What happened
On 29 November 2019, a Cessna 206C, registration ZS-EZK, was conducting an aerial survey mission over the Port Alfred area. The flight, operated under Part 137 regulations, was returning to Port Elizabeth Aerodrome (FAPE) when the pilot and photographer experienced a sudden, loud bang from the engine compartment. This was immediately followed by intense engine vibration, abnormal noise, and a visible cloud of white smoke.
Upon reviewing engine instruments, the pilot identified low oil pressure. Despite the developing situation, the pilot maintained control of the aircraft and declared a MAYDAY to air traffic control. While the engine initially continued to run, a second loud bang occurred minutes later, accompanied by an oil leak that coated the engine cowlings and windscreen. This second event led to a loss of engine power due to a drop in manifold pressure. The pilot successfully utilized the remaining engine power to perform a safe emergency landing on Runway 26 at Port Elizabeth Aerodrome. There were no injuries to the two occupants, though the engine sustained significant damage.
The investigation
An investigation by the SACAA AIID focused on the Continental TSIO-520-C engine. A teardown examination at an independent facility revealed that the No. 4 connecting rod and piston had disconnected from the crankshaft journal, with the connecting rod shaft showing a fracture. The force of the failure was severe enough to punch a hole through the top left side of the crankcase.
Investigators examined the engine's lubrication system and maintenance history. While the oil pump was operational and the oil system showed no signs of internal or external leaks, evidence of heat discoloration was found on the No. 4 camshaft journal area. Maintenance records indicated that a 50-hour oil change had been performed on 13 November 2019. However, calculations based on the engine's known consumption rate suggested that the oil level had depleted significantly since that service.
Findings
- The primary cause of the incident was the separation of the No. 4 connecting rod big end bearing cap.
- This failure was driven by excessive heat concentrated on the No. 4 camshaft journal area.
- The heat was a direct result of oil starvation at that specific journal.
- The engine was likely operating with an oil quantity below the manufacturer's minimum requirement of 6 quarts.
- A contributing factor was an inadequate pre-flight inspection, specifically the failure to verify the oil level using the dipstick prior to departure.