What happened
On 18 July 2009, a private Beech 36 (registration ZS-MPB) was conducting a VFR flight from Stellenbosch to Upington. During the cruise phase, the pilot noticed smoke and the smell of oil inside the cockpit. This was followed by a drop in oil pressure and an unrecorded uncontained engine failure.
Fearing an in-flight fire, the pilot deactivated the master switch and prepared for an emergency landing. The pilot attempted to extend the landing gear; however, because the electrical master switch had been turned off, the gear failed to deploy. The aircraft subsequently performed a forced landing on a gravel road approximately 25 km west of Kenhardt. While the pilot escaped without injury, the aircraft sustained significant damage to the engine, propeller, and undercarriage.
The investigation
SACAA AIID investigators examined the aircraft's recent maintenance history and found that the engine had recently undergone repairs to replace a worn starter clutch. The investigation revealed that the replacement starter clutch assembly was supplied from another aircraft and lacked an optional air-conditioning drive. Because this specific configuration was used, a clip seal retainer was required to secure the oil seal.
Technicians had noted the difference in the part's appearance but proceeded with the installation. During the process, the clip seal retainer was omitted, which allowed the oil seal to become dislodged during flight. This led to the rapid loss of engine oil and the subsequent engine seizure.
Findings
- The primary cause of the engine failure was the omission of a clip seal retainer during the installation of the starter clutch.
- The loss of lubrication caused the engine to suffer an uncontained failure.
- The landing gear remained retracted because the electrical master switch had been disarmed prior to the gear extension attempt.
- The pilot did not utilize the manual emergency gear extension method.
- The pilot's response to the engine failure suggested an inadequate understanding of the aircraft's emergency procedures and systems.