What happened
On 29 October 2024, a Piper PA-28-180 aircraft, registration ZS-WHV, departed Springs Airfield in Gauteng for a private flight to Bethlehem Airfield. During the cruise phase of the flight at 7,500 feet, the engine began running roughly, and the engine RPM dropped significantly from 2,500 to 1,500. Despite the pilot's attempts to adjust the power lever and lean the mixture, the engine could not maintain altitude.
After approximately ten minutes of struggling to rectify the power loss, the pilot determined that reaching the intended destination was impossible. After declaring an emergency via radio and squawking 7700, the pilot opted to perform a forced landing in a field located approximately 3.7 kilometers northwest of Reitz Airfield. The aircraft landed without sustaining any damage, and both the pilot and passenger disembarked from the 0 fatalities, 0 injuries incident unharmed.
The investigation
SACAA AIID investigators examined the engine and its components following the incident. While the fuel was found to be free of contaminants, a detailed inspection of the ignition system revealed that four of the eight spark plugs were heavily contaminated with carbon deposits and oil.
Further technical analysis of the Lycoming engine showed that the oil control rings had become worn, causing the clearance between the piston ring and the groove to exceed the maximum allowable limit of 0.006 inches. This wear allowed excessive oil to escape onto the cylinder walls and enter the combustion chamber.
Findings
- The primary cause of the engine power loss was fouled spark plugs contaminated with oil and carbon.
- The fouling was directly caused by worn-out oil control rings that failed to effectively regulate oil on the cylinder walls.
- The pilot was properly licensed and the aircraft's airworthiness documentation was up to date.
- Weather conditions were clear and were not a contributing factor to the incident.
- The engine had accumulated 480 hours since its last overhaul, during which time the rings had degraded beyond serviceable limits.