What happened
On the morning of 21 October 2023, a Beechcraft Sundowner C23, registration ZS-JKE, departed Bram Fischer International Airport (FABL) in the Free State for a planned flight to Wonderboom Airport. The aircraft was being operated under visual flight rules for a private mission with two pilots on board.
Shortly after takeoff, while the aircraft was climbing at approximately 350 feet above ground level, the engine experienced a significant power reduction. The pilot monitoring, who possessed more experience, took control of the aircraft and attempted an emergency forced landing in an open field located about one kilometer east of the runway 20 threshold. The aircraft struck the ground, spun 180 degrees, and immediately burst into flames. While a bystander was able to assist the pilot monitoring out of the wreckage, the pilot flying remained trapped and sustained fatal injuries. The pilot monitoring survived the impact but suffered serious injuries.
The investigation
Investigators from the SACAA AIID conducted a teardown inspection of the engine to determine the cause of the power loss. The examination revealed that the exhaust valve on the fourth cylinder was stuck in the open position, which led to a loss of compression in that cylinder.
Further review of the maintenance records showed that a Lycoming Service Bulletin (SB 388C), which mandates inspections to prevent valve issues caused by carbon buildup, had not been performed according to the required intervals. The engine had exceeded the recommended service interval by 252.3 hours at the time of the accident.
Findings
- The engine lost power during the initial climb due to a loss of compression in cylinder number four.
- The mechanical failure was caused by an exhaust valve stuck in the open position.
- The aircraft's maintenance history indicated that the required Service Bulletin 388C was overdue.
- The pilot's decision to depart the airport with a known engine defect served as a contributing factor to the accident.