalogs to prevent the use of unapproved components.