What happened
On 6 September 2009, a Piper Cherokee PA28-140, registration ZS-AKS, was conducting a private flight from Rand Aerodrome. While orbiting the Vanderbijlpark general flying area at approximately 7,000 feet, the pilot experienced a sudden loss of engine power and was unable to maintain altitude.
After declaring a Mayday to the Rand control tower, the pilot identified a suitable landing site. To avoid obstacles such as electric poles and fencing, the pilot executed a turn toward a recently ploughed field. The aircraft made a hard impact on its right main gear, followed by the left main gear and nose gear. Upon impact, the nose gear strut failed, causing the aircraft to nose over. The pilot and passenger, both of whom sustained minor injuries, were able to exit the aircraft immediately. The aircraft sustained substantial damage to the wings, engine cowling, propeller, and tail section.
The investigation
SACAA AIID investigators examined the engine and ignition components following the recovery of the aircraft to Wonderboom aerodrome. During testing, the engine was found to be running extremely roughly, operating on only a single cylinder.
Upon inspection, investigators discovered that the induction gasket for the fourth cylinder was missing. Furthermore, six spark plugs from the first, second, and fourth cylinders were found to be unserviceable. These plugs exhibited a thick brown/yellowish glazing on the insulator noses, a condition caused by high engine loading during extended use, which leads to conductivity and engine misfiring. Additionally, several plugs showed signs of external rust.
Findings
- The engine failure was caused by faulty spark plugs that had likely not been replaced during the last mandatory periodic inspection (MPI).
- The investigation noted that the last MPI was performed in January 2009 by a maintenance organization whose approval had since been revoked by the SACAA.
- The condition of the spark plugs suggests they had been in service for a considerable period without being replaced or properly inspected.
- The investigation concluded that the engine failure resulted from a lack of adequate maintenance and collective complacency by both the operator and the maintenance organization.