What happened
On the morning of 27 June 2021, a Piper PA-28-180 Cherokee, registration ZS-ISU, was conducting a navigation training flight from Port Alfred Aerodrome in the Eastern Cape. The crew, consisting of a flight instructor and a student pilot, was flying under visual meteorological conditions along a route passing through Kenton on Sea and Bathurst.
While cruising at 4,500 feet, the instructor noticed the oil pressure had dropped to 60 psi and subsequently fell further to 20 psi. Simultaneously, the oil temperature rose sharply above 245°C. Shortly thereafter, a loud bang originated from the engine, followed by oil spraying across the windscreen. The student pilot issued a PAN-PAN call to Cape Town International Airport to declare an emergency. The instructor identified an open field near the R72 road, approximately 2 nautical miles northeast of Kenton on Sea, and successfully performed a forced landing. The aircraft sustained minor damage, and there were no injuries to the occupants.
The investigation
Following the incident, the engine was removed and subjected to a teardown examination under the supervision of a SACAA inspector. Investigators found significant metallic debris within the engine sump and oil filter. The examination revealed a hole measuring approximately 6 x 8 inches in the upper left portion of the crankcase, through which a substantial amount of oil had escaped.
While the oil pump and other main bearings appeared to be in good condition, the investigation focused on the No. 3 main bearing. Maintenance records showed that a 50-hour oil change and filter replacement had been performed just five days prior to the flight, and the engine had been operating within normal parameters during recent ground runs.
Findings
Technical analysis determined that the No. 3 main bearing oil gallery was blocked by unidentified foreign particles or contaminants. This blockage prevented the necessary supply of oil to the No. 3 connecting rod journal, leading to a loss of hydrodynamic lubrication. The resulting metal-to-metal contact caused the bearing to overheat significantly. This extreme heat caused the metal to expand, which likely compromised the integrity of the connecting rod bearing cap or the engine bolts, eventually leading to the detachment of the No. 3 connecting rod from the crankshaft journal.