What happened
On 19 June 2025, a flight instructor and a student pilot were conducting training circuits at Lanseria International Airport in Gauteng. The flight, operating under Part 141 regulations, involved a Diamond DA-20-C1 with registration ZS-SJZ. The crew was performing a series of take-off and landing simulations, specifically practicing engine failure after take-off (EFATO) procedures.
During the fifth circuit, while at an altitude of approximately 500 feet, the crew initiated a second EFATO simulation. As the aircraft descended to 226 feet, the instructor attempted to recover engine power by opening the throttle, but the engine failed to respond. The instructor took control to attempt a recovery, but the power loss persisted. The instructor then identified a nearby field for an emergency landing.
The aircraft entered a field covered in thick, tall grass. During the landing roll, the aircraft struck a fence, bounced, and crossed over a dirt road before hitting a second fence. The impact caused the nose landing gear to fail. The aircraft slid for 24 metres, scraping the nose section against the ground before coming to a stop. While the aircraft sustained substantial damage to the nose gear and minor damage to the wing leading edges, both occupants disembarked without injury.
The investigation
SACAA AIID investigators conducted an engine-run test at the operator's maintenance facility to examine the Continental R-IO-240-B32B engine. The inspection revealed that the No. 4 exhaust valve was stuck in a partially open position, which created significant back pressure and caused the engine to backfire and vibrate abnormally.
Upon further examination, investigators found that the rocker arm attachment studs had sheared off, causing the rocker arm cover to become loose and the valve to lose proper actuation. This mechanical failure prevented the valve from opening and closing correctly, leading to a loss of compression in the cylinder and the subsequent loss of engine power.
Findings
- The primary cause of the engine power loss was the failure of the No. 4 cylinder exhaust valve rocker arm.
- The rocker arm became inoperative because the mounting studs had broken.
- Improper torque application on the rocker arm studs is the suspected contributing factor that compromised the components under operational load.
- The engine was relatively new, having completed only 194.5 hours since installation.