What happened
On 29 January 2019, a Pitts Special S-2B with registration ZS-OOB was returning to Rand Aerodrome in Johannesburg following an aerobatic training session near Kliprivier. While flying at approximately 500 feet above ground level, the pilot experienced a sudden loud bang and observed smoke emanating from the engine compartment. The pilot reported seeing oil spray across the windshield immediately before the engine ceased operation.
In an attempt to manage the emergency, the pilot searched for a suitable landing site and executed a forced landing. However, the aircraft struck uneven terrain with significant force, resulting in a nose-down and left-wing low position. The impact caused the total destruction of the aircraft. The pilot sustained serious injuries and was subsequently transported to a local hospital via ambulance.
The investigation
SACAA AIID investigators examined the aircraft's maintenance history and engine components to determine the cause of the power loss. The inspection of the engine revealed that the No. 3 and No. 6 cylinder connecting rods had failed. Specifically, the investigators found evidence of blackening, heat tinting, and melted slip bearings on the big-ends of the rods, indicating extreme thermal stress.
Review of the maintenance logs showed that the engine had exceeded its maximum tolerable time between overhaul (TBO). While the standard TBO was 1400 hours, the engine's use in aerobatic maneuvers required a reduced interval of 1330 hours; at the time of the accident, the engine had already surpassed this limit. Furthermore, investigators found no records of recent oil replenishment or the required oil filter and screen cleaning.
Findings
- The primary cause of the engine failure was the overheating of the connecting rods and bearings due to insufficient lubrication.
- There was no evidence that the mandatory 25-hour oil change and screen cleaning intervals, as required by manufacturer Mandatory Service Bulletin No. 480F, were being followed.
- The operator failed to monitor or record engine oil consumption, and no evidence of recent oil top-ups was found in the flight logs.
- The engine was operating beyond its calculated safe TBO for aerobatic flight profiles.
Safety action
- It is recommended that the SACAA ensures operators and maintenance organizations strictly adhere to manufacturer-mandated maintenance instructions.
- The investigation highlighted the need for better monitoring of engine oil consumption by operators.
- A recommendation was made to review existing regulations regarding the flexibility of engine overhaul intervals for private operators to ensure they remain safe in light of modern manufacturer service bulletins.