What happened
On 4 January 2014, a Rans S-6ES Coyote II, registration ZU-DVM, departed from Khunskraal Farm in Cape Infanta, Western Cape, with the intention of returning to Swellendam Airfield. The flight was part of a private operation following a brief stop to drop off a passenger.
Witnesses observed the aircraft taking off normally, though it initially appeared to be crabbing to the right. Shortly after clearing the nearby vegetation, the aircraft experienced a sudden stall and a sharp left turn. This was followed by a left wing drop that transitioned into a vertical spiral dive. The aircraft struck the ground in a nose-down attitude, resulting in the death of the pilot and the total destruction of the aircraft.
The investigation
SACAA AIID investigators examined the wreckage and the mechanical components of the aircraft. An engine teardown confirmed that the Rotax 912UL engine was in running condition prior to impact and that all engine-related damage was a result of the crash itself.
Metallurgical analysis focused on the control system. Investigators discovered that the right rudder control cable had fractured at the position of the guide. The failure was attributed to extensive mechanical wear caused by abrasion between the cable and the Teflon guide. This wear had gradually compromised the outer strands of the cable until the inner core failed under normal tension. Similar, though less severe, wear was noted on the left rudder cable.
Findings
- The primary cause of the accident was the failure of the right rudder control cable due to long-term mechanical abrasion.
- This failure led to a loss of aircraft control, specifically a sudden stall and a subsequent vertical spiral dive.
- The control cable brackets were positioned such that they were concealed, preventing the pilot from performing a visual inspection of the cables during pre-flight checks.
- While weather conditions included broken clouds and moderate winds, they were not determined to be a contributing factor to the crash.